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Add deflateGetDictionary() function.

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Per request, but its utility is likely to be very limited. See the
comments in zlib.h.
This commit is contained in:
Mark Adler 2016-12-30 16:29:56 -08:00
parent feafcfaa05
commit ee7d7b5dda
2 changed files with 43 additions and 0 deletions
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21
deflate.c
View File

@ -440,6 +440,27 @@ int ZEXPORT deflateSetDictionary (strm, dictionary, dictLength)
return Z_OK;
}
/* ========================================================================= */
int ZEXPORT deflateGetDictionary (strm, dictionary, dictLength)
z_streamp strm;
Bytef *dictionary;
uInt *dictLength;
{
deflate_state *s;
if (deflateStateCheck(strm))
return Z_STREAM_ERROR;
s = strm->state;
uInt len = s->strstart + s->lookahead;
if (len > s->w_size)
len = s->w_size;
if (dictionary != Z_NULL && len)
zmemcpy(dictionary, s->window + s->strstart + s->lookahead - len, len);
if (dictLength != Z_NULL)
*dictLength = len;
return Z_OK;
}
/* ========================================================================= */
int ZEXPORT deflateResetKeep (strm)
z_streamp strm;

22
zlib.h
View File

@ -651,6 +651,28 @@ ZEXTERN int ZEXPORT deflateSetDictionary OF((z_streamp strm,
not perform any compression: this will be done by deflate().
*/
ZEXTERN int ZEXPORT deflateGetDictionary OF((z_streamp strm,
Bytef *dictionary,
uInt *dictLength));
/*
Returns the sliding dictionary being maintained by deflate. dictLength is
set to the number of bytes in the dictionary, and that many bytes are copied
to dictionary. dictionary must have enough space, where 32768 bytes is
always enough. If deflateGetDictionary() is called with dictionary equal to
Z_NULL, then only the dictionary length is returned, and nothing is copied.
Similary, if dictLength is Z_NULL, then it is not set.
deflateGetDictionary() may return a length less than the window size, even
when more than the window size in input has been provided. It may return up
to 258 bytes less in that case, due to how zlib's implementation of deflate
manages the sliding window and lookahead for matches, where matches can be
up to 258 bytes long. If the application needs the last window-size bytes of
input, then that would need to be saved by the application outside of zlib.
deflateGetDictionary returns Z_OK on success, or Z_STREAM_ERROR if the
stream state is inconsistent.
*/
ZEXTERN int ZEXPORT deflateCopy OF((z_streamp dest,
z_streamp source));
/*