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Expose dictCtx Functionality in LZ4

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This commit is contained in:
W. Felix Handte 2018-04-11 16:04:24 -04:00
parent 21f0c9700b
commit afa52c9b95
3 changed files with 33 additions and 2 deletions
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4
lib/lz4.c
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@ -1191,6 +1191,10 @@ int LZ4_loadDict (LZ4_stream_t* LZ4_dict, const char* dictionary, int dictSize)
return dict->dictSize;
}
void LZ4_attach_dictionary(LZ4_stream_t *working_stream, const LZ4_stream_t *dictionary_stream) {
working_stream->internal_donotuse.dictCtx = dictionary_stream != NULL ? &(dictionary_stream->internal_donotuse) : NULL;
}
static void LZ4_renormDictT(LZ4_stream_t_internal* LZ4_dict, const BYTE* src)
{

28
lib/lz4.h
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@ -386,6 +386,34 @@ LZ4LIB_API void LZ4_resetStream_fast (LZ4_stream_t* streamPtr);
*/
LZ4LIB_API int LZ4_compress_fast_extState_fastReset (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
/*! LZ4_attach_dictionary() :
* This is an experimental API that allows for the efficient use of a
* static dictionary many times.
*
* Rather than re-loading the dictionary buffer into a working context before
* each compression, or copying a pre-loaded dictionary's LZ4_stream_t into a
* working LZ4_stream_t, this function introduces a no-copy setup mechanism,
* in which the working stream references the dictionary stream in-place.
*
* Several assumptions are made about the state of the dictionary stream.
* Currently, only streams which have been prepared by LZ4_loadDict() should
* be expected to work.
*
* Alternatively, the provided dictionary stream pointer may be NULL, in which
* case any existing dictionary stream is unset.
*
* If a dictionary is provided, it replaces any pre-existing stream history.
* The dictionary contents are the only history that can be referenced and
* logically immediately precede the data compressed in the first subsequent
* compression call.
*
* The dictionary will only remain attached to the working stream through the
* first compression call, at the end of which it is cleared. The dictionary
* stream (and source buffer) must remain in-place / accessible / unchanged
* through the completion of the first compression call on the stream.
*/
LZ4LIB_API void LZ4_attach_dictionary(LZ4_stream_t *working_stream, const LZ4_stream_t *dictionary_stream);
/*-************************************
* Private definitions

3
lib/lz4frame.c
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@ -533,8 +533,7 @@ static void LZ4F_applyCDict(void* ctx,
LZ4_stream_t_internal* internal_ctx = &((LZ4_stream_t *)ctx)->internal_donotuse;
assert(!internal_ctx->initCheck);
LZ4_resetStream_fast((LZ4_stream_t *)ctx);
/* Point to the dictionary context */
internal_ctx->dictCtx = cdict ? &(cdict->fastCtx->internal_donotuse) : NULL;
LZ4_attach_dictionary((LZ4_stream_t *)ctx, cdict ? cdict->fastCtx : NULL);
} else {
if (cdict) {
memcpy(ctx, cdict->HCCtx, sizeof(*cdict->HCCtx));