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Align deflateParams() and its documentation in zlib.h.

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This updates the documentation to reflect the behavior of
deflateParams() when it is not able to compress all of the input
data provided so far due to insufficient output space.  It also
assures that data provided is compressed before the parameter
changes, even if at the beginning of the stream.
This commit is contained in:
Mark Adler 2015-08-02 00:02:07 -07:00
parent b4ce6caf09
commit 43bfaba3d7
2 changed files with 25 additions and 12 deletions
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3
deflate.c
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@ -509,8 +509,7 @@ int ZEXPORT deflateParams(strm, level, strategy)
} }
func = configuration_table[s->level].func; func = configuration_table[s->level].func;
if ((strategy != s->strategy || func != configuration_table[level].func) && if ((strategy != s->strategy || func != configuration_table[level].func)) {
strm->total_in != 0) {
/* Flush the last buffer: */ /* Flush the last buffer: */
err = deflate(strm, Z_BLOCK); err = deflate(strm, Z_BLOCK);
if (err == Z_BUF_ERROR && s->pending == 0) if (err == Z_BUF_ERROR && s->pending == 0)

34
zlib.h
View File

@ -670,20 +670,34 @@ ZEXTERN int ZEXPORT deflateParams OF((z_streamp strm,
int strategy)); int strategy));
/* /*
Dynamically update the compression level and compression strategy. The Dynamically update the compression level and compression strategy. The
interpretation of level and strategy is as in deflateInit2. This can be interpretation of level and strategy is as in deflateInit2(). This can be
used to switch between compression and straight copy of the input data, or used to switch between compression and straight copy of the input data, or
to switch to a different kind of input data requiring a different strategy. to switch to a different kind of input data requiring a different strategy.
If the compression level is changed, the input available so far is If the compression approach (which is a function of the level) or the
compressed with the old level (and may be flushed); the new level will take strategy is changed, then the input available so far is compressed with the
effect only at the next call of deflate(). old level and strategy using deflate(strm, Z_BLOCK). There are three
approaches for the compression levels 0, 1..3, and 4..9 respectively. The
new level and strategy will take effect at the next call of deflate().
Before the call of deflateParams, the stream state must be set as for If a deflate(strm, Z_BLOCK) is performed by deflateParams(), and it does
a call of deflate(), since the currently available input may have to be not have enough output space to complete, then the parameter change will
compressed and flushed. In particular, strm->avail_out must be non-zero. take effect at an undetermined location in the uncompressed data provided so
far. In order to assure a change in the parameters at a specific location
in the uncompressed data, the deflate stream should first be flushed with
Z_BLOCK or another flush parameter, and deflate() called until
strm.avail_out is not zero, before the call of deflateParams(). Then no
more input data should be provided before the deflateParams() call. If this
is done, the old level and strategy will be applied to the data compressed
before deflateParams(), and the new level and strategy will be applied to
the the data compressed after deflateParams().
deflateParams returns Z_OK if success, Z_STREAM_ERROR if the source deflateParams returns Z_OK if success, Z_STREAM_ERROR if the source stream
stream state was inconsistent or if a parameter was invalid, Z_BUF_ERROR if state was inconsistent or if a parameter was invalid, or Z_BUF_ERROR if
strm->avail_out was zero. there was not enough output space to complete the compression before the
parameters were changed. Note that in the case of a Z_BUF_ERROR, the
parameters are changed nevertheless, and will take effect at an undetermined
location in the previously supplied uncompressed data. Compression may
proceed after a Z_BUF_ERROR.
*/ */
ZEXTERN int ZEXPORT deflateTune OF((z_streamp strm, ZEXTERN int ZEXPORT deflateTune OF((z_streamp strm,