This introduces GZIP_DEFAULT_LEVEL macro so that builders can easily change it by overriding (e.g. "-DGZIP_DEFAULT_LEVEL=8").
Currently, this patch is ugly. I apologize. (Because I utilize a lot of preprocessor tricks in order to implement a build-time constant table lookup.) This is how I proposed letting the user change the compression level when GZIP_LEVELS is turned off, when discussing about gzip default compression level. This patch is a proof of concept of that. <http://lists.busybox.net/pipermail/busybox/2019-September/087442.html> Signed-off-by: Kang-Che Sung <explore...@gmail.com> --- archival/gzip.c | 50 ++++++++++++++++++++++++++++++++++++------------- 1 file changed, 37 insertions(+), 13 deletions(-) diff --git a/archival/gzip.c b/archival/gzip.c index 3966a06b4..10cf2f884 100644 --- a/archival/gzip.c +++ b/archival/gzip.c @@ -251,6 +251,17 @@ typedef unsigned IPos; * save space in the various tables. IPos is used only for parameter passing. */ +#define LEVEL_CONFIG_LIST \ + /* (level, good, chain_shift, lazy, nice) */ \ + LEVEL_CONFIG_DEFINE(4, 4, 4, 4, 16) \ + LEVEL_CONFIG_DEFINE(5, 8, 5, 16, 32) \ + LEVEL_CONFIG_DEFINE(6, 8, 7, 16, 128) \ + LEVEL_CONFIG_DEFINE(7, 8, 8, 32, 128) \ + LEVEL_CONFIG_DEFINE(8, 32, 10, 128, 258) \ + LEVEL_CONFIG_DEFINE(9, 32, 12, 258, 258) + +#define GZIP_DEFAULT_LEVEL 6 + enum { WINDOW_SIZE = 2 * WSIZE, /* window size, 2*WSIZE except for MMAP or BIG_MEM, where it is the @@ -258,14 +269,25 @@ enum { */ #if !ENABLE_FEATURE_GZIP_LEVELS +# define LEVEL_CONFIG_DEFINE(level, good, chain_shift, lazy, nice) \ + l##level##_chain = (1 << (chain_shift)), \ + l##level##_lazy = (lazy), \ + l##level##_good = (good), \ + l##level##_nice = (nice), + + LEVEL_CONFIG_LIST + +# define LEVEL_CONFIG_(level, suffix) l##level##suffix +# define LEVEL_CONFIG(level, name) LEVEL_CONFIG_(level, _##name) + + comp_level_minus4 = (GZIP_DEFAULT_LEVEL - 4), - comp_level_minus4 = 6 - 4, - max_chain_length = 128, + max_chain_length = LEVEL_CONFIG(GZIP_DEFAULT_LEVEL, chain), /* To speed up deflation, hash chains are never searched beyond this length. * A higher limit improves compression ratio but degrades the speed. */ - max_lazy_match = 16, + max_lazy_match = LEVEL_CONFIG(GZIP_DEFAULT_LEVEL, lazy), /* Attempt to find a better match only when the current match is strictly * smaller than this value. This mechanism is used only for compression * levels >= 4. @@ -277,7 +299,7 @@ enum { * max_insert_length is used only for compression levels <= 3. */ - good_match = 8, + good_match = LEVEL_CONFIG(GZIP_DEFAULT_LEVEL, good), /* Use a faster search when the previous match is longer than this */ /* Values for max_lazy_match, good_match and max_chain_length, depending on @@ -286,12 +308,16 @@ enum { * found for specific files. */ - nice_match = 128, /* Stop searching when current match exceeds this */ + nice_match = LEVEL_CONFIG(GZIP_DEFAULT_LEVEL, nice) +/* Stop searching when current match exceeds this */ /* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4 * For deflate_fast() (levels <= 3) good is ignored and lazy has a different * meaning. */ -#endif /* ENABLE_FEATURE_GZIP_LEVELS */ +# undef LEVEL_CONFIG_DEFINE +# undef LEVEL_CONFIG_ +# undef LEVEL_CONFIG +#endif /* !ENABLE_FEATURE_GZIP_LEVELS */ }; struct globals { @@ -2204,12 +2230,10 @@ int gzip_main(int argc UNUSED_PARAM, char **argv) uint8_t lazy2; uint8_t nice2; } gzip_level_config[6] = { - {4, 4, 4/2, 16/2}, /* Level 4 */ - {8, 5, 16/2, 32/2}, /* Level 5 */ - {8, 7, 16/2, 128/2}, /* Level 6 */ - {8, 8, 32/2, 128/2}, /* Level 7 */ - {32, 10, 128/2, 258/2}, /* Level 8 */ - {32, 12, 258/2, 258/2}, /* Level 9 */ +# define LEVEL_CONFIG_DEFINE(level, good, chain_shift, lazy, nice) \ + {(good), (chain_shift), (lazy)/2, (nice)/2}, + LEVEL_CONFIG_LIST +# undef LEVEL_CONFIG_DEFINE }; #endif @@ -2229,7 +2253,7 @@ int gzip_main(int argc UNUSED_PARAM, char **argv) #if ENABLE_FEATURE_GZIP_LEVELS opt >>= (BBUNPK_OPTSTRLEN IF_FEATURE_GZIP_DECOMPRESS(+ 2) + 1); /* drop cfkvq[dt]n bits */ if (opt == 0) - opt = 1 << 5; /* default: 6 */ + opt = 1 << (GZIP_DEFAULT_LEVEL - 1); opt = ffs(opt >> 4); /* Maps -1..-4 to [0], -5 to [1] ... -9 to [5] */ comp_level_minus4 = opt; -- 2.18.0 _______________________________________________ busybox mailing list busybox@busybox.net http://lists.busybox.net/mailman/listinfo/busybox
