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Expand on the deflate strategy parameter in zlib.h.

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Mark Adler 2024-02-07 10:48:55 -08:00
parent e342bb3dae
commit 96d3e9e3dd
1 changed files with 15 additions and 12 deletions
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27
zlib.h
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@ -587,18 +587,21 @@ ZEXTERN int ZEXPORT deflateInit2(z_streamp strm,
The strategy parameter is used to tune the compression algorithm. Use the
value Z_DEFAULT_STRATEGY for normal data, Z_FILTERED for data produced by a
filter (or predictor), Z_HUFFMAN_ONLY to force Huffman encoding only (no
string match), or Z_RLE to limit match distances to one (run-length
encoding). Filtered data consists mostly of small values with a somewhat
random distribution. In this case, the compression algorithm is tuned to
compress them better. The effect of Z_FILTERED is to force more Huffman
coding and less string matching; it is somewhat intermediate between
Z_DEFAULT_STRATEGY and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as
fast as Z_HUFFMAN_ONLY, but give better compression for PNG image data. The
strategy parameter only affects the compression ratio but not the
correctness of the compressed output even if it is not set appropriately.
Z_FIXED prevents the use of dynamic Huffman codes, allowing for a simpler
decoder for special applications.
filter (or predictor), Z_RLE to limit match distances to one (run-length
encoding), or Z_HUFFMAN_ONLY to force Huffman encoding only (no string
matching). Filtered data consists mostly of small values with a somewhat
random distribution, as produced by the PNG filters. In this case, the
compression algorithm is tuned to compress them better. The effect of
Z_FILTERED is to force more Huffman coding and less string matching than the
default; it is intermediate between Z_DEFAULT_STRATEGY and Z_HUFFMAN_ONLY.
Z_RLE is almost as fast as Z_HUFFMAN_ONLY, but should give better
compression for PNG image data than Huffman only. The degree of string
matching from most to none is: Z_DEFAULT_STRATEGY, Z_FILTERED, Z_RLE, then
Z_HUFFMAN. The strategy parameter affects the compression ratio but never
the correctness of the compressed output, even if it is not set optimally
for the given data. Z_FIXED uses the default string matching, but prevents
the use of dynamic Huffman codes, allowing for a simpler decoder for special
applications.
deflateInit2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
memory, Z_STREAM_ERROR if any parameter is invalid (such as an invalid