#![allow(non_snake_case)]

//! Frozen decoder for the zstd v0.1 format.
//!
//! This is a line-by-line port of `lib/legacy/zstd_v01.c`: the same table
//! layouts, the same arithmetic, and the same error codes.  The C file is a
//! self-contained snapshot of the v0.1-era FSE and Huff0 coders, so this
//! module deliberately reimplements them instead of reusing the modern
//! `fse_decompress`/`huf_decompress` modules (see `legacy/mod.rs` for the
//! frozen-decoder policy).  The only shared dependency is `crate::errors`,
//! mirroring the C file's `error_private.h` include.
//!
//! The streaming `ZSTDv01_Dctx` state lives entirely in Rust; C callers only
//! ever hold an opaque pointer to it.  It is allocated with `libc::malloc`
//! and released with `libc::free`, exactly like the original C context.

use crate::errors::{ERR_isError, ZstdErrorCode, ERROR};
use std::os::raw::{c_uint, c_void};
use std::ptr;

/* ******************************************
 *  Error management (frozen v0.1 FSE codes)
 ********************************************/
/* FSE_LIST_ERRORS in zstd_v01.c; values are returned as `(size_t)-code`. */
const FSE_ERROR_GENERIC: usize = 1;
const FSE_ERROR_TABLELOG_TOO_LARGE: usize = 2;
const FSE_ERROR_MAX_SYMBOL_VALUE_TOO_LARGE: usize = 3;
const FSE_ERROR_MAX_SYMBOL_VALUE_TOO_SMALL: usize = 4;
const FSE_ERROR_DST_SIZE_TOO_SMALL: usize = 5;
const FSE_ERROR_SRC_SIZE_WRONG: usize = 6;
const FSE_ERROR_CORRUPTION_DETECTED: usize = 7;
const FSE_ERROR_MAX_CODE: usize = 8;

#[inline]
fn fse_error(code: usize) -> usize {
    code.wrapping_neg()
}

#[inline]
fn fse_is_error(code: usize) -> bool {
    code > fse_error(FSE_ERROR_MAX_CODE)
}

/* ******************************************
 *  Tuning parameters (frozen)
 ********************************************/
const FSE_MAX_MEMORY_USAGE: u32 = 14;
const FSE_MAX_SYMBOL_VALUE: u32 = 255;

const FSE_MAX_TABLELOG: u32 = FSE_MAX_MEMORY_USAGE - 2;
const FSE_MIN_TABLELOG: u32 = 5;
const FSE_TABLELOG_ABSOLUTE_MAX: u32 = 15;

const HUF_MAX_SYMBOL_VALUE: u32 = 255;
const HUF_MAX_TABLELOG: u32 = 12;
const HUF_ABSOLUTEMAX_TABLELOG: u32 = 16;

const IS_32BITS: bool = std::mem::size_of::<usize>() == 4;
const USIZE_BITS: u32 = usize::BITS;

/* ******************************************
 *  Memory I/O (FSE_read* / ZSTD_read* helpers)
 ********************************************/
#[inline]
unsafe fn fse_read_le16(mem_ptr: *const u8) -> u16 {
    u16::from_le_bytes(ptr::read_unaligned(mem_ptr as *const [u8; 2]))
}

#[inline]
unsafe fn fse_read_le32(mem_ptr: *const u8) -> u32 {
    u32::from_le_bytes(ptr::read_unaligned(mem_ptr as *const [u8; 4]))
}

#[inline]
unsafe fn fse_read_le64(mem_ptr: *const u8) -> u64 {
    u64::from_le_bytes(ptr::read_unaligned(mem_ptr as *const [u8; 8]))
}

#[inline]
unsafe fn fse_read_lest(mem_ptr: *const u8) -> usize {
    if IS_32BITS {
        fse_read_le32(mem_ptr) as usize
    } else {
        fse_read_le64(mem_ptr) as usize
    }
}

/// `FSE_highbit32`; the caller guarantees `val != 0`, as in C.
#[inline]
fn fse_highbit32(val: u32) -> u32 {
    val.leading_zeros() ^ 31
}

/* ******************************************
 *  FSE structures
 ********************************************/
#[repr(C)]
#[derive(Clone, Copy)]
struct FseDecode {
    new_state: u16,
    symbol: u8,
    nb_bits: u8,
}

#[repr(C)]
struct FseDTableHeader {
    table_log: u16,
    fast_mode: u16,
}

struct FseDStream {
    bit_container: usize,
    bits_consumed: u32,
    ptr: *const u8,
    start: *const u8,
}

struct FseDState {
    state: usize,
    table: *const FseDecode,
}

const FSE_DSTREAM_UNFINISHED: u32 = 0;
const FSE_DSTREAM_END_OF_BUFFER: u32 = 1;
const FSE_DSTREAM_COMPLETED: u32 = 2;
const FSE_DSTREAM_TOO_FAR: u32 = 3;

#[inline]
fn fse_table_step(table_size: u32) -> u32 {
    (table_size >> 1) + (table_size >> 3) + 3
}

/* An FSE_DTable is an opaque u32 array: one header word followed by
 * `1 << tableLog` FseDecode entries, exactly as in C. */
unsafe fn fse_build_dtable(
    dt: *mut u32,
    normalized_counter: *const i16,
    max_symbol_value: u32,
    table_log: u32,
) -> usize {
    let dtable_h = dt as *mut FseDTableHeader;
    let table_decode = dt.add(1) as *mut FseDecode;

    /* Sanity checks */
    if max_symbol_value > FSE_MAX_SYMBOL_VALUE {
        return fse_error(FSE_ERROR_MAX_SYMBOL_VALUE_TOO_LARGE);
    }
    if table_log > FSE_MAX_TABLELOG {
        return fse_error(FSE_ERROR_TABLELOG_TOO_LARGE);
    }

    let table_size: u32 = 1 << table_log;
    let table_mask = table_size - 1;
    let step = fse_table_step(table_size);
    let mut symbol_next = [0u16; (FSE_MAX_SYMBOL_VALUE + 1) as usize];
    let mut position: u32 = 0;
    let mut high_threshold = table_size - 1;
    let large_limit = (1i32 << (table_log - 1)) as i16;
    let mut no_large: u32 = 1;

    /* Init, lay down lowprob symbols */
    (*dtable_h).table_log = table_log as u16;
    for s in 0..=max_symbol_value {
        let count = *normalized_counter.add(s as usize);
        if count == -1 {
            (*table_decode.add(high_threshold as usize)).symbol = s as u8;
            high_threshold = high_threshold.wrapping_sub(1);
            symbol_next[s as usize] = 1;
        } else {
            if count >= large_limit {
                no_large = 0;
            }
            symbol_next[s as usize] = count as u16;
        }
    }

    /* Spread symbols */
    for s in 0..=max_symbol_value {
        let count = *normalized_counter.add(s as usize);
        let mut i = 0i32;
        while i < count as i32 {
            (*table_decode.add(position as usize)).symbol = s as u8;
            position = (position + step) & table_mask;
            while position > high_threshold {
                position = (position + step) & table_mask; /* lowprob area */
            }
            i += 1;
        }
    }

    if position != 0 {
        /* position must reach all cells once, otherwise normalizedCounter is incorrect */
        return fse_error(FSE_ERROR_GENERIC);
    }

    /* Build Decoding table */
    for i in 0..table_size as usize {
        let symbol = (*table_decode.add(i)).symbol;
        let next_state = symbol_next[symbol as usize];
        symbol_next[symbol as usize] = next_state.wrapping_add(1);
        let nb_bits = (table_log - fse_highbit32(next_state as u32)) as u8;
        (*table_decode.add(i)).nb_bits = nb_bits;
        (*table_decode.add(i)).new_state =
            (((next_state as u32) << nb_bits).wrapping_sub(table_size)) as u16;
    }

    (*dtable_h).fast_mode = no_large as u16;
    0
}

/* ******************************************
 *  FSE header bitstream (FSE_readNCount)
 ********************************************/
unsafe fn fse_read_ncount(
    normalized_counter: *mut i16,
    max_sv_ptr: &mut u32,
    table_log_ptr: &mut u32,
    header_buffer: *const u8,
    hb_size: usize,
) -> usize {
    let istart = header_buffer;
    let iend_addr = (istart as usize).wrapping_add(hb_size);
    let mut ip = istart;
    let mut charnum: u32 = 0;
    let mut previous0 = false;

    if hb_size < 4 {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }
    let mut bit_stream = fse_read_le32(ip);
    let mut nb_bits: i32 = ((bit_stream & 0xF) + FSE_MIN_TABLELOG) as i32; /* extract tableLog */
    if nb_bits > FSE_TABLELOG_ABSOLUTE_MAX as i32 {
        return fse_error(FSE_ERROR_TABLELOG_TOO_LARGE);
    }
    bit_stream >>= 4;
    let mut bit_count: i32 = 4;
    *table_log_ptr = nb_bits as u32;
    let mut remaining: i32 = (1 << nb_bits) + 1;
    let mut threshold: i32 = 1 << nb_bits;
    nb_bits += 1;

    while remaining > 1 && charnum <= *max_sv_ptr {
        if previous0 {
            let mut n0 = charnum;
            while (bit_stream & 0xFFFF) == 0xFFFF {
                n0 += 24;
                if (ip as usize) < iend_addr.wrapping_sub(5) {
                    ip = ip.add(2);
                    bit_stream = fse_read_le32(ip).wrapping_shr(bit_count as u32);
                } else {
                    bit_stream >>= 16;
                    bit_count += 16;
                }
            }
            while (bit_stream & 3) == 3 {
                n0 += 3;
                bit_stream >>= 2;
                bit_count += 2;
            }
            n0 += bit_stream & 3;
            bit_count += 2;
            if n0 > *max_sv_ptr {
                return fse_error(FSE_ERROR_MAX_SYMBOL_VALUE_TOO_SMALL);
            }
            while charnum < n0 {
                *normalized_counter.add(charnum as usize) = 0;
                charnum += 1;
            }
            if (ip as usize) <= iend_addr.wrapping_sub(7)
                || (ip as usize).wrapping_add((bit_count >> 3) as usize)
                    <= iend_addr.wrapping_sub(4)
            {
                ip = ip.add((bit_count >> 3) as usize);
                bit_count &= 7;
                bit_stream = fse_read_le32(ip).wrapping_shr(bit_count as u32);
            } else {
                bit_stream >>= 2;
            }
        }
        {
            let max: i16 = ((2 * threshold - 1) - remaining) as i16;
            let mut count: i16;

            if (bit_stream & (threshold - 1) as u32) < max as i32 as u32 {
                count = (bit_stream & (threshold - 1) as u32) as u16 as i16;
                bit_count += nb_bits - 1;
            } else {
                count = (bit_stream & (2 * threshold - 1) as u32) as u16 as i16;
                if count as i32 >= threshold {
                    count = ((count as i32) - (max as i32)) as i16;
                }
                bit_count += nb_bits;
            }

            count = count.wrapping_sub(1); /* extra accuracy */
            remaining -= (count as i32).abs();
            *normalized_counter.add(charnum as usize) = count;
            charnum += 1;
            previous0 = count == 0;
            while remaining < threshold {
                nb_bits -= 1;
                threshold >>= 1;
            }

            if (ip as usize) <= iend_addr.wrapping_sub(7)
                || (ip as usize).wrapping_add((bit_count >> 3) as usize)
                    <= iend_addr.wrapping_sub(4)
            {
                ip = ip.add((bit_count >> 3) as usize);
                bit_count &= 7;
            } else {
                bit_count -=
                    (8 * (iend_addr.wrapping_sub(4) as isize - ip as usize as isize)) as i32;
                ip = (iend_addr - 4) as *const u8;
            }
            bit_stream = fse_read_le32(ip).wrapping_shr((bit_count & 31) as u32);
        }
    }
    if remaining != 1 {
        return fse_error(FSE_ERROR_GENERIC);
    }
    *max_sv_ptr = charnum - 1;

    ip = ip.wrapping_offset(((bit_count + 7) >> 3) as isize);
    if (ip as usize).wrapping_sub(istart as usize) > hb_size {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }
    (ip as usize).wrapping_sub(istart as usize)
}

/* ******************************************
 *  FSE decompression, byte symbols
 ********************************************/
unsafe fn fse_build_dtable_rle(dt: *mut u32, symbol_value: u8) -> usize {
    let dtable_h = dt as *mut FseDTableHeader;
    let cell = dt.add(1) as *mut FseDecode;

    (*dtable_h).table_log = 0;
    (*dtable_h).fast_mode = 0;

    (*cell).new_state = 0;
    (*cell).symbol = symbol_value;
    (*cell).nb_bits = 0;

    0
}

unsafe fn fse_build_dtable_raw(dt: *mut u32, nb_bits: u32) -> usize {
    let dtable_h = dt as *mut FseDTableHeader;
    let dinfo = dt.add(1) as *mut FseDecode;

    /* Sanity checks */
    if nb_bits < 1 {
        return fse_error(FSE_ERROR_GENERIC); /* min size */
    }
    let table_size: u32 = 1 << nb_bits;
    let table_mask = table_size - 1;
    let max_symbol_value = table_mask;

    (*dtable_h).table_log = nb_bits as u16;
    (*dtable_h).fast_mode = 1;
    for s in 0..=max_symbol_value {
        let cell = dinfo.add(s as usize);
        (*cell).new_state = 0;
        (*cell).symbol = s as u8;
        (*cell).nb_bits = nb_bits as u8;
    }

    0
}

unsafe fn fse_init_dstream(
    bit_d: &mut FseDStream,
    src_buffer: *const u8,
    src_size: usize,
) -> usize {
    let word = std::mem::size_of::<usize>();
    if src_size < 1 {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }

    if src_size >= word {
        bit_d.start = src_buffer;
        bit_d.ptr = src_buffer.add(src_size - word);
        bit_d.bit_container = fse_read_lest(bit_d.ptr);
        let contain32 = *src_buffer.add(src_size - 1) as u32;
        if contain32 == 0 {
            return fse_error(FSE_ERROR_GENERIC); /* stop bit not present */
        }
        bit_d.bits_consumed = 8 - fse_highbit32(contain32);
    } else {
        bit_d.start = src_buffer;
        bit_d.ptr = bit_d.start;
        bit_d.bit_container = *bit_d.start as usize;
        /* C switch with fallthrough over srcSize 7..2 */
        if src_size >= 7 {
            bit_d.bit_container += (*src_buffer.add(6) as usize) << (USIZE_BITS as usize - 16);
        }
        if src_size >= 6 {
            bit_d.bit_container += (*src_buffer.add(5) as usize) << (USIZE_BITS as usize - 24);
        }
        if src_size >= 5 {
            bit_d.bit_container += (*src_buffer.add(4) as usize) << (USIZE_BITS as usize - 32);
        }
        if src_size >= 4 {
            bit_d.bit_container += (*src_buffer.add(3) as usize) << 24;
        }
        if src_size >= 3 {
            bit_d.bit_container += (*src_buffer.add(2) as usize) << 16;
        }
        if src_size >= 2 {
            bit_d.bit_container += (*src_buffer.add(1) as usize) << 8;
        }
        let contain32 = *src_buffer.add(src_size - 1) as u32;
        if contain32 == 0 {
            return fse_error(FSE_ERROR_GENERIC); /* stop bit not present */
        }
        bit_d.bits_consumed = 8 - fse_highbit32(contain32);
        bit_d.bits_consumed += ((word - src_size) * 8) as u32;
    }

    src_size
}

#[inline]
unsafe fn fse_look_bits(bit_d: &FseDStream, nb_bits: u32) -> usize {
    let bit_mask = USIZE_BITS - 1;
    ((bit_d.bit_container << (bit_d.bits_consumed & bit_mask)) >> 1)
        >> (bit_mask.wrapping_sub(nb_bits) & bit_mask)
}

#[inline]
unsafe fn fse_look_bits_fast(bit_d: &FseDStream, nb_bits: u32) -> usize {
    /* only if nb_bits >= 1 */
    let bit_mask = USIZE_BITS - 1;
    (bit_d.bit_container << (bit_d.bits_consumed & bit_mask))
        >> ((bit_mask + 1).wrapping_sub(nb_bits) & bit_mask)
}

#[inline]
fn fse_skip_bits(bit_d: &mut FseDStream, nb_bits: u32) {
    bit_d.bits_consumed = bit_d.bits_consumed.wrapping_add(nb_bits);
}

#[inline]
unsafe fn fse_read_bits(bit_d: &mut FseDStream, nb_bits: u32) -> usize {
    let value = fse_look_bits(bit_d, nb_bits);
    fse_skip_bits(bit_d, nb_bits);
    value
}

#[inline]
unsafe fn fse_read_bits_fast(bit_d: &mut FseDStream, nb_bits: u32) -> usize {
    /* only if nb_bits >= 1 */
    let value = fse_look_bits_fast(bit_d, nb_bits);
    fse_skip_bits(bit_d, nb_bits);
    value
}

unsafe fn fse_reload_dstream(bit_d: &mut FseDStream) -> u32 {
    let word = std::mem::size_of::<usize>();
    if bit_d.bits_consumed > (word * 8) as u32 {
        /* should never happen */
        return FSE_DSTREAM_TOO_FAR;
    }

    if (bit_d.ptr as usize) >= (bit_d.start as usize).wrapping_add(word) {
        bit_d.ptr = bit_d.ptr.sub((bit_d.bits_consumed >> 3) as usize);
        bit_d.bits_consumed &= 7;
        bit_d.bit_container = fse_read_lest(bit_d.ptr);
        return FSE_DSTREAM_UNFINISHED;
    }
    if bit_d.ptr == bit_d.start {
        if bit_d.bits_consumed < (word * 8) as u32 {
            return FSE_DSTREAM_END_OF_BUFFER;
        }
        return FSE_DSTREAM_COMPLETED;
    }
    {
        let mut nb_bytes = bit_d.bits_consumed >> 3;
        let mut result = FSE_DSTREAM_UNFINISHED;
        if (bit_d.ptr as usize).wrapping_sub(nb_bytes as usize) < (bit_d.start as usize) {
            nb_bytes = ((bit_d.ptr as usize) - (bit_d.start as usize)) as u32; /* ptr > start */
            result = FSE_DSTREAM_END_OF_BUFFER;
        }
        bit_d.ptr = bit_d.ptr.sub(nb_bytes as usize);
        bit_d.bits_consumed -= nb_bytes * 8;
        bit_d.bit_container = fse_read_lest(bit_d.ptr); /* reminder : srcSize > sizeof(bitD) */
        result
    }
}

unsafe fn fse_init_dstate(d_state: &mut FseDState, bit_d: &mut FseDStream, dt: *const u32) {
    let dtable_h = dt as *const FseDTableHeader;
    d_state.state = fse_read_bits(bit_d, (*dtable_h).table_log as u32);
    fse_reload_dstream(bit_d);
    d_state.table = dt.add(1) as *const FseDecode;
}

unsafe fn fse_decode_symbol(d_state: &mut FseDState, bit_d: &mut FseDStream) -> u8 {
    let d_info = *d_state.table.add(d_state.state);
    let low_bits = fse_read_bits(bit_d, d_info.nb_bits as u32);
    d_state.state = (d_info.new_state as usize).wrapping_add(low_bits);
    d_info.symbol
}

unsafe fn fse_decode_symbol_fast(d_state: &mut FseDState, bit_d: &mut FseDStream) -> u8 {
    let d_info = *d_state.table.add(d_state.state);
    let low_bits = fse_read_bits_fast(bit_d, d_info.nb_bits as u32);
    d_state.state = (d_info.new_state as usize).wrapping_add(low_bits);
    d_info.symbol
}

#[inline]
fn fse_end_of_dstream(bit_d: &FseDStream) -> bool {
    bit_d.ptr == bit_d.start && bit_d.bits_consumed == USIZE_BITS
}

#[inline]
fn fse_end_of_dstate(d_state: &FseDState) -> bool {
    d_state.state == 0
}

unsafe fn fse_decompress_using_dtable_generic(
    dst: *mut u8,
    max_dst_size: usize,
    c_src: *const u8,
    c_src_size: usize,
    dt: *const u32,
    fast: bool,
) -> usize {
    let ostart = dst;
    let mut op = ostart;
    let omax_addr = (op as usize).wrapping_add(max_dst_size);
    let olimit_addr = omax_addr.wrapping_sub(3);

    let mut bit_d = FseDStream {
        bit_container: 0,
        bits_consumed: 0,
        ptr: ptr::null(),
        start: ptr::null(),
    };
    let mut state1 = FseDState {
        state: 0,
        table: ptr::null(),
    };
    let mut state2 = FseDState {
        state: 0,
        table: ptr::null(),
    };

    /* Init */
    let error_code = fse_init_dstream(&mut bit_d, c_src, c_src_size);
    if fse_is_error(error_code) {
        return error_code;
    }

    fse_init_dstate(&mut state1, &mut bit_d, dt);
    fse_init_dstate(&mut state2, &mut bit_d, dt);

    macro_rules! fse_getsymbol {
        ($state:expr) => {
            if fast {
                fse_decode_symbol_fast($state, &mut bit_d)
            } else {
                fse_decode_symbol($state, &mut bit_d)
            }
        };
    }

    /* Constant conditions from the C source; on 64-bit both are false, on
     * 32-bit only the *4 variant reloads. */
    const RELOAD_2: bool = FSE_MAX_TABLELOG * 2 + 7 > USIZE_BITS;
    const RELOAD_4: bool = FSE_MAX_TABLELOG * 4 + 7 > USIZE_BITS;

    /* 4 symbols per loop */
    while fse_reload_dstream(&mut bit_d) == FSE_DSTREAM_UNFINISHED && (op as usize) < olimit_addr {
        *op = fse_getsymbol!(&mut state1);

        if RELOAD_2 {
            /* This test must be static */
            fse_reload_dstream(&mut bit_d);
        }

        *op.add(1) = fse_getsymbol!(&mut state2);

        if RELOAD_4 {
            /* This test must be static */
            if fse_reload_dstream(&mut bit_d) > FSE_DSTREAM_UNFINISHED {
                op = op.add(2);
                break;
            }
        }

        *op.add(2) = fse_getsymbol!(&mut state1);

        if RELOAD_2 {
            /* This test must be static */
            fse_reload_dstream(&mut bit_d);
        }

        *op.add(3) = fse_getsymbol!(&mut state2);
        op = op.add(4);
    }

    /* tail */
    loop {
        if fse_reload_dstream(&mut bit_d) > FSE_DSTREAM_COMPLETED
            || (op as usize) == omax_addr
            || (fse_end_of_dstream(&bit_d) && (fast || fse_end_of_dstate(&state1)))
        {
            break;
        }

        *op = fse_getsymbol!(&mut state1);
        op = op.add(1);

        if fse_reload_dstream(&mut bit_d) > FSE_DSTREAM_COMPLETED
            || (op as usize) == omax_addr
            || (fse_end_of_dstream(&bit_d) && (fast || fse_end_of_dstate(&state2)))
        {
            break;
        }

        *op = fse_getsymbol!(&mut state2);
        op = op.add(1);
    }

    /* end ? */
    if fse_end_of_dstream(&bit_d) && fse_end_of_dstate(&state1) && fse_end_of_dstate(&state2) {
        return (op as usize) - (ostart as usize);
    }

    if (op as usize) == omax_addr {
        /* dst buffer is full, but cSrc unfinished */
        return fse_error(FSE_ERROR_DST_SIZE_TOO_SMALL);
    }

    fse_error(FSE_ERROR_CORRUPTION_DETECTED)
}

unsafe fn fse_decompress_using_dtable(
    dst: *mut u8,
    original_size: usize,
    c_src: *const u8,
    c_src_size: usize,
    dt: *const u32,
) -> usize {
    let fast_mode = (*(dt as *const FseDTableHeader)).fast_mode;

    /* select fast mode (static) */
    if fast_mode != 0 {
        return fse_decompress_using_dtable_generic(
            dst,
            original_size,
            c_src,
            c_src_size,
            dt,
            true,
        );
    }
    fse_decompress_using_dtable_generic(dst, original_size, c_src, c_src_size, dt, false)
}

unsafe fn fse_decompress(
    dst: *mut u8,
    max_dst_size: usize,
    c_src: *const u8,
    c_src_size: usize,
) -> usize {
    let istart = c_src;
    let mut ip = istart;
    let mut counting = [0i16; (FSE_MAX_SYMBOL_VALUE + 1) as usize];
    let mut dt = [0u32; 1 + (1 << FSE_MAX_TABLELOG)]; /* DTable_max_t */
    let mut table_log: u32 = 0;
    let mut max_symbol_value: u32 = FSE_MAX_SYMBOL_VALUE;
    let mut remaining_size = c_src_size;

    if c_src_size < 2 {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG); /* too small input size */
    }

    /* normal FSE decoding mode */
    let error_code = fse_read_ncount(
        counting.as_mut_ptr(),
        &mut max_symbol_value,
        &mut table_log,
        istart,
        c_src_size,
    );
    if fse_is_error(error_code) {
        return error_code;
    }
    if error_code >= c_src_size {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG); /* too small input size */
    }
    ip = ip.add(error_code);
    remaining_size -= error_code;

    let error_code = fse_build_dtable(
        dt.as_mut_ptr(),
        counting.as_ptr(),
        max_symbol_value,
        table_log,
    );
    if fse_is_error(error_code) {
        return error_code;
    }

    /* always return, even if it is an error code */
    fse_decompress_using_dtable(dst, max_dst_size, ip, remaining_size, dt.as_ptr())
}

/* ******************************************
 *  Huff0 : Huffman block decompression
 ********************************************/
#[repr(C)]
#[derive(Clone, Copy)]
struct HufDElt {
    byte: u8,
    nb_bits: u8,
}

/* Loop shapes and arithmetic below intentionally mirror the frozen C. */
#[allow(clippy::needless_range_loop, clippy::manual_div_ceil)]
unsafe fn huf_read_dtable(dtable: *mut u16, src: *const u8, src_size: usize) -> usize {
    let mut huff_weight = [0u8; (HUF_MAX_SYMBOL_VALUE + 1) as usize];
    let mut rank_val = [0u32; (HUF_ABSOLUTEMAX_TABLELOG + 1) as usize];
    let ip = src;
    let dt = dtable.add(1) as *mut HufDElt;

    if src_size == 0 {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }
    let mut i_size = *ip as usize;

    let o_size: usize;
    if i_size >= 128 {
        /* special header */
        if i_size >= 242 {
            /* RLE */
            const L: [usize; 14] = [1, 2, 3, 4, 7, 8, 15, 16, 31, 32, 63, 64, 127, 128];
            o_size = L[i_size - 242];
            huff_weight = [1u8; (HUF_MAX_SYMBOL_VALUE + 1) as usize];
            i_size = 0;
        } else {
            /* Incompressible */
            o_size = i_size - 127;
            i_size = (o_size + 1) / 2;
            if i_size + 1 > src_size {
                return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
            }
            let ip = ip.add(1);
            let mut n = 0usize;
            while n < o_size {
                huff_weight[n] = *ip.add(n / 2) >> 4;
                huff_weight[n + 1] = *ip.add(n / 2) & 15;
                n += 2;
            }
        }
    } else {
        /* header compressed with FSE (normal case) */
        if i_size + 1 > src_size {
            return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
        }
        /* max 255 values decoded, last one is implied */
        let decoded = fse_decompress(
            huff_weight.as_mut_ptr(),
            HUF_MAX_SYMBOL_VALUE as usize,
            ip.add(1),
            i_size,
        );
        if fse_is_error(decoded) {
            return decoded;
        }
        o_size = decoded;
    }

    /* collect weight stats */
    let mut weight_total: u32 = 0;
    for n in 0..o_size {
        if huff_weight[n] >= HUF_ABSOLUTEMAX_TABLELOG as u8 {
            return fse_error(FSE_ERROR_CORRUPTION_DETECTED);
        }
        rank_val[huff_weight[n] as usize] += 1;
        weight_total += (1u32 << huff_weight[n]) >> 1;
    }
    if weight_total == 0 {
        return fse_error(FSE_ERROR_CORRUPTION_DETECTED);
    }

    /* get last non-null symbol weight (implied, total must be 2^n) */
    let max_bits = fse_highbit32(weight_total) + 1;
    if max_bits > *dtable as u32 {
        return fse_error(FSE_ERROR_TABLELOG_TOO_LARGE); /* DTable is too small */
    }
    *dtable = max_bits as u16;
    {
        let total = 1u32 << max_bits;
        let rest = total - weight_total;
        let verif = 1u32 << fse_highbit32(rest);
        let last_weight = fse_highbit32(rest) + 1;
        if verif != rest {
            return fse_error(FSE_ERROR_CORRUPTION_DETECTED); /* last value must be a clean power of 2 */
        }
        huff_weight[o_size] = last_weight as u8;
        rank_val[last_weight as usize] += 1;
    }

    /* check tree construction validity */
    if rank_val[1] < 2 || (rank_val[1] & 1) != 0 {
        /* by construction : at least 2 elts of rank 1, must be even */
        return fse_error(FSE_ERROR_CORRUPTION_DETECTED);
    }

    /* Prepare ranks */
    let mut next_rank_start: u32 = 0;
    for n in 1..=(max_bits as usize) {
        let current = next_rank_start;
        next_rank_start += rank_val[n] << (n - 1);
        rank_val[n] = current;
    }

    /* fill DTable */
    for n in 0..=o_size {
        let w = huff_weight[n] as usize;
        let length = (1u32 << w) >> 1;
        let d = HufDElt {
            byte: n as u8,
            nb_bits: (max_bits + 1 - w as u32) as u8,
        };
        for i in rank_val[w]..(rank_val[w] + length) {
            *dt.add(i as usize) = d;
        }
        rank_val[w] += length;
    }

    i_size + 1
}

unsafe fn huf_decode_symbol(d_stream: &mut FseDStream, dt: *const HufDElt, dt_log: u32) -> u8 {
    let val = fse_look_bits_fast(d_stream, dt_log); /* note : dtLog >= 1 */
    let entry = *dt.add(val);
    fse_skip_bits(d_stream, entry.nb_bits as u32);
    entry.byte
}

/* The C decode macros: SYMBOL_1 reloads on 32-bit only when
 * HUF_MAX_TABLELOG > 12 (never here); SYMBOL_2 reloads on 32-bit. */
#[inline]
unsafe fn huf_decode_symbol_1(
    op: *mut u8,
    d_stream: &mut FseDStream,
    dt: *const HufDElt,
    dt_log: u32,
) {
    *op = huf_decode_symbol(d_stream, dt, dt_log);
    if IS_32BITS && HUF_MAX_TABLELOG > 12 {
        fse_reload_dstream(d_stream);
    }
}

#[inline]
unsafe fn huf_decode_symbol_2(
    op: *mut u8,
    d_stream: &mut FseDStream,
    dt: *const HufDElt,
    dt_log: u32,
) {
    *op = huf_decode_symbol(d_stream, dt, dt_log);
    if IS_32BITS {
        fse_reload_dstream(d_stream);
    }
}

unsafe fn huf_decompress_using_dtable(
    dst: *mut u8,
    max_dst_size: usize,
    c_src: *const u8,
    c_src_size: usize,
    dtable: *const u16,
) -> usize {
    if c_src_size < 6 {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }

    let ostart = dst;
    let mut op = ostart;
    let omax_addr = (op as usize).wrapping_add(max_dst_size);
    let olimit_addr = if max_dst_size < 15 {
        op as usize
    } else {
        omax_addr - 15
    };

    let dt = dtable.add(1) as *const HufDElt;
    let dt_log = *dtable as u32;

    /* Init */
    let length1 = fse_read_le16(c_src) as usize;
    let length2 = fse_read_le16(c_src.add(2)) as usize;
    let length3 = fse_read_le16(c_src.add(4)) as usize;
    let length4 = c_src_size
        .wrapping_sub(6)
        .wrapping_sub(length1)
        .wrapping_sub(length2)
        .wrapping_sub(length3); /* check coherency !! */
    let start1 = c_src.add(6);
    let start2 = start1.wrapping_add(length1);
    let start3 = start2.wrapping_add(length2);
    let start4 = start3.wrapping_add(length3);

    if length1 + length2 + length3 + 6 >= c_src_size {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }

    let mut bit_d1 = FseDStream {
        bit_container: 0,
        bits_consumed: 0,
        ptr: ptr::null(),
        start: ptr::null(),
    };
    let mut bit_d2 = FseDStream {
        bit_container: 0,
        bits_consumed: 0,
        ptr: ptr::null(),
        start: ptr::null(),
    };
    let mut bit_d3 = FseDStream {
        bit_container: 0,
        bits_consumed: 0,
        ptr: ptr::null(),
        start: ptr::null(),
    };
    let mut bit_d4 = FseDStream {
        bit_container: 0,
        bits_consumed: 0,
        ptr: ptr::null(),
        start: ptr::null(),
    };

    let error_code = fse_init_dstream(&mut bit_d1, start1, length1);
    if fse_is_error(error_code) {
        return error_code;
    }
    let error_code = fse_init_dstream(&mut bit_d2, start2, length2);
    if fse_is_error(error_code) {
        return error_code;
    }
    let error_code = fse_init_dstream(&mut bit_d3, start3, length3);
    if fse_is_error(error_code) {
        return error_code;
    }
    let error_code = fse_init_dstream(&mut bit_d4, start4, length4);
    if fse_is_error(error_code) {
        return error_code;
    }

    let mut reload_status = fse_reload_dstream(&mut bit_d2);

    /* 16 symbols per loop; D2-3-4 are supposed to be synchronized and finish together */
    while reload_status < FSE_DSTREAM_COMPLETED && (op as usize) < olimit_addr {
        huf_decode_symbol_1(op, &mut bit_d1, dt, dt_log);
        huf_decode_symbol_1(op.add(1), &mut bit_d2, dt, dt_log);
        huf_decode_symbol_1(op.add(2), &mut bit_d3, dt, dt_log);
        huf_decode_symbol_1(op.add(3), &mut bit_d4, dt, dt_log);
        huf_decode_symbol_2(op.add(4), &mut bit_d1, dt, dt_log);
        huf_decode_symbol_2(op.add(5), &mut bit_d2, dt, dt_log);
        huf_decode_symbol_2(op.add(6), &mut bit_d3, dt, dt_log);
        huf_decode_symbol_2(op.add(7), &mut bit_d4, dt, dt_log);
        huf_decode_symbol_1(op.add(8), &mut bit_d1, dt, dt_log);
        huf_decode_symbol_1(op.add(9), &mut bit_d2, dt, dt_log);
        huf_decode_symbol_1(op.add(10), &mut bit_d3, dt, dt_log);
        huf_decode_symbol_1(op.add(11), &mut bit_d4, dt, dt_log);
        *op.add(12) = huf_decode_symbol(&mut bit_d1, dt, dt_log);
        *op.add(13) = huf_decode_symbol(&mut bit_d2, dt, dt_log);
        *op.add(14) = huf_decode_symbol(&mut bit_d3, dt, dt_log);
        *op.add(15) = huf_decode_symbol(&mut bit_d4, dt, dt_log);

        op = op.add(16);
        reload_status = fse_reload_dstream(&mut bit_d2)
            | fse_reload_dstream(&mut bit_d3)
            | fse_reload_dstream(&mut bit_d4);
        fse_reload_dstream(&mut bit_d1);
    }

    if reload_status != FSE_DSTREAM_COMPLETED {
        /* not complete : some bitStream might be FSE_DStream_unfinished */
        return fse_error(FSE_ERROR_CORRUPTION_DETECTED);
    }

    /* tail */
    {
        let mut bit_tail = FseDStream {
            bit_container: bit_d1.bit_container, /* required in case of FSE_DStream_endOfBuffer */
            bits_consumed: bit_d1.bits_consumed,
            ptr: bit_d1.ptr,
            start: start1,
        };
        while fse_reload_dstream(&mut bit_tail) < FSE_DSTREAM_COMPLETED && (op as usize) < omax_addr
        {
            *op = huf_decode_symbol(&mut bit_tail, dt, dt_log);
            op = op.add(1);
        }

        if fse_end_of_dstream(&bit_tail) {
            return (op as usize) - (ostart as usize);
        }
    }

    if (op as usize) == omax_addr {
        return fse_error(FSE_ERROR_DST_SIZE_TOO_SMALL); /* dst buffer is full, but cSrc unfinished */
    }

    fse_error(FSE_ERROR_CORRUPTION_DETECTED)
}

unsafe fn huf_decompress(
    dst: *mut u8,
    max_dst_size: usize,
    c_src: *const u8,
    c_src_size: usize,
) -> usize {
    /* HUF_CREATE_STATIC_DTABLE(DTable, HUF_MAX_TABLELOG) */
    let mut dtable = [0u16; 1 + (1 << HUF_MAX_TABLELOG)];
    dtable[0] = HUF_MAX_TABLELOG as u16;
    let mut ip = c_src;

    let error_code = huf_read_dtable(dtable.as_mut_ptr(), c_src, c_src_size);
    if fse_is_error(error_code) {
        return error_code;
    }
    if error_code >= c_src_size {
        return fse_error(FSE_ERROR_SRC_SIZE_WRONG);
    }
    ip = ip.add(error_code);

    huf_decompress_using_dtable(
        dst,
        max_dst_size,
        ip,
        c_src_size - error_code,
        dtable.as_ptr(),
    )
}

/* ******************************************
 *  zstd v0.1 frame decoding
 ********************************************/
const ZSTD_MAGIC_NUMBER: u32 = 0xFD2FB51E; /* 3rd version : seqNb header */

const KB: usize = 1 << 10;
const BLOCKSIZE: usize = 128 * KB; /* define, for static allocation */

const MINMATCH: usize = 4;
const MLBITS: u32 = 7;
const LLBITS: u32 = 6;
const OFFBITS: u32 = 5;
const MAX_ML: u32 = (1 << MLBITS) - 1;
const MAX_LL: u32 = (1 << LLBITS) - 1;
const MAX_OFF: u32 = (1 << OFFBITS) - 1;
#[allow(dead_code)] /* part of the frozen v0.1 constant set; used only by the compressor */
const LIT_FSE_LOG: u32 = 11;
const ML_FSE_LOG: u32 = 10;
const LL_FSE_LOG: u32 = 10;
const OFF_FSE_LOG: u32 = 9;

const ZSTD_CONTENTSIZE_ERROR: u64 = 0u64.wrapping_sub(2);

const ZSTD_BLOCK_HEADER_SIZE: usize = 3;
const ZSTD_FRAME_HEADER_SIZE: usize = 4;

/* FSE_DTABLE_SIZE_U32(maxTableLog) == 1 + (1 << maxTableLog) */
const LL_DTABLE_SIZE_U32: usize = 1 + (1 << LL_FSE_LOG as usize);
const OFF_DTABLE_SIZE_U32: usize = 1 + (1 << OFF_FSE_LOG as usize);
const ML_DTABLE_SIZE_U32: usize = 1 + (1 << ML_FSE_LOG as usize);

#[inline]
unsafe fn zstd_copy4(dst: *mut u8, src: *const u8) {
    ptr::copy_nonoverlapping(src, dst, 4);
}

#[inline]
unsafe fn zstd_copy8(dst: *mut u8, src: *const u8) {
    ptr::copy_nonoverlapping(src, dst, 8);
}

unsafe fn zstd_wildcopy(dst: *mut u8, src: *const u8, length: isize) {
    let mut ip = src;
    let mut op = dst;
    let oend_addr = (op as usize).wrapping_add(length as usize);
    while (op as usize) < oend_addr {
        zstd_copy8(op, ip);
        op = op.add(8);
        ip = ip.add(8);
    }
}

#[inline]
unsafe fn zstd_read_le16(mem_ptr: *const u8) -> u16 {
    u16::from_le_bytes(ptr::read_unaligned(mem_ptr as *const [u8; 2]))
}

#[inline]
unsafe fn zstd_read_le24(mem_ptr: *const u8) -> u32 {
    zstd_read_le16(mem_ptr) as u32 + ((*mem_ptr.add(2) as u32) << 16)
}

#[inline]
unsafe fn zstd_read_be32(mem_ptr: *const u8) -> u32 {
    u32::from_be_bytes(ptr::read_unaligned(mem_ptr as *const [u8; 4]))
}

/* blockType_t */
const BT_COMPRESSED: u32 = 0;
const BT_RAW: u32 = 1;
const BT_RLE: u32 = 2;
const BT_END: u32 = 3;

struct BlockProperties {
    block_type: u32,
    orig_size: u32,
}

/// The v0.1 streaming decompression context (`dctx_t` in C).  The struct is
/// opaque to C: `zstd_v01.h` only forward-declares it, so the definition now
/// lives here.
#[repr(C)]
pub struct ZSTDv01_Dctx {
    ll_table: [u32; LL_DTABLE_SIZE_U32],
    off_table: [u32; OFF_DTABLE_SIZE_U32],
    ml_table: [u32; ML_DTABLE_SIZE_U32],
    previous_dst_end: *const u8,
    base: *const u8,
    expected: usize,
    b_type: u32,
    phase: u32,
}

unsafe fn zstdv01_getc_block_size(
    src: *const u8,
    src_size: usize,
    bp_ptr: &mut BlockProperties,
) -> usize {
    if src_size < 3 {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }

    let header_flags = *src;
    let c_size =
        (*src.add(2) as u32) + ((*src.add(1) as u32) << 8) + (((header_flags & 7) as u32) << 16);

    bp_ptr.block_type = (header_flags >> 6) as u32;
    bp_ptr.orig_size = if bp_ptr.block_type == BT_RLE {
        c_size
    } else {
        0
    };

    if bp_ptr.block_type == BT_END {
        return 0;
    }
    if bp_ptr.block_type == BT_RLE {
        return 1;
    }
    c_size as usize
}

unsafe fn zstd_copy_uncompressed_block(
    dst: *mut u8,
    max_dst_size: usize,
    src: *const u8,
    src_size: usize,
) -> usize {
    if src_size > max_dst_size {
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }
    if src_size > 0 {
        ptr::copy_nonoverlapping(src, dst, src_size);
    }
    src_size
}

unsafe fn zstd_decompress_literals(
    dst: *mut u8,
    max_dst_size: usize,
    src: *const u8,
    src_size: usize,
) -> usize {
    let oend = dst.add(max_dst_size);
    let ip = src;

    /* check : minimum 2, for litSize, +1, for content */
    if src_size <= 3 {
        return ERROR(ZstdErrorCode::CorruptionDetected);
    }

    let mut lit_size = (*ip.add(1) as usize) + ((*ip as usize) << 8);
    lit_size += (((*ip.offset(-3) as usize) >> 3) & 7) << 16; /* mmmmh.... */

    if lit_size > max_dst_size {
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }
    let op = oend.sub(lit_size);
    let error_code = huf_decompress(op, lit_size, ip.add(2), src_size - 2);
    if fse_is_error(error_code) {
        return ERROR(ZstdErrorCode::Generic);
    }
    lit_size
}

unsafe fn zstdv01_decode_literals_block(
    dst: *mut u8,
    max_dst_size: usize,
    lit_start: &mut *const u8,
    lit_size: &mut usize,
    src: *const u8,
    src_size: usize,
) -> usize {
    let istart = src;
    let mut ip = istart;
    let ostart = dst;
    let oend = ostart.add(max_dst_size);
    let mut litbp = BlockProperties {
        block_type: 0,
        orig_size: 0,
    };

    let litc_size = zstdv01_getc_block_size(src, src_size, &mut litbp);
    if ERR_isError(litc_size) {
        return litc_size;
    }
    if litc_size > src_size - ZSTD_BLOCK_HEADER_SIZE {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }
    ip = ip.add(ZSTD_BLOCK_HEADER_SIZE);

    match litbp.block_type {
        BT_RAW => {
            *lit_start = ip;
            ip = ip.add(litc_size);
            *lit_size = litc_size;
        }
        BT_RLE => {
            let rle_size = litbp.orig_size as usize;
            if rle_size > max_dst_size {
                return ERROR(ZstdErrorCode::DstSizeTooSmall);
            }
            if src_size == 0 {
                return ERROR(ZstdErrorCode::SrcSizeWrong);
            }
            if rle_size > 0 {
                ptr::write_bytes(oend.sub(rle_size), *ip, rle_size);
            }
            *lit_start = oend.sub(rle_size);
            *lit_size = rle_size;
            ip = ip.add(1);
        }
        BT_COMPRESSED => {
            let decoded_lit_size = zstd_decompress_literals(dst, max_dst_size, ip, litc_size);
            if ERR_isError(decoded_lit_size) {
                return decoded_lit_size;
            }
            *lit_start = oend.sub(decoded_lit_size);
            *lit_size = decoded_lit_size;
            ip = ip.add(litc_size);
        }
        _ => {
            /* bt_end and impossible values */
            return ERROR(ZstdErrorCode::Generic);
        }
    }

    (ip as usize) - (istart as usize)
}

#[allow(clippy::too_many_arguments)]
unsafe fn zstdv01_decode_seq_headers(
    nb_seq: &mut i32,
    dumps_ptr: &mut *const u8,
    dumps_length_ptr: &mut usize,
    dtable_ll: *mut u32,
    dtable_ml: *mut u32,
    dtable_offb: *mut u32,
    src: *const u8,
    src_size: usize,
) -> usize {
    let istart = src;
    let mut ip = istart;
    let iend_addr = (istart as usize).wrapping_add(src_size);

    /* check */
    if src_size < 5 {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }

    /* SeqHead */
    *nb_seq = zstd_read_le16(ip) as i32;
    ip = ip.add(2);
    let ll_type = (*ip >> 6) as u32;
    let off_type = ((*ip >> 4) & 3) as u32;
    let ml_type = ((*ip >> 2) & 3) as u32;
    let dumps_length: usize;
    if (*ip & 2) != 0 {
        dumps_length = (*ip.add(2) as usize) + ((*ip.add(1) as usize) << 8);
        ip = ip.add(3);
    } else {
        dumps_length = (*ip.add(1) as usize) + (((*ip as usize) & 1) << 8);
        ip = ip.add(2);
    }
    *dumps_ptr = ip;
    ip = ip.wrapping_add(dumps_length);
    *dumps_length_ptr = dumps_length;

    /* check */
    if (ip as usize) > iend_addr.wrapping_sub(3) {
        /* min : all 3 are "raw", hence no header, but at least xxLog bits per type */
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }

    /* sequences */
    {
        let mut norm = [0i16; (MAX_ML + 1) as usize]; /* assumption : MaxML >= MaxLL and MaxOff */

        /* Build DTables */
        match ll_type {
            BT_RLE => {
                fse_build_dtable_rle(dtable_ll, *ip);
                ip = ip.add(1);
            }
            BT_RAW => {
                fse_build_dtable_raw(dtable_ll, LLBITS);
            }
            _ => {
                let mut max = MAX_LL;
                let mut ll_log = 0u32;
                let header_size = fse_read_ncount(
                    norm.as_mut_ptr(),
                    &mut max,
                    &mut ll_log,
                    ip,
                    iend_addr - ip as usize,
                );
                if fse_is_error(header_size) {
                    return ERROR(ZstdErrorCode::Generic);
                }
                if ll_log > LL_FSE_LOG {
                    return ERROR(ZstdErrorCode::CorruptionDetected);
                }
                ip = ip.add(header_size);
                fse_build_dtable(dtable_ll, norm.as_ptr(), max, ll_log);
            }
        }

        match off_type {
            BT_RLE => {
                if (ip as usize) > iend_addr.wrapping_sub(2) {
                    /* min : "raw", hence no header, but at least xxLog bits */
                    return ERROR(ZstdErrorCode::SrcSizeWrong);
                }
                fse_build_dtable_rle(dtable_offb, *ip);
                ip = ip.add(1);
            }
            BT_RAW => {
                fse_build_dtable_raw(dtable_offb, OFFBITS);
            }
            _ => {
                let mut max = MAX_OFF;
                let mut off_log = 0u32;
                let header_size = fse_read_ncount(
                    norm.as_mut_ptr(),
                    &mut max,
                    &mut off_log,
                    ip,
                    iend_addr - ip as usize,
                );
                if fse_is_error(header_size) {
                    return ERROR(ZstdErrorCode::Generic);
                }
                if off_log > OFF_FSE_LOG {
                    return ERROR(ZstdErrorCode::CorruptionDetected);
                }
                ip = ip.add(header_size);
                fse_build_dtable(dtable_offb, norm.as_ptr(), max, off_log);
            }
        }

        match ml_type {
            BT_RLE => {
                if (ip as usize) > iend_addr.wrapping_sub(2) {
                    /* min : "raw", hence no header, but at least xxLog bits */
                    return ERROR(ZstdErrorCode::SrcSizeWrong);
                }
                fse_build_dtable_rle(dtable_ml, *ip);
                ip = ip.add(1);
            }
            BT_RAW => {
                fse_build_dtable_raw(dtable_ml, MLBITS);
            }
            _ => {
                let mut max = MAX_ML;
                let mut ml_log = 0u32;
                let header_size = fse_read_ncount(
                    norm.as_mut_ptr(),
                    &mut max,
                    &mut ml_log,
                    ip,
                    iend_addr - ip as usize,
                );
                if fse_is_error(header_size) {
                    return ERROR(ZstdErrorCode::Generic);
                }
                if ml_log > ML_FSE_LOG {
                    return ERROR(ZstdErrorCode::CorruptionDetected);
                }
                ip = ip.add(header_size);
                fse_build_dtable(dtable_ml, norm.as_ptr(), max, ml_log);
            }
        }
    }

    (ip as usize) - (istart as usize)
}

#[derive(Clone, Copy)]
struct Seq {
    lit_length: usize,
    offset: usize,
    match_length: usize,
}

struct SeqState {
    d_stream: FseDStream,
    state_ll: FseDState,
    state_offb: FseDState,
    state_ml: FseDState,
    prev_offset: usize,
    dumps: *const u8,
    dumps_end: *const u8,
}

unsafe fn zstd_decode_sequence(seq: &mut Seq, seq_state: &mut SeqState) {
    let mut dumps = seq_state.dumps;
    let de = seq_state.dumps_end;

    /* Literal length */
    let mut lit_length =
        fse_decode_symbol(&mut seq_state.state_ll, &mut seq_state.d_stream) as usize;
    let prev_offset = if lit_length != 0 {
        seq.offset
    } else {
        seq_state.prev_offset
    };
    seq_state.prev_offset = seq.offset;
    if lit_length == MAX_LL as usize {
        let add = if (dumps as usize) < (de as usize) {
            let v = *dumps as u32;
            dumps = dumps.add(1);
            v
        } else {
            0
        };
        if add < 255 {
            lit_length += add as usize;
        } else if (dumps as usize) <= (de as usize).wrapping_sub(3) {
            lit_length = zstd_read_le24(dumps) as usize;
            dumps = dumps.add(3);
        }
    }

    /* Offset */
    let mut offset: usize;
    {
        let offset_code =
            fse_decode_symbol(&mut seq_state.state_offb, &mut seq_state.d_stream) as u32;
        if IS_32BITS {
            fse_reload_dstream(&mut seq_state.d_stream);
        }
        let mut nb_bits = offset_code.wrapping_sub(1);
        if offset_code == 0 {
            nb_bits = 0; /* cmove */
        }
        offset = (1usize << (nb_bits & (USIZE_BITS - 1)))
            .wrapping_add(fse_read_bits(&mut seq_state.d_stream, nb_bits));
        if IS_32BITS {
            fse_reload_dstream(&mut seq_state.d_stream);
        }
        if offset_code == 0 {
            offset = prev_offset;
        }
    }

    /* MatchLength */
    let mut match_length =
        fse_decode_symbol(&mut seq_state.state_ml, &mut seq_state.d_stream) as usize;
    if match_length == MAX_ML as usize {
        let add = if (dumps as usize) < (de as usize) {
            let v = *dumps as u32;
            dumps = dumps.add(1);
            v
        } else {
            0
        };
        if add < 255 {
            match_length += add as usize;
        } else if (dumps as usize) <= (de as usize).wrapping_sub(3) {
            match_length = zstd_read_le24(dumps) as usize;
            dumps = dumps.add(3);
        }
    }
    match_length += MINMATCH;

    /* save result */
    seq.lit_length = lit_length;
    seq.offset = offset;
    seq.match_length = match_length;
    seq_state.dumps = dumps;
}

unsafe fn zstd_exec_sequence(
    op: *mut u8,
    sequence: Seq,
    lit_ptr: &mut *const u8,
    lit_limit: *const u8,
    base: *const u8,
    oend: *mut u8,
) -> usize {
    static DEC32TABLE: [usize; 8] = [0, 1, 2, 1, 4, 4, 4, 4]; /* added */
    static DEC64TABLE: [usize; 8] = [8, 8, 8, 7, 8, 9, 10, 11]; /* subtracted */
    let ostart = op;
    let mut op = op;
    let o_lit_end = op.wrapping_add(sequence.lit_length);
    let lit_length = sequence.lit_length;
    /* risk : address space overflow (32-bits) */
    let end_match = op
        .wrapping_add(lit_length)
        .wrapping_add(sequence.match_length);
    let lit_end = (*lit_ptr).wrapping_add(lit_length);

    /* checks */
    let seq_length = sequence.lit_length.wrapping_add(sequence.match_length);

    if seq_length > (oend as usize).wrapping_sub(op as usize) {
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }
    if sequence.lit_length > (lit_limit as usize).wrapping_sub(*lit_ptr as usize) {
        return ERROR(ZstdErrorCode::CorruptionDetected);
    }
    /* Now we know there are no overflow in literal nor match lengths, can use pointer checks */
    if sequence.offset > ((o_lit_end as usize).wrapping_sub(base as usize)) as u32 as usize {
        return ERROR(ZstdErrorCode::CorruptionDetected);
    }

    if (end_match as usize) > (oend as usize) {
        /* overwrite beyond dst buffer */
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }
    if (lit_end as usize) > (lit_limit as usize) {
        /* overRead beyond lit buffer */
        return ERROR(ZstdErrorCode::CorruptionDetected);
    }
    if sequence.match_length > (*lit_ptr as usize).wrapping_sub(op as usize) {
        /* overwrite literal segment */
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }

    /* copy Literals */
    /* note : v0.1 seems to allow scenarios where output or input are close to end of buffer */
    ptr::copy(*lit_ptr, op, sequence.lit_length);

    op = op.add(lit_length);
    *lit_ptr = lit_end; /* update for next sequence */

    /* check : last match must be at a minimum distance of 8 from end of dest buffer */
    if (oend as usize) - (op as usize) < 8 {
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }

    /* copy Match */
    {
        let overlap_risk = (lit_end as usize).wrapping_sub(end_match as usize) < 12;
        /* possible underflow at op - offset ? */
        let mut match_ptr = (op as usize).wrapping_sub(sequence.offset) as *const u8;
        let mut qutt: usize = 12;
        let mut saved = [0u8; 16]; /* U64 saved[2] */

        /* check */
        if (match_ptr as usize) < (base as usize) {
            return ERROR(ZstdErrorCode::CorruptionDetected);
        }
        if sequence.offset > base as usize {
            return ERROR(ZstdErrorCode::CorruptionDetected);
        }

        /* save beginning of literal sequence, in case of write overlap */
        if overlap_risk {
            if (end_match as usize).wrapping_add(qutt) > (oend as usize) {
                qutt = (oend as usize) - (end_match as usize);
            }
            ptr::copy_nonoverlapping(end_match as *const u8, saved.as_mut_ptr(), qutt);
        }

        if sequence.offset < 8 {
            let dec64 = DEC64TABLE[sequence.offset];
            *op = *match_ptr;
            *op.add(1) = *match_ptr.add(1);
            *op.add(2) = *match_ptr.add(2);
            *op.add(3) = *match_ptr.add(3);
            match_ptr = match_ptr.add(DEC32TABLE[sequence.offset]);
            zstd_copy4(op.add(4), match_ptr);
            match_ptr = match_ptr.sub(dec64);
        } else {
            zstd_copy8(op, match_ptr);
        }
        op = op.add(8);
        match_ptr = match_ptr.add(8);

        if (end_match as usize) > (oend as usize).wrapping_sub(16 - MINMATCH) {
            if (op as usize) < (oend as usize).wrapping_sub(8) {
                let dist = ((oend as usize) - 8) - (op as usize);
                zstd_wildcopy(op, match_ptr, dist as isize);
                match_ptr = match_ptr.add(dist);
                op = oend.sub(8);
            }
            while (op as usize) < (end_match as usize) {
                *op = *match_ptr;
                op = op.add(1);
                match_ptr = match_ptr.add(1);
            }
        } else {
            /* works even if matchLength < 8 */
            zstd_wildcopy(op, match_ptr, sequence.match_length as isize - 8);
        }

        /* restore, in case of overlap */
        if overlap_risk {
            ptr::copy_nonoverlapping(saved.as_ptr(), end_match, qutt);
        }
    }

    (end_match as usize) - (ostart as usize)
}

unsafe fn zstd_decompress_sequences(
    ctx: *mut ZSTDv01_Dctx,
    dst: *mut u8,
    max_dst_size: usize,
    seq_start: *const u8,
    seq_size: usize,
    lit_start: *const u8,
    lit_size: usize,
) -> usize {
    let dctx = ctx;
    let mut ip = seq_start;
    let iend_addr = (ip as usize).wrapping_add(seq_size);
    let ostart = dst;
    let mut op = ostart;
    let oend = ostart.add(max_dst_size);
    let mut lit_ptr = lit_start;
    let lit_end = lit_start.add(lit_size);
    let mut nb_seq: i32 = 0;
    let mut dumps: *const u8 = ptr::null();
    let mut dumps_length: usize = 0;
    let dtable_ll = (*dctx).ll_table.as_mut_ptr();
    let dtable_ml = (*dctx).ml_table.as_mut_ptr();
    let dtable_offb = (*dctx).off_table.as_mut_ptr();
    let base = (*dctx).base;

    /* Build Decoding Tables */
    let error_code = zstdv01_decode_seq_headers(
        &mut nb_seq,
        &mut dumps,
        &mut dumps_length,
        dtable_ll,
        dtable_ml,
        dtable_offb,
        ip,
        iend_addr - ip as usize,
    );
    if ERR_isError(error_code) {
        return error_code;
    }
    ip = ip.add(error_code);

    /* Regen sequences */
    {
        let mut sequence = Seq {
            lit_length: 0,
            offset: 0,
            match_length: 0,
        };
        let mut seq_state = SeqState {
            d_stream: FseDStream {
                bit_container: 0,
                bits_consumed: 0,
                ptr: ptr::null(),
                start: ptr::null(),
            },
            state_ll: FseDState {
                state: 0,
                table: ptr::null(),
            },
            state_offb: FseDState {
                state: 0,
                table: ptr::null(),
            },
            state_ml: FseDState {
                state: 0,
                table: ptr::null(),
            },
            prev_offset: 1,
            dumps,
            dumps_end: dumps.wrapping_add(dumps_length),
        };
        let error_code = fse_init_dstream(&mut seq_state.d_stream, ip, iend_addr - ip as usize);
        if fse_is_error(error_code) {
            return ERROR(ZstdErrorCode::CorruptionDetected);
        }
        fse_init_dstate(&mut seq_state.state_ll, &mut seq_state.d_stream, dtable_ll);
        fse_init_dstate(
            &mut seq_state.state_offb,
            &mut seq_state.d_stream,
            dtable_offb,
        );
        fse_init_dstate(&mut seq_state.state_ml, &mut seq_state.d_stream, dtable_ml);

        while fse_reload_dstream(&mut seq_state.d_stream) <= FSE_DSTREAM_COMPLETED && nb_seq > 0 {
            nb_seq -= 1;
            zstd_decode_sequence(&mut sequence, &mut seq_state);
            let one_seq_size = zstd_exec_sequence(op, sequence, &mut lit_ptr, lit_end, base, oend);
            if ERR_isError(one_seq_size) {
                return one_seq_size;
            }
            op = op.add(one_seq_size);
        }

        /* check if reached exact end */
        if !fse_end_of_dstream(&seq_state.d_stream) {
            /* requested too much : data is corrupted */
            return ERROR(ZstdErrorCode::CorruptionDetected);
        }
        if nb_seq < 0 {
            /* requested too many sequences : data is corrupted */
            return ERROR(ZstdErrorCode::CorruptionDetected);
        }

        /* last literal segment */
        {
            let last_ll_size = (lit_end as usize) - (lit_ptr as usize);
            if (op as usize).wrapping_add(last_ll_size) > (oend as usize) {
                return ERROR(ZstdErrorCode::DstSizeTooSmall);
            }
            if last_ll_size > 0 {
                if !std::ptr::eq(op as *const u8, lit_ptr) {
                    ptr::copy(lit_ptr, op, last_ll_size);
                }
                op = op.add(last_ll_size);
            }
        }
    }

    (op as usize) - (ostart as usize)
}

unsafe fn zstd_decompress_block(
    ctx: *mut ZSTDv01_Dctx,
    dst: *mut u8,
    max_dst_size: usize,
    src: *const u8,
    src_size: usize,
) -> usize {
    /* blockType == blockCompressed, srcSize is trusted */
    let mut ip = src;
    let mut lit_ptr: *const u8 = ptr::null();
    let mut lit_size: usize = 0;

    /* Decode literals sub-block */
    let error_code = zstdv01_decode_literals_block(
        dst,
        max_dst_size,
        &mut lit_ptr,
        &mut lit_size,
        src,
        src_size,
    );
    if ERR_isError(error_code) {
        return error_code;
    }
    ip = ip.add(error_code);
    let src_size = src_size - error_code;

    zstd_decompress_sequences(ctx, dst, max_dst_size, ip, src_size, lit_ptr, lit_size)
}

unsafe fn zstdv01_decompress_dctx(
    ctx: *mut ZSTDv01_Dctx,
    dst: *mut u8,
    max_dst_size: usize,
    src: *const u8,
    src_size: usize,
) -> usize {
    let mut ip = src;
    let iend_addr = (ip as usize).wrapping_add(src_size);
    let ostart = dst;
    let mut op = ostart;
    let oend_addr = (ostart as usize).wrapping_add(max_dst_size);
    let mut remaining_size = src_size;
    let mut error_code: usize = 0;

    /* Frame Header */
    if src_size < ZSTD_FRAME_HEADER_SIZE + ZSTD_BLOCK_HEADER_SIZE {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }
    let magic_number = zstd_read_be32(src);
    if magic_number != ZSTD_MAGIC_NUMBER {
        return ERROR(ZstdErrorCode::PrefixUnknown);
    }
    ip = ip.add(ZSTD_FRAME_HEADER_SIZE);
    remaining_size -= ZSTD_FRAME_HEADER_SIZE;

    /* Loop on each block */
    loop {
        let mut block_properties = BlockProperties {
            block_type: 0,
            orig_size: 0,
        };
        let block_size =
            zstdv01_getc_block_size(ip, iend_addr - ip as usize, &mut block_properties);
        if ERR_isError(block_size) {
            return block_size;
        }

        ip = ip.add(ZSTD_BLOCK_HEADER_SIZE);
        remaining_size -= ZSTD_BLOCK_HEADER_SIZE;
        if block_size > remaining_size {
            return ERROR(ZstdErrorCode::SrcSizeWrong);
        }

        match block_properties.block_type {
            BT_COMPRESSED => {
                error_code =
                    zstd_decompress_block(ctx, op, oend_addr - op as usize, ip, block_size);
            }
            BT_RAW => {
                error_code =
                    zstd_copy_uncompressed_block(op, oend_addr - op as usize, ip, block_size);
            }
            BT_RLE => {
                return ERROR(ZstdErrorCode::Generic); /* not yet supported */
            }
            BT_END => {
                /* end of frame */
                if remaining_size != 0 {
                    return ERROR(ZstdErrorCode::SrcSizeWrong);
                }
            }
            _ => {
                return ERROR(ZstdErrorCode::Generic);
            }
        }
        if block_size == 0 {
            break; /* bt_end */
        }

        if ERR_isError(error_code) {
            return error_code;
        }
        op = op.add(error_code);
        ip = ip.add(block_size);
        remaining_size -= block_size;
    }

    (op as usize) - (ostart as usize)
}

/* ZSTD_errorFrameSizeInfoLegacy() :
assumes `cSize` and `dBound` are _not_ NULL */
unsafe fn zstd_error_frame_size_info_legacy(c_size: *mut usize, d_bound: *mut u64, ret: usize) {
    *c_size = ret;
    *d_bound = ZSTD_CONTENTSIZE_ERROR;
}

/* ******************************************
 *  Exported C ABI (zstd_v01.h)
 ********************************************/

/// C ABI: `ZSTDv01_isError`.
#[no_mangle]
pub extern "C" fn ZSTDv01_isError(code: usize) -> c_uint {
    ERR_isError(code) as c_uint
}

/// C ABI: `ZSTDv01_decompressDCtx`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_decompressDCtx(
    ctx: *mut c_void,
    dst: *mut c_void,
    max_original_size: usize,
    src: *const c_void,
    compressed_size: usize,
) -> usize {
    zstdv01_decompress_dctx(
        ctx as *mut ZSTDv01_Dctx,
        dst as *mut u8,
        max_original_size,
        src as *const u8,
        compressed_size,
    )
}

/// C ABI: `ZSTDv01_decompress`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_decompress(
    dst: *mut c_void,
    max_original_size: usize,
    src: *const c_void,
    compressed_size: usize,
) -> usize {
    /* The C version uses an uninitialized on-stack dctx_t; only `base` is
     * read before being written, so a zeroed context is equivalent. */
    let mut ctx = std::mem::MaybeUninit::<ZSTDv01_Dctx>::zeroed();
    let ctx_ptr = ctx.as_mut_ptr();
    (*ctx_ptr).base = dst as *const u8;
    zstdv01_decompress_dctx(
        ctx_ptr,
        dst as *mut u8,
        max_original_size,
        src as *const u8,
        compressed_size,
    )
}

/// C ABI: `ZSTDv01_findFrameSizeInfoLegacy`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_findFrameSizeInfoLegacy(
    src: *const c_void,
    src_size: usize,
    c_size: *mut usize,
    d_bound: *mut u64,
) {
    let mut ip = src as *const u8;
    let mut remaining_size = src_size;
    let mut nb_blocks: usize = 0;

    /* Frame Header */
    if src_size < ZSTD_FRAME_HEADER_SIZE + ZSTD_BLOCK_HEADER_SIZE {
        zstd_error_frame_size_info_legacy(c_size, d_bound, ERROR(ZstdErrorCode::SrcSizeWrong));
        return;
    }
    let magic_number = zstd_read_be32(src as *const u8);
    if magic_number != ZSTD_MAGIC_NUMBER {
        zstd_error_frame_size_info_legacy(c_size, d_bound, ERROR(ZstdErrorCode::PrefixUnknown));
        return;
    }
    ip = ip.add(ZSTD_FRAME_HEADER_SIZE);
    remaining_size -= ZSTD_FRAME_HEADER_SIZE;

    /* Loop on each block */
    loop {
        let mut block_properties = BlockProperties {
            block_type: 0,
            orig_size: 0,
        };
        let block_size = zstdv01_getc_block_size(ip, remaining_size, &mut block_properties);
        if ERR_isError(block_size) {
            zstd_error_frame_size_info_legacy(c_size, d_bound, block_size);
            return;
        }

        ip = ip.add(ZSTD_BLOCK_HEADER_SIZE);
        remaining_size -= ZSTD_BLOCK_HEADER_SIZE;
        if block_size > remaining_size {
            zstd_error_frame_size_info_legacy(c_size, d_bound, ERROR(ZstdErrorCode::SrcSizeWrong));
            return;
        }

        if block_size == 0 {
            break; /* bt_end */
        }

        ip = ip.add(block_size);
        remaining_size -= block_size;
        nb_blocks += 1;
    }

    *c_size = (ip as usize) - (src as usize);
    *d_bound = (nb_blocks * BLOCKSIZE) as u64;
}

/* ******************************************
 *  Streaming Decompression API
 ********************************************/

/// C ABI: `ZSTDv01_resetDCtx`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_resetDCtx(dctx: *mut ZSTDv01_Dctx) -> usize {
    (*dctx).expected = ZSTD_FRAME_HEADER_SIZE;
    (*dctx).phase = 0;
    (*dctx).previous_dst_end = ptr::null();
    (*dctx).base = ptr::null();
    0
}

/// C ABI: `ZSTDv01_createDCtx`.  Allocated with `malloc` exactly like the C
/// implementation, so create/free may be paired across the C/Rust boundary.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_createDCtx() -> *mut ZSTDv01_Dctx {
    let dctx = libc::malloc(std::mem::size_of::<ZSTDv01_Dctx>()) as *mut ZSTDv01_Dctx;
    if dctx.is_null() {
        return ptr::null_mut();
    }
    ZSTDv01_resetDCtx(dctx);
    dctx
}

/// C ABI: `ZSTDv01_freeDCtx`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_freeDCtx(dctx: *mut ZSTDv01_Dctx) -> usize {
    libc::free(dctx as *mut c_void);
    0
}

/// C ABI: `ZSTDv01_nextSrcSizeToDecompress`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_nextSrcSizeToDecompress(dctx: *mut ZSTDv01_Dctx) -> usize {
    (*dctx).expected
}

/// C ABI: `ZSTDv01_decompressContinue`.
#[no_mangle]
pub unsafe extern "C" fn ZSTDv01_decompressContinue(
    dctx: *mut ZSTDv01_Dctx,
    dst: *mut c_void,
    max_dst_size: usize,
    src: *const c_void,
    src_size: usize,
) -> usize {
    let ctx = dctx;
    let src = src as *const u8;
    let dst = dst as *mut u8;

    /* Sanity check */
    if src_size != (*ctx).expected {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }
    if !std::ptr::eq(dst as *const u8, (*ctx).previous_dst_end) {
        /* not contiguous */
        (*ctx).base = dst as *const u8;
    }

    /* Decompress : frame header */
    if (*ctx).phase == 0 {
        /* Check frame magic header */
        let magic_number = zstd_read_be32(src);
        if magic_number != ZSTD_MAGIC_NUMBER {
            return ERROR(ZstdErrorCode::PrefixUnknown);
        }
        (*ctx).phase = 1;
        (*ctx).expected = ZSTD_BLOCK_HEADER_SIZE;
        return 0;
    }

    /* Decompress : block header */
    if (*ctx).phase == 1 {
        let mut bp = BlockProperties {
            block_type: 0,
            orig_size: 0,
        };
        let block_size = zstdv01_getc_block_size(src, ZSTD_BLOCK_HEADER_SIZE, &mut bp);
        if ERR_isError(block_size) {
            return block_size;
        }
        if bp.block_type == BT_END {
            (*ctx).expected = 0;
            (*ctx).phase = 0;
        } else {
            (*ctx).expected = block_size;
            (*ctx).b_type = bp.block_type;
            (*ctx).phase = 2;
        }

        return 0;
    }

    /* Decompress : block content */
    {
        let r_size = match (*ctx).b_type {
            BT_COMPRESSED => zstd_decompress_block(ctx, dst, max_dst_size, src, src_size),
            BT_RAW => zstd_copy_uncompressed_block(dst, max_dst_size, src, src_size),
            BT_RLE => {
                return ERROR(ZstdErrorCode::Generic); /* not yet handled */
            }
            BT_END => {
                /* should never happen (filtered at phase 1) */
                0
            }
            _ => {
                return ERROR(ZstdErrorCode::Generic);
            }
        };
        (*ctx).phase = 1;
        (*ctx).expected = ZSTD_BLOCK_HEADER_SIZE;
        if ERR_isError(r_size) {
            return r_size;
        }
        (*ctx).previous_dst_end = (dst as usize + r_size) as *const u8;
        r_size
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    /// 237-byte base text; the fixtures compress repetitions of it.
    const SAMPLE: &str = "snowden is snowed in / he's now then in his snow den / when does the snow end?\ngoodbye little dog / you dug some holes in your day / they'll be hard to fill.\nwhen life shuts a door, / just open it. it's a door. / that is how doors work.\n";

    /// `SAMPLE` repeated 3 times (711 bytes), compressed by a zstd binary
    /// built from the v0.1.0 tag.  Single compressed block (FSE + Huff0),
    /// verified byte-identical against the pristine C decoder.
    const FRAME_ENTROPY: &[u8] = &[
        0xFD, 0x2F, 0xB5, 0x1E, 0x00, 0x00, 0xB0, 0x00, 0x00, 0x93, 0x00, 0xD6, 0x19, 0x80, 0x87,
        0xB1, 0x00, 0xC0, 0x73, 0xC5, 0x8A, 0xA5, 0x6C, 0x6F, 0x4B, 0xF2, 0x9F, 0x94, 0xC4, 0x2B,
        0xE4, 0x6B, 0x2C, 0x96, 0xAE, 0x5F, 0xC8, 0x9C, 0x1F, 0x00, 0x1C, 0x00, 0x1B, 0x00, 0x43,
        0x31, 0x70, 0xE4, 0xC9, 0xA3, 0x46, 0xD9, 0xAD, 0xFD, 0x78, 0x37, 0x66, 0xA6, 0x4D, 0x15,
        0xCA, 0x33, 0xF5, 0xA7, 0x31, 0x83, 0x02, 0x96, 0x7E, 0xD0, 0x5E, 0xAC, 0xE9, 0x48, 0x03,
        0xC7, 0xEF, 0x44, 0x81, 0x0B, 0x00, 0x90, 0xEA, 0x55, 0x41, 0xD8, 0x4E, 0x36, 0x10, 0xAC,
        0x95, 0x92, 0x42, 0x5D, 0x92, 0xF4, 0x64, 0x7F, 0x96, 0x44, 0x59, 0x0B, 0x03, 0x4A, 0xF6,
        0x16, 0x9F, 0xC8, 0xB9, 0x11, 0x70, 0xB8, 0x35, 0x06, 0xC4, 0x26, 0xC7, 0x6A, 0x89, 0xE4,
        0x6F, 0x65, 0xC0, 0x9B, 0x55, 0x08, 0xEB, 0xE8, 0x37, 0x66, 0x67, 0x9E, 0x7D, 0x57, 0xA0,
        0x25, 0x0D, 0xA4, 0x3E, 0x26, 0x8F, 0x32, 0xF6, 0xC9, 0x49, 0x50, 0x40, 0x0A, 0xED, 0x34,
        0x94, 0x15, 0x5E, 0xE3, 0x1B, 0xD6, 0x27, 0x05, 0x00, 0x54, 0x05, 0x41, 0xFF, 0xD6, 0x01,
        0x00, 0x80, 0x36, 0x00, 0xFE, 0x8D, 0x38, 0x42, 0x51, 0x7E, 0x40, 0x38, 0xD5, 0x60, 0x46,
        0x03, 0x90, 0x25, 0xC0, 0x00, 0x00,
    ];

    /// 48 random bytes compressed by v0.1.0: a raw (uncompressed) block.
    const FRAME_RAW: &[u8] = &[
        0xFD, 0x2F, 0xB5, 0x1E, 0x40, 0x00, 0x30, 0x77, 0xE9, 0x9A, 0x70, 0x2F, 0x77, 0x16, 0x9A,
        0x92, 0xD4, 0xEE, 0x72, 0xFD, 0xDD, 0x0F, 0x39, 0x33, 0x8B, 0x8B, 0x3C, 0x6A, 0x91, 0xB2,
        0x2B, 0x3A, 0xF0, 0x0E, 0xA6, 0x4C, 0x51, 0xA0, 0xC9, 0x5F, 0x69, 0x1A, 0xCE, 0x93, 0x5C,
        0x7F, 0x43, 0x0C, 0xD9, 0x25, 0xBC, 0x91, 0xDD, 0x6E, 0xD7, 0xC0, 0x00, 0x00,
    ];

    const RAW_PAYLOAD: &[u8] = &[
        0x77, 0xE9, 0x9A, 0x70, 0x2F, 0x77, 0x16, 0x9A, 0x92, 0xD4, 0xEE, 0x72, 0xFD, 0xDD, 0x0F,
        0x39, 0x33, 0x8B, 0x8B, 0x3C, 0x6A, 0x91, 0xB2, 0x2B, 0x3A, 0xF0, 0x0E, 0xA6, 0x4C, 0x51,
        0xA0, 0xC9, 0x5F, 0x69, 0x1A, 0xCE, 0x93, 0x5C, 0x7F, 0x43, 0x0C, 0xD9, 0x25, 0xBC, 0x91,
        0xDD, 0x6E, 0xD7,
    ];

    /// `SAMPLE` repeated 1800 times (426600 bytes) compressed by v0.1.0:
    /// four data blocks, so it exercises multi-block frames and repeated
    /// offsets.
    const FRAME_MULTI_BLOCK: &[u8] = &[
        0xFD, 0x2F, 0xB5, 0x1E, 0x00, 0x00, 0xB0, 0x00, 0x00, 0x93, 0x00, 0xD6, 0x19, 0x80, 0x87,
        0xB1, 0x00, 0xC0, 0x73, 0xC5, 0x8A, 0xA5, 0x6C, 0x6F, 0x4B, 0xF2, 0x9F, 0x94, 0xC4, 0x2B,
        0xE4, 0x6B, 0x2C, 0x96, 0xAE, 0x5F, 0xC8, 0x9C, 0x1F, 0x00, 0x1C, 0x00, 0x1B, 0x00, 0x43,
        0x31, 0x70, 0xE4, 0xC9, 0xA3, 0x46, 0xD9, 0xAD, 0xFD, 0x78, 0x37, 0x66, 0xA6, 0x4D, 0x15,
        0xCA, 0x33, 0xF5, 0xA7, 0x31, 0x83, 0x02, 0x96, 0x7E, 0xD0, 0x5E, 0xAC, 0xE9, 0x48, 0x03,
        0xC7, 0xEF, 0x44, 0x81, 0x0B, 0x00, 0x90, 0xEA, 0x55, 0x41, 0xD8, 0x4E, 0x36, 0x10, 0xAC,
        0x95, 0x92, 0x42, 0x5D, 0x92, 0xF4, 0x64, 0x7F, 0x96, 0x44, 0x59, 0x0B, 0x03, 0x4A, 0xF6,
        0x16, 0x9F, 0xC8, 0xB9, 0x11, 0x70, 0xB8, 0x35, 0x06, 0xC4, 0x26, 0xC7, 0x6A, 0x89, 0xE4,
        0x6F, 0x65, 0xC0, 0x9B, 0x55, 0x08, 0xEB, 0xE8, 0x37, 0x66, 0x67, 0x9E, 0x7D, 0x57, 0xA0,
        0x25, 0x0D, 0xA4, 0x3E, 0x26, 0x8F, 0x32, 0xF6, 0xC9, 0x49, 0x50, 0x40, 0x0A, 0xED, 0x34,
        0x94, 0x15, 0x5E, 0xE3, 0x1B, 0xD6, 0x27, 0x05, 0x00, 0x54, 0x05, 0x41, 0xFF, 0x0F, 0xFF,
        0x01, 0x80, 0x36, 0x00, 0xFE, 0x8D, 0x38, 0x42, 0x51, 0x7E, 0x40, 0x38, 0xD5, 0x60, 0x46,
        0x03, 0x90, 0x25, 0x00, 0x00, 0x12, 0x40, 0x00, 0x00, 0x01, 0x00, 0x54, 0x04, 0xFF, 0xFC,
        0xFF, 0x01, 0x80, 0xFA, 0x7F, 0x00, 0xFC, 0x23, 0x10, 0x00, 0x00, 0x12, 0x40, 0x00, 0x00,
        0x01, 0x00, 0x54, 0x04, 0xFF, 0xFC, 0xFF, 0x01, 0x00, 0xF5, 0xFF, 0x00, 0xF8, 0x4B, 0x20,
        0x00, 0x00, 0x12, 0x40, 0x00, 0x00, 0x01, 0x00, 0x54, 0x04, 0xFF, 0x64, 0x82, 0x00, 0x80,
        0xEF, 0xFF, 0x00, 0xF0, 0x9F, 0x40, 0xC0, 0x00, 0x00,
    ];

    fn decompress(frame: &[u8], capacity: usize) -> Result<Vec<u8>, usize> {
        let mut out = vec![0u8; capacity];
        let code = unsafe {
            ZSTDv01_decompress(
                out.as_mut_ptr() as *mut c_void,
                capacity,
                frame.as_ptr() as *const c_void,
                frame.len(),
            )
        };
        if ZSTDv01_isError(code) != 0 {
            return Err(code);
        }
        out.truncate(code);
        Ok(out)
    }

    fn frame_size_info(frame: &[u8]) -> (usize, u64) {
        let mut c_size = 0usize;
        let mut d_bound = 0u64;
        unsafe {
            ZSTDv01_findFrameSizeInfoLegacy(
                frame.as_ptr() as *const c_void,
                frame.len(),
                &mut c_size,
                &mut d_bound,
            );
        }
        (c_size, d_bound)
    }

    #[test]
    fn decodes_entropy_frame_byte_identically() {
        let expected = SAMPLE.repeat(3).into_bytes();
        let out = decompress(FRAME_ENTROPY, expected.len()).unwrap();
        assert_eq!(out, expected);
    }

    #[test]
    fn decodes_raw_block_frame_byte_identically() {
        let out = decompress(FRAME_RAW, RAW_PAYLOAD.len()).unwrap();
        assert_eq!(out, RAW_PAYLOAD);
    }

    #[test]
    fn decodes_multi_block_frame_byte_identically() {
        let expected = SAMPLE.repeat(1800).into_bytes();
        assert_eq!(expected.len(), 426600);
        let out = decompress(FRAME_MULTI_BLOCK, expected.len()).unwrap();
        assert_eq!(out, expected);
    }

    #[test]
    fn reports_frame_size_info_like_c() {
        /* Values verified against the pristine C implementation. */
        assert_eq!(
            frame_size_info(FRAME_ENTROPY),
            (FRAME_ENTROPY.len(), 131072)
        );
        assert_eq!(frame_size_info(FRAME_RAW), (FRAME_RAW.len(), 131072));
        assert_eq!(
            frame_size_info(FRAME_MULTI_BLOCK),
            (FRAME_MULTI_BLOCK.len(), 524288)
        );
    }

    #[test]
    fn rejects_bad_magic_with_prefix_unknown() {
        let mut frame = FRAME_ENTROPY.to_vec();
        frame[0] ^= 0x55;
        assert_eq!(
            decompress(&frame, 1024).unwrap_err(),
            ERROR(ZstdErrorCode::PrefixUnknown)
        );
        let (c_size, d_bound) = frame_size_info(&frame);
        assert_eq!(c_size, ERROR(ZstdErrorCode::PrefixUnknown));
        assert_eq!(d_bound, ZSTD_CONTENTSIZE_ERROR);
    }

    #[test]
    fn rejects_truncated_frames_with_src_size_wrong() {
        for frame in [FRAME_ENTROPY, FRAME_RAW, FRAME_MULTI_BLOCK] {
            let truncated = &frame[..frame.len() - 1];
            assert_eq!(
                decompress(truncated, 1 << 20).unwrap_err(),
                ERROR(ZstdErrorCode::SrcSizeWrong)
            );
            assert_eq!(
                decompress(&frame[..5], 1 << 20).unwrap_err(),
                ERROR(ZstdErrorCode::SrcSizeWrong)
            );
        }
    }

    #[test]
    fn rejects_small_destination_with_dst_size_too_small() {
        /* Error codes verified against the pristine C implementation. */
        let expected_len = SAMPLE.len() * 3;
        assert_eq!(
            decompress(FRAME_ENTROPY, expected_len - 1).unwrap_err(),
            ERROR(ZstdErrorCode::DstSizeTooSmall)
        );
        assert_eq!(
            decompress(FRAME_ENTROPY, 0).unwrap_err(),
            ERROR(ZstdErrorCode::DstSizeTooSmall)
        );
        assert_eq!(
            decompress(FRAME_RAW, RAW_PAYLOAD.len() - 1).unwrap_err(),
            ERROR(ZstdErrorCode::DstSizeTooSmall)
        );
    }

    #[test]
    fn streaming_api_decodes_the_frame() {
        let expected = SAMPLE.repeat(3).into_bytes();
        let mut out = vec![0u8; expected.len()];
        let mut in_pos = 0usize;
        let mut out_pos = 0usize;
        unsafe {
            let dctx = ZSTDv01_createDCtx();
            assert!(!dctx.is_null());
            loop {
                let needed = ZSTDv01_nextSrcSizeToDecompress(dctx);
                if needed == 0 {
                    break;
                }
                assert!(in_pos + needed <= FRAME_ENTROPY.len());
                let produced = ZSTDv01_decompressContinue(
                    dctx,
                    out.as_mut_ptr().add(out_pos) as *mut c_void,
                    out.len() - out_pos,
                    FRAME_ENTROPY.as_ptr().add(in_pos) as *const c_void,
                    needed,
                );
                assert_eq!(ZSTDv01_isError(produced), 0);
                in_pos += needed;
                out_pos += produced;
            }
            assert_eq!(ZSTDv01_freeDCtx(dctx), 0);
        }
        assert_eq!(in_pos, FRAME_ENTROPY.len());
        assert_eq!(out_pos, expected.len());
        assert_eq!(out, expected);
    }

    #[test]
    fn streaming_context_reset_and_null_free() {
        unsafe {
            let dctx = ZSTDv01_createDCtx();
            assert_eq!(ZSTDv01_nextSrcSizeToDecompress(dctx), 4);
            /* bad magic through the streaming entry point */
            let bad = [0u8; 4];
            assert_eq!(
                ZSTDv01_decompressContinue(
                    dctx,
                    ptr::null_mut(),
                    0,
                    bad.as_ptr() as *const c_void,
                    4
                ),
                ERROR(ZstdErrorCode::PrefixUnknown)
            );
            /* wrong srcSize */
            assert_eq!(
                ZSTDv01_decompressContinue(
                    dctx,
                    ptr::null_mut(),
                    0,
                    bad.as_ptr() as *const c_void,
                    3
                ),
                ERROR(ZstdErrorCode::SrcSizeWrong)
            );
            assert_eq!(ZSTDv01_resetDCtx(dctx), 0);
            assert_eq!(ZSTDv01_nextSrcSizeToDecompress(dctx), 4);
            assert_eq!(ZSTDv01_freeDCtx(dctx), 0);
            assert_eq!(ZSTDv01_freeDCtx(ptr::null_mut()), 0);
        }
    }
}