zstd-rs/rust/src/zstd_compress.rs

#![allow(non_camel_case_types)]
#![allow(non_snake_case)]
#![allow(clippy::missing_safety_doc)]
#![allow(clippy::too_many_arguments)]

//! First high-level compression slice.
//!
//! The layout-independent one-shot entry point in this module drives the
//! already migrated compression leaves.  `ZSTD_compressCCtx` uses the same
//! path after a narrow C-owned context reset; the public context lifecycle
//! remains C-owned because it shares the configuration-dependent private
//! `ZSTD_CCtx_s` layout.  `ZSTD_compress2` and the complete-input simple
//! `ZSTD_compressStream2(..., ZSTD_e_end)` path dispatch through Rust while
//! retaining the C implementation for advanced and partial-stream cases.

use crate::errors::{ERR_isError, ZstdErrorCode, ERROR};
#[cfg(not(test))]
use crate::zstd_compress_api::ZSTD_compressBound;
use crate::zstd_compress_frame::{
    write_raw_block, ZSTD_rust_writeFrameHeader, ZSTD_writeLastEmptyBlock,
};
use crate::zstd_compress_params::{
    ZSTD_rust_params_adjustCParams, ZSTD_rust_params_maxNbSeq, ZSTD_rust_params_selectCParams,
    ZSTD_RUST_CPM_NO_ATTACH_DICT, ZSTD_RUST_PS_DISABLE,
};
use crate::zstd_compress_sequences::SeqDef;
use crate::zstd_compress_stats::{SeqStore_t, ZSTD_compressedBlockState_t};
use crate::zstd_compress_superblock::ZSTD_rust_compressSuperBlock;
use std::ffi::c_void;
use std::mem::{size_of, MaybeUninit};
use std::os::raw::c_int;
use std::ptr;

#[cfg(not(test))]
unsafe extern "C" {
    fn ZSTD_rust_resetCCtxForSimpleCompression(cctx: *mut c_void) -> usize;
    fn ZSTD_rust_prepareCCtxForSimpleCompression(
        cctx: *mut c_void,
        src_size: usize,
        compression_level: c_int,
    ) -> usize;
    fn ZSTD_rust_resetCCtxForSimpleCompressionSession(cctx: *mut c_void) -> usize;
    fn ZSTD_rust_markSimpleCompression2Complete(cctx: *mut c_void);
    fn ZSTD_rust_simpleCompress2Level(cctx: *const c_void) -> c_int;
    fn ZSTD_rust_simpleCompressStream2Level(cctx: *const c_void) -> c_int;
    fn ZSTD_compress2_c(
        cctx: *mut c_void,
        dst: *mut c_void,
        dst_capacity: usize,
        src: *const c_void,
        src_size: usize,
    ) -> usize;
    fn ZSTD_compressStream2_c(
        cctx: *mut c_void,
        output: *mut ZSTD_outBuffer,
        input: *mut ZSTD_inBuffer,
        end_op: c_int,
    ) -> usize;
}

const ZSTD_FAST: c_int = 1;
const ZSTD_DFAST: c_int = 2;
const ZSTD_BLOCKSIZE_MAX: usize = 1 << 17;
const ZSTD_CONTENTSIZE_UNKNOWN: u64 = u64::MAX;
const ZSTD_ROWSIZE: usize = 16;
const ZSTD_WINDOW_START_INDEX: u32 = 2;
const ZSTD_DUBT_UNSORTED_MARK: u32 = 1;
const ZSTD_INDEXOVERFLOW_MARGIN: usize = 16usize << 20;
const ZSTD_CURRENT_MAX: usize = if size_of::<usize>() == 8 {
    3500usize << 20
} else {
    2000usize << 20
};
const ZSTD_CHUNKSIZE_MAX: usize = u32::MAX as usize - ZSTD_CURRENT_MAX;
#[cfg(not(test))]
const ZSTD_E_END: c_int = 2;

#[cfg(not(test))]
#[repr(C)]
pub struct ZSTD_inBuffer {
    src: *const c_void,
    size: usize,
    pos: usize,
}

#[cfg(not(test))]
#[repr(C)]
pub struct ZSTD_outBuffer {
    dst: *mut c_void,
    size: usize,
    pos: usize,
}

/* HUF_WORKSPACE_SIZE + (MaxSeq + 2) * sizeof(unsigned), rounded up.  The
 * superblock leaf also accepts the larger pre-split workspace, so a fixed
 * 16 KiB buffer is sufficient for this first non-splitting path on both
 * supported pointer widths. */
const TMP_WORKSPACE_SIZE: usize = 16 << 10;

#[inline]
fn bitmix(mut val: u64, len: u64) -> u64 {
    val ^= val.rotate_right(49) ^ val.rotate_right(24);
    val = val.wrapping_mul(0x9FB21C651E98DF25);
    val ^= (val >> 35).wrapping_add(len);
    val = val.wrapping_mul(0x9FB21C651E98DF25);
    val ^ (val >> 28)
}

#[inline]
fn advance_hash_salt(hash_salt: u64, hash_salt_entropy: u64) -> u64 {
    bitmix(hash_salt, 8) ^ bitmix(hash_salt_entropy, 4)
}

/// Advance the row-matchfinder salt without exposing C's private match state.
#[no_mangle]
pub extern "C" fn ZSTD_rust_advanceHashSalt(hash_salt: u64, hash_salt_entropy: u64) -> u64 {
    advance_hash_salt(hash_salt, hash_salt_entropy)
}

#[inline]
fn index_too_close_to_max(next_src_base_offset: usize) -> bool {
    next_src_base_offset > ZSTD_CURRENT_MAX - ZSTD_INDEXOVERFLOW_MARGIN
}

/// Return whether a scalar C window offset is within the overflow margin.
#[no_mangle]
pub extern "C" fn ZSTD_rust_indexTooCloseToMax(next_src_base_offset: usize) -> c_int {
    index_too_close_to_max(next_src_base_offset) as c_int
}

#[inline]
fn dict_too_big(loaded_dict_size: usize) -> bool {
    loaded_dict_size > ZSTD_CHUNKSIZE_MAX
}

/// Return whether a dictionary exceeds the maximum loadable chunk size.
#[no_mangle]
pub extern "C" fn ZSTD_rust_dictTooBig(loaded_dict_size: usize) -> c_int {
    dict_too_big(loaded_dict_size) as c_int
}

#[inline]
fn reduce_table_internal(table: &mut [u32], reducer_value: u32, preserve_mark: bool) {
    debug_assert_eq!(table.len() % ZSTD_ROWSIZE, 0);
    debug_assert!(table.len() < (1usize << 31));

    /* Protect special index values < ZSTD_WINDOW_START_INDEX. */
    let reducer_threshold = reducer_value.wrapping_add(ZSTD_WINDOW_START_INDEX);
    let mut rows = table.chunks_exact_mut(ZSTD_ROWSIZE);
    for row in &mut rows {
        for cell in row {
            let value = *cell;
            *cell = if preserve_mark && value == ZSTD_DUBT_UNSORTED_MARK {
                /* Keep the btlazy2 unsorted marker across table reduction. */
                ZSTD_DUBT_UNSORTED_MARK
            } else if value < reducer_threshold {
                0
            } else {
                value.wrapping_sub(reducer_value)
            };
        }
    }
    debug_assert!(rows.into_remainder().is_empty());
}

/// Rust implementation of the C match-table reduction leaf.
///
/// The C wrappers select the ordinary or btlazy2 policy by passing a clear
/// zero/one `preserve_mark` value; `ZSTD_reduceIndex` remains C-owned.
#[no_mangle]
pub unsafe extern "C" fn ZSTD_rust_reduceTable(
    table: *mut u32,
    size: u32,
    reducer_value: u32,
    preserve_mark: c_int,
) {
    debug_assert!(!table.is_null() || size == 0);
    debug_assert_eq!(size % ZSTD_ROWSIZE as u32, 0);
    debug_assert!(size < (1u32 << 31));
    if size == 0 {
        return;
    }

    let table = unsafe { std::slice::from_raw_parts_mut(table, size as usize) };
    reduce_table_internal(table, reducer_value, preserve_mark != 0);
}

#[inline]
fn zeroed_state() -> ZSTD_compressedBlockState_t {
    /* The state contains only integer arrays and enum fields. */
    unsafe { MaybeUninit::<ZSTD_compressedBlockState_t>::zeroed().assume_init() }
}

#[inline]
fn checked_table_size(log: u32) -> Option<usize> {
    1usize.checked_shl(log)
}

#[inline]
fn ceil_log2(size: usize) -> u32 {
    if size <= 1 {
        0
    } else {
        usize::BITS - (size - 1).leading_zeros()
    }
}

/// Compress one frame using the already migrated block leaves.
///
/// This path deliberately starts a fresh match table for each 128 KiB block.
/// That keeps the Rust-owned context independent from the still-private C
/// `ZSTD_MatchState_t` window while producing ordinary zstd blocks that any
/// decoder can consume.
unsafe fn compress_frame(
    dst: *mut c_void,
    dst_capacity: usize,
    src: *const c_void,
    src_size: usize,
    compression_level: c_int,
) -> usize {
    if dst.is_null() {
        return ERROR(if dst_capacity == 0 {
            ZstdErrorCode::DstSizeTooSmall
        } else {
            ZstdErrorCode::DstBufferNull
        });
    }
    if src_size != 0 && src.is_null() {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }
    if src_size as u64 == ZSTD_CONTENTSIZE_UNKNOWN {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }

    let mut cparams = ZSTD_rust_params_selectCParams(
        compression_level,
        src_size as u64,
        0,
        ZSTD_RUST_CPM_NO_ATTACH_DICT,
    );
    cparams = ZSTD_rust_params_adjustCParams(
        cparams,
        src_size as u64,
        0,
        ZSTD_RUST_CPM_NO_ATTACH_DICT,
        ZSTD_RUST_PS_DISABLE,
    );

    let header_size = unsafe {
        ZSTD_rust_writeFrameHeader(
            dst,
            dst_capacity,
            0, /* noDictIDFlag */
            0, /* checksumFlag */
            1, /* contentSizeFlag */
            0, /* zstd frame */
            cparams.windowLog,
            src_size as u64,
            0,
        )
    };
    if ERR_isError(header_size) {
        return header_size;
    }

    if src_size == 0 {
        let empty_block = unsafe {
            ZSTD_writeLastEmptyBlock(
                dst.cast::<u8>().add(header_size).cast(),
                dst_capacity - header_size,
            )
        };
        return if ERR_isError(empty_block) {
            empty_block
        } else {
            header_size + empty_block
        };
    }

    let first_block_size = src_size.min(ZSTD_BLOCKSIZE_MAX);
    /* A table larger than the block cannot contain a useful index for this
     * independent-block path.  This also keeps one-shot small inputs from
     * allocating the table selected for a huge source-size hint. */
    let matcher_hash_log = cparams.hashLog.min(ceil_log2(first_block_size).max(6));
    let matcher_chain_log = cparams.chainLog.min(ceil_log2(first_block_size).max(6));
    let hash_size = match checked_table_size(matcher_hash_log) {
        Some(size) => size,
        None => return ERROR(ZstdErrorCode::MemoryAllocation),
    };
    let chain_size = match checked_table_size(matcher_chain_log) {
        Some(size) => size,
        None => return ERROR(ZstdErrorCode::MemoryAllocation),
    };

    let max_nb_seq =
        ZSTD_rust_params_maxNbSeq(ZSTD_BLOCKSIZE_MAX, cparams.minMatch, 0).saturating_add(1);
    let disable_literal_compression =
        c_int::from(cparams.strategy == ZSTD_FAST && cparams.targetLength > 0);
    let mut sequences = vec![SeqDef::default(); max_nb_seq];
    let mut literals = vec![0u8; ZSTD_BLOCKSIZE_MAX];
    let mut ll_codes = vec![0u8; max_nb_seq];
    let mut ml_codes = vec![0u8; max_nb_seq];
    let mut of_codes = vec![0u8; max_nb_seq];
    let mut hash_table = vec![0u32; hash_size];
    let mut chain_table = vec![0u32; chain_size];
    let mut workspace = vec![0u64; TMP_WORKSPACE_SIZE / size_of::<u64>()];
    let mut prev_block = zeroed_state();
    let mut next_block = zeroed_state();
    prev_block.rep = [1, 4, 8];
    next_block.rep = prev_block.rep;

    let seq_store = &mut SeqStore_t {
        sequencesStart: sequences.as_mut_ptr(),
        sequences: sequences.as_mut_ptr(),
        litStart: literals.as_mut_ptr(),
        lit: literals.as_mut_ptr(),
        llCode: ll_codes.as_mut_ptr(),
        mlCode: ml_codes.as_mut_ptr(),
        ofCode: of_codes.as_mut_ptr(),
        maxNbSeq: max_nb_seq,
        maxNbLit: ZSTD_BLOCKSIZE_MAX,
        longLengthType: 0,
        longLengthPos: 0,
    };

    let source = src.cast::<u8>();
    let output = dst.cast::<u8>();
    let mut input_offset = 0usize;
    let mut output_offset = header_size;
    while input_offset < src_size {
        let block_size = (src_size - input_offset).min(ZSTD_BLOCKSIZE_MAX);
        let block_src = unsafe { source.add(input_offset) };
        let block_end = unsafe { block_src.add(block_size) };

        seq_store.sequences = seq_store.sequencesStart;
        seq_store.lit = seq_store.litStart;
        seq_store.longLengthType = 0;
        seq_store.longLengthPos = 0;
        next_block.rep = prev_block.rep;

        let mut reps = prev_block.rep;
        let last_literals = if block_size < 8 {
            block_size
        } else if cparams.strategy == ZSTD_DFAST {
            unsafe {
                crate::zstd_double_fast::ZSTD_rust_compressBlock_doubleFast(
                    hash_table.as_mut_ptr(),
                    chain_table.as_mut_ptr(),
                    block_src,
                    0,
                    0,
                    matcher_hash_log,
                    matcher_chain_log,
                    cparams.minMatch,
                    cparams.windowLog,
                    (seq_store as *mut SeqStore_t).cast(),
                    reps.as_mut_ptr(),
                    block_src.cast(),
                    block_size,
                )
            }
        } else {
            unsafe {
                crate::zstd_fast::ZSTD_rust_compressBlock_fast(
                    hash_table.as_mut_ptr(),
                    block_src,
                    0,
                    0,
                    matcher_hash_log,
                    cparams.minMatch,
                    cparams.targetLength,
                    cparams.windowLog,
                    (seq_store as *mut SeqStore_t).cast(),
                    reps.as_mut_ptr(),
                    block_src.cast(),
                    block_size,
                )
            }
        };

        if last_literals > block_size {
            return ERROR(ZstdErrorCode::Generic);
        }
        let last_literal_src = unsafe { block_end.sub(last_literals) };
        if last_literals != 0 {
            unsafe {
                ptr::copy_nonoverlapping(last_literal_src, seq_store.lit, last_literals);
                seq_store.lit = seq_store.lit.add(last_literals);
            }
        }
        next_block.rep = reps;

        let last_block = u32::from(input_offset + block_size == src_size);
        let remaining_capacity = dst_capacity.saturating_sub(output_offset);
        let mut written = unsafe {
            ZSTD_rust_compressSuperBlock(
                (seq_store as *mut SeqStore_t).cast(),
                (&prev_block as *const ZSTD_compressedBlockState_t).cast(),
                (&mut next_block as *mut ZSTD_compressedBlockState_t).cast(),
                cparams.strategy,
                disable_literal_compression,
                workspace.as_mut_ptr().cast(),
                TMP_WORKSPACE_SIZE,
                0, /* BMI2 is optional; portable Rust leaf path */
                cparams.windowLog,
                0, /* no target compressed block size */
                output.add(output_offset).cast(),
                remaining_capacity,
                block_src.cast(),
                block_size,
                last_block,
            )
        };
        if ERR_isError(written) {
            return written;
        }
        if written == 0 {
            written = unsafe {
                write_raw_block(
                    output.add(output_offset),
                    remaining_capacity,
                    block_src,
                    block_size,
                    last_block,
                )
            };
            if ERR_isError(written) {
                return written;
            }
        }
        if written > remaining_capacity {
            return ERROR(ZstdErrorCode::DstSizeTooSmall);
        }
        output_offset += written;
        input_offset += block_size;
        std::mem::swap(&mut prev_block, &mut next_block);
        hash_table.fill(0);
        chain_table.fill(0);
    }

    output_offset
}

/// Simple one-shot compression entry point.
#[no_mangle]
pub unsafe extern "C" fn ZSTD_compress(
    dst: *mut c_void,
    dst_capacity: usize,
    src: *const c_void,
    src_size: usize,
    compression_level: c_int,
) -> usize {
    unsafe { compress_frame(dst, dst_capacity, src, src_size, compression_level) }
}

/// Simple explicit-context compression entry point.
///
/// The public contract deliberately ignores all advanced context parameters.
/// C performs the context reset because the private `ZSTD_CCtx_s` layout is
/// still configuration-dependent; the frame compressor itself is entirely
/// Rust-owned and does not inspect the context.
#[no_mangle]
pub unsafe extern "C" fn ZSTD_compressCCtx(
    cctx: *mut c_void,
    dst: *mut c_void,
    dst_capacity: usize,
    src: *const c_void,
    src_size: usize,
    compression_level: c_int,
) -> usize {
    if cctx.is_null() {
        return ERROR(ZstdErrorCode::Generic);
    }
    #[cfg(not(test))]
    {
        let reset = unsafe { ZSTD_rust_resetCCtxForSimpleCompression(cctx) };
        if ERR_isError(reset) {
            return reset;
        }
        let prepare =
            unsafe { ZSTD_rust_prepareCCtxForSimpleCompression(cctx, src_size, compression_level) };
        if ERR_isError(prepare) {
            return prepare;
        }
    }
    unsafe { compress_frame(dst, dst_capacity, src, src_size, compression_level) }
}

/// Stateful compression entry point during the context migration.
///
/// A context with only the ordinary frame settings is reset by the C shim and
/// compressed through the Rust frame path.  Contexts using dictionaries,
/// checksums, target-sized blocks, sequence collection, or other advanced
/// state still use the renamed C implementation until their state is moved.
#[no_mangle]
pub unsafe extern "C" fn ZSTD_compress2(
    cctx: *mut c_void,
    dst: *mut c_void,
    dst_capacity: usize,
    src: *const c_void,
    src_size: usize,
) -> usize {
    if cctx.is_null() {
        return ERROR(ZstdErrorCode::Generic);
    }

    #[cfg(test)]
    {
        unsafe { compress_frame(dst, dst_capacity, src, src_size, 3) }
    }

    #[cfg(not(test))]
    {
        let level = unsafe { ZSTD_rust_simpleCompress2Level(cctx.cast_const()) };
        if level != c_int::MIN {
            let reset = unsafe { ZSTD_rust_resetCCtxForSimpleCompressionSession(cctx) };
            if ERR_isError(reset) {
                return reset;
            }
            let prepare =
                unsafe { ZSTD_rust_prepareCCtxForSimpleCompression(cctx, src_size, level) };
            if ERR_isError(prepare) {
                return prepare;
            }
            let result = unsafe { compress_frame(dst, dst_capacity, src, src_size, level) };
            if !ERR_isError(result) {
                unsafe { ZSTD_rust_markSimpleCompression2Complete(cctx) };
            }
            return result;
        }
        unsafe { ZSTD_compress2_c(cctx, dst, dst_capacity, src, src_size) }
    }
}

/// Compress a streaming call when the complete input and a full output bound
/// are already available for the ordinary context configuration.
///
/// The C implementation remains the fallback for partial-output streaming,
/// `ZSTD_e_continue`/`ZSTD_e_flush`, dictionaries, and every advanced context
/// configuration.  The Rust path resets the C-owned session after emitting a
/// complete frame so the same context can immediately start another frame.
#[cfg(not(test))]
#[no_mangle]
pub unsafe extern "C" fn ZSTD_compressStream2(
    cctx: *mut c_void,
    output: *mut ZSTD_outBuffer,
    input: *mut ZSTD_inBuffer,
    end_op: c_int,
) -> usize {
    if cctx.is_null() || output.is_null() || input.is_null() {
        return ERROR(ZstdErrorCode::Generic);
    }

    let output_ref = unsafe { &mut *output };
    let input_ref = unsafe { &mut *input };
    if output_ref.pos > output_ref.size {
        return ERROR(ZstdErrorCode::DstSizeTooSmall);
    }
    if input_ref.pos > input_ref.size {
        return ERROR(ZstdErrorCode::SrcSizeWrong);
    }

    if end_op == ZSTD_E_END {
        let level = unsafe { ZSTD_rust_simpleCompressStream2Level(cctx.cast_const()) };
        if level != c_int::MIN {
            let src_size = input_ref.size - input_ref.pos;
            let dst_capacity = output_ref.size - output_ref.pos;
            let bound = ZSTD_compressBound(src_size);
            if !ERR_isError(bound) && dst_capacity >= bound {
                if dst_capacity != 0 && output_ref.dst.is_null() {
                    return ERROR(ZstdErrorCode::DstBufferNull);
                }
                if src_size != 0 && input_ref.src.is_null() {
                    return ERROR(ZstdErrorCode::SrcSizeWrong);
                }
                let dst = if output_ref.dst.is_null() {
                    ptr::null_mut()
                } else {
                    unsafe { output_ref.dst.cast::<u8>().add(output_ref.pos).cast() }
                };
                let src = if input_ref.src.is_null() {
                    ptr::null()
                } else {
                    unsafe { input_ref.src.cast::<u8>().add(input_ref.pos).cast() }
                };
                let result = unsafe { compress_frame(dst, dst_capacity, src, src_size, level) };
                if !ERR_isError(result) {
                    output_ref.pos += result;
                    input_ref.pos = input_ref.size;
                    return unsafe { ZSTD_rust_resetCCtxForSimpleCompressionSession(cctx) };
                }
            }
        }
    }

    unsafe { ZSTD_compressStream2_c(cctx, output, input, end_op) }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Write;
    use std::process::{Command, Stdio};

    fn system_round_trip(compressed: &[u8]) -> Option<Vec<u8>> {
        let mut child = Command::new("zstd")
            .args(["-q", "-d", "-c"])
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .stderr(Stdio::piped())
            .spawn()
            .ok()?;
        child.stdin.take()?.write_all(compressed).ok()?;
        let output = child.wait_with_output().ok()?;
        if !output.status.success() {
            panic!(
                "system zstd rejected Rust output: {}",
                String::from_utf8_lossy(&output.stderr)
            );
        }
        Some(output.stdout)
    }

    fn compress_input(input: &[u8], level: c_int) -> Vec<u8> {
        let capacity = crate::zstd_compress_api::ZSTD_compressBound(input.len());
        assert!(!ERR_isError(capacity));
        let mut output = vec![0u8; capacity];
        let written = unsafe {
            ZSTD_compress(
                output.as_mut_ptr().cast(),
                output.len(),
                input.as_ptr().cast(),
                input.len(),
                level,
            )
        };
        assert!(!ERR_isError(written));
        output.truncate(written);
        output
    }

    #[test]
    fn reduce_table_applies_threshold_and_wrapping_subtraction() {
        let mut table = [0, 1, 2, 3, 4, 5, 6, u32::MAX, 0, 0, 0, 0, 0, 0, 0, 0];
        reduce_table_internal(&mut table, 3, false);
        assert_eq!(&table[..8], &[0, 0, 0, 0, 0, 2, 3, u32::MAX - 3]);

        let mut wrapped_threshold = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
        reduce_table_internal(&mut wrapped_threshold, u32::MAX, false);
        assert_eq!(wrapped_threshold[0], 0);
        assert_eq!(wrapped_threshold[1], 2);
        assert_eq!(wrapped_threshold[15], 16);
    }

    #[test]
    fn reduce_table_preserves_only_the_btlazy2_mark() {
        let mut ordinary = [0u32; ZSTD_ROWSIZE];
        ordinary[..3].copy_from_slice(&[ZSTD_DUBT_UNSORTED_MARK, 5, 6]);
        reduce_table_internal(&mut ordinary, 3, false);
        assert_eq!(&ordinary[..3], &[0, 2, 3]);

        let mut btlazy2 = [0u32; ZSTD_ROWSIZE];
        btlazy2[..3].copy_from_slice(&[ZSTD_DUBT_UNSORTED_MARK, 5, 6]);
        reduce_table_internal(&mut btlazy2, 3, true);
        assert_eq!(&btlazy2[..3], &[ZSTD_DUBT_UNSORTED_MARK, 2, 3]);
    }

    #[test]
    fn reduce_table_processes_every_cell_in_multiple_rows() {
        let mut table = [0u32; ZSTD_ROWSIZE * 2];
        table[0] = 2;
        table[ZSTD_ROWSIZE - 1] = 8;
        table[ZSTD_ROWSIZE] = 1;
        table[ZSTD_ROWSIZE * 2 - 1] = u32::MAX;

        reduce_table_internal(&mut table, 4, false);

        assert_eq!(table[0], 0);
        assert_eq!(table[ZSTD_ROWSIZE - 1], 4);
        assert_eq!(table[ZSTD_ROWSIZE], 0);
        assert_eq!(table[ZSTD_ROWSIZE * 2 - 1], u32::MAX - 4);
    }

    #[test]
    fn bitmix_and_hash_salt_match_the_c_arithmetic() {
        assert_eq!(bitmix(0x0123_4567_89ab_cdef, 8), 0xd498_d855_4e8d_d8cb);
        assert_eq!(
            advance_hash_salt(0x0123_4567_89ab_cdef, 0xfedc_ba98_7654_3210),
            0xe5ee_f172_e5ff_3e57
        );
        assert_eq!(
            ZSTD_rust_advanceHashSalt(0x0123_4567_89ab_cdef, 0xfedc_ba98_7654_3210),
            0xe5ee_f172_e5ff_3e57
        );
    }

    #[test]
    fn index_too_close_to_max_uses_a_strict_margin_boundary() {
        let threshold = ZSTD_CURRENT_MAX - ZSTD_INDEXOVERFLOW_MARGIN;
        assert!(!index_too_close_to_max(threshold));
        assert!(index_too_close_to_max(threshold + 1));
        assert_eq!(ZSTD_rust_indexTooCloseToMax(threshold), 0);
        assert_eq!(ZSTD_rust_indexTooCloseToMax(threshold + 1), 1);
    }

    #[test]
    fn dict_too_big_uses_a_strict_chunk_size_boundary() {
        assert!(!dict_too_big(0));
        assert!(!dict_too_big(ZSTD_CHUNKSIZE_MAX));
        assert!(dict_too_big(ZSTD_CHUNKSIZE_MAX + 1));
        assert_eq!(ZSTD_rust_dictTooBig(ZSTD_CHUNKSIZE_MAX), 0);
        assert_eq!(ZSTD_rust_dictTooBig(ZSTD_CHUNKSIZE_MAX + 1), 1);
    }

    #[test]
    fn public_one_shot_abi_is_c_compatible() {
        let entry: unsafe extern "C" fn(*mut c_void, usize, *const c_void, usize, c_int) -> usize =
            ZSTD_compress;
        let context_entry: unsafe extern "C" fn(
            *mut c_void,
            *mut c_void,
            usize,
            *const c_void,
            usize,
            c_int,
        ) -> usize = ZSTD_compressCCtx;
        assert_eq!(size_of::<usize>(), size_of::<*const c_void>());
        let _ = entry;
        let _ = context_entry;
    }

    #[test]
    fn explicit_context_simple_api_matches_one_shot_path() {
        let input = b"explicit context compression remains a simple API";
        let capacity = crate::zstd_compress_api::ZSTD_compressBound(input.len());
        let mut output = vec![0u8; capacity];
        let written = unsafe {
            ZSTD_compressCCtx(
                std::ptr::dangling_mut::<c_void>(),
                output.as_mut_ptr().cast(),
                output.len(),
                input.as_ptr().cast(),
                input.len(),
                3,
            )
        };
        assert!(!ERR_isError(written));
        output.truncate(written);
        let one_shot = compress_input(input, 3);
        assert_eq!(output, one_shot);
        if let Some(restored) = system_round_trip(&output) {
            assert_eq!(restored, input);
        }
    }

    #[test]
    fn one_shot_round_trip_across_block_boundaries() {
        let mut input = Vec::with_capacity(128 * 1024 + 37);
        for index in 0..(128 * 1024 + 37) {
            input.push(((index * 17) ^ (index / 31)) as u8);
        }

        let compressed = compress_input(&input, 3);
        if let Some(restored) = system_round_trip(&compressed) {
            assert_eq!(restored, input);
        }
    }

    #[test]
    fn empty_and_short_inputs_have_valid_frames() {
        for input in [b"".as_slice(), b"a", b"abcdefg", b"abcdefgh"] {
            let compressed = compress_input(input, 1);
            if let Some(restored) = system_round_trip(&compressed) {
                assert_eq!(restored, input);
            }
        }
    }

    #[test]
    fn public_error_paths_match_size_t_error_contract() {
        let mut output = [0u8; 64];
        let source = [1u8; 8];
        assert_eq!(
            unsafe {
                ZSTD_compress(
                    output.as_mut_ptr().cast(),
                    0,
                    source.as_ptr().cast(),
                    source.len(),
                    3,
                )
            },
            ERROR(ZstdErrorCode::DstSizeTooSmall)
        );
        assert_eq!(
            unsafe { ZSTD_compress(ptr::null_mut(), 1, source.as_ptr().cast(), source.len(), 3) },
            ERROR(ZstdErrorCode::DstBufferNull)
        );
        assert_eq!(
            unsafe { ZSTD_compress(output.as_mut_ptr().cast(), output.len(), ptr::null(), 1, 3) },
            ERROR(ZstdErrorCode::SrcSizeWrong)
        );
    }
}