Support negative Zstd compression levels#2874
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OPT_COMPRESSION_LEVEL treated any value below 1 as "use the default",
so negative Zstd levels (e.g. -5) were silently replaced with the
default level 3. Zstd supports negative ("fast") compression levels,
so only 0 (the ecalloc default and Zstd's own "use default" sentinel)
should now map to the default; negative values are passed through to
ZSTD_compress, which clamps extreme values to ZSTD_minCLevel()
internally.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
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The change is fine. Not sure we can merge it before phpredis 7.0 though. If many people are relying on |
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Summary
OPT_COMPRESSION_LEVELtreated any value below1as "use the default", so negative Zstd levels (e.g.-5) were silently discarded and replaced with the default level 3. Zstd supports negative ("fast") compression levels, so they should be honored.This changes the guard in the
REDIS_COMPRESSION_ZSTDbranch ofredis_compress()fromcompression_level < 1tocompression_level == 0:0— theecallocdefault and Zstd's own "use default" sentinel — still maps toZSTD_CLEVEL_DEFAULT(or3).ZSTD_compress().No lower-bound clamp is added:
ZSTD_compress()already clamps extreme negatives toZSTD_minCLevel()internally, andZSTD_minCLevel()only exists since libzstd 1.3.6 while phpredis supports ≥ 1.3.0 (config.m4), so calling it would break the build on older libzstd. The existing upper-bound clamp toZSTD_maxCLevel()is unchanged.Before
After