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clarified comments on ZSTD_compressContinue()

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This commit is contained in:
Yann Collet
2016-06-21 11:54:03 +02:00
parent d4f38d0dcd
commit a49e066b26
1 changed files with 17 additions and 10 deletions
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lib/common/zstd.h
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@@ -132,7 +132,7 @@ ZSTDLIB_API size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t dstCapa
/*! ZSTD_compress_usingDict() :
* Compression using a pre-defined Dictionary content (see dictBuilder).
* Note 1 : This function load the dictionary, resulting in a significant startup time.
* Note 2 : `dict` must remain valid and unmodified during compression operation.
* Note 2 : `dict` must remain accessible and unmodified during compression operation.
* Note 3 : `dict` can be `NULL`, in which case, it's equivalent to ZSTD_compressCCtx() */
ZSTDLIB_API size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
void* dst, size_t dstCapacity,
@@ -144,7 +144,7 @@ ZSTDLIB_API size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
* Decompression using a pre-defined Dictionary content (see dictBuilder).
* Dictionary must be identical to the one used during compression.
* Note 1 : This function load the dictionary, resulting in a significant startup time
* Note 2 : `dict` must remain valid and unmodified during compression operation.
* Note 2 : `dict` must remain accessible and unmodified during compression operation.
* Note 3 : `dict` can be `NULL`, in which case, it's equivalent to ZSTD_decompressDCtx() */
ZSTDLIB_API size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
void* dst, size_t dstCapacity,
@@ -192,7 +192,7 @@ ZSTDLIB_API size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
/* ====================================================================================
* The definitions in this section are considered experimental.
* They should never be used in association with a dynamic library, as they may change in the future.
* They should never be used with a dynamic library, as they may change in the future.
* They are provided for advanced usages.
* Use them only in association with static linking.
* ==================================================================================== */
@@ -322,15 +322,22 @@ ZSTDLIB_API size_t ZSTD_compressEnd(ZSTD_CCtx* cctx, void* dst, size_t dstCapaci
It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
Then, consume your input using ZSTD_compressContinue().
ZSTD_compressContinue() presumes prior data is still accessible and unmodified (up to maximum distance size, see WindowLog).
The interface is synchronous, so input will be entirely consumed and produce associated compressed output.
You must ensure there is enough space in destination buffer to store compressed data under worst case scenario.
Worst case evaluation is provided by ZSTD_compressBound().
There are some important considerations to keep in mind when using this advanced function :
- ZSTD_compressContinue() has no internal buffer. It uses externally provided buffer only.
- Interface is synchronous : input will be entirely consumed and produce 1+ compressed blocks.
- Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
Worst case evaluation is provided by ZSTD_compressBound().
ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
- ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
- ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
In which case, it will "discard" the relevant memory section from its history.
Finish a frame with ZSTD_compressEnd(), which will write the epilogue.
Without epilogue, frames will be considered unfinished (broken) by decoders.
You can then reuse ZSTD_CCtx to compress some new frame.
You can then reuse `ZSTD_CCtx` (ZSTD_compressBegin()) to compress some new frame.
*/
typedef struct {
@@ -357,7 +364,7 @@ ZSTDLIB_API size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t ds
A ZSTD_DCtx object can be re-used multiple times.
First optional operation is to retrieve frame parameters, using ZSTD_getFrameParams(), which doesn't consume the input.
It can provide the minimum size of rolling buffer required to properly decompress data,
It can provide the minimum size of rolling buffer required to properly decompress data (`windowSize`),
and optionally the final size of uncompressed content.
(Note : content size is an optional info that may not be present. 0 means : content size unknown)
Frame parameters are extracted from the beginning of compressed frame.
@@ -373,7 +380,7 @@ ZSTDLIB_API size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t ds
Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
ZSTD_nextSrcSizeToDecompress() tells how much bytes to provide as 'srcSize' to ZSTD_decompressContinue().
ZSTD_decompressContinue() requires this exact amount of bytes, or it will fail.
ZSTD_decompressContinue() needs previous data blocks during decompression, up to (1 << windowlog).
ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize`.
They should preferably be located contiguously, prior to current block. Alternatively, a round buffer is also possible.
@result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).