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gzip: set compression flags correctly as per standard

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With this change and CONFIG_GZIP_FAST=2, CONFIG_FEATURE_GZIP_LEVELS=y,

GNU gzip and BusyBox gzip now produce identical output at each compression
level (excluding 1..3, as BusyBox does not implement these levels).

Signed-off-by: Daniel Edgecumbe <git@esotericnonsense.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Daniel Edgecumbe
2019-09-02 22:05:26 +01:00
committed by Denys Vlasenko
parent de82f0b764
commit ca5d86d52c
1 changed files with 18 additions and 8 deletions
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26
archival/gzip.c
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@@ -259,6 +259,7 @@ enum {
#if !ENABLE_FEATURE_GZIP_LEVELS #if !ENABLE_FEATURE_GZIP_LEVELS
comp_level = 9,
max_chain_length = 4096, max_chain_length = 4096,
/* To speed up deflation, hash chains are never searched beyond this length. /* To speed up deflation, hash chains are never searched beyond this length.
* A higher limit improves compression ratio but degrades the speed. * A higher limit improves compression ratio but degrades the speed.
@@ -334,14 +335,16 @@ struct globals {
#define head (G1.prev + WSIZE) /* hash head (see deflate.c) */ #define head (G1.prev + WSIZE) /* hash head (see deflate.c) */
#if ENABLE_FEATURE_GZIP_LEVELS #if ENABLE_FEATURE_GZIP_LEVELS
unsigned comp_level;
unsigned max_chain_length; unsigned max_chain_length;
unsigned max_lazy_match; unsigned max_lazy_match;
unsigned good_match; unsigned good_match;
unsigned nice_match; unsigned nice_match;
#define comp_level (G1.comp_level)
#define max_chain_length (G1.max_chain_length) #define max_chain_length (G1.max_chain_length)
#define max_lazy_match (G1.max_lazy_match) #define max_lazy_match (G1.max_lazy_match)
#define good_match (G1.good_match) #define good_match (G1.good_match)
#define nice_match (G1.nice_match) #define nice_match (G1.nice_match)
#endif #endif
/* =========================================================================== */ /* =========================================================================== */
@@ -1919,7 +1922,7 @@ static void bi_init(void)
/* =========================================================================== /* ===========================================================================
* Initialize the "longest match" routines for a new file * Initialize the "longest match" routines for a new file
*/ */
static void lm_init(unsigned *flags16p) static void lm_init(void)
{ {
unsigned j; unsigned j;
@@ -1927,8 +1930,6 @@ static void lm_init(unsigned *flags16p)
memset(head, 0, HASH_SIZE * sizeof(*head)); memset(head, 0, HASH_SIZE * sizeof(*head));
/* prev will be initialized on the fly */ /* prev will be initialized on the fly */
/* speed options for the general purpose bit flag */
*flags16p |= 2; /* FAST 4, SLOW 2 */
/* ??? reduce max_chain_length for binary files */ /* ??? reduce max_chain_length for binary files */
//G1.strstart = 0; // globals are zeroed in pack_gzip() //G1.strstart = 0; // globals are zeroed in pack_gzip()
@@ -2076,10 +2077,16 @@ static void zip(void)
bi_init(); bi_init();
ct_init(); ct_init();
deflate_flags = 0; /* pkzip -es, -en or -ex equivalent */ lm_init();
lm_init(&deflate_flags);
put_16bit(deflate_flags | 0x300); /* extra flags. OS id = 3 (Unix) */ deflate_flags = 0x300; /* extra flags. OS id = 3 (Unix) */
#if ENABLE_FEATURE_GZIP_LEVELS
/* Note that comp_level < 4 do not exist in this version of gzip */
if (comp_level == 9) {
deflate_flags |= 0x02; /* SLOW flag */
}
#endif
put_16bit(deflate_flags);
/* The above 32-bit misaligns outbuf (10 bytes are stored), flush it */ /* The above 32-bit misaligns outbuf (10 bytes are stored), flush it */
flush_outbuf_if_32bit_optimized(); flush_outbuf_if_32bit_optimized();
@@ -2224,6 +2231,9 @@ int gzip_main(int argc UNUSED_PARAM, char **argv)
if (opt == 0) if (opt == 0)
opt = 1 << 5; /* default: 6 */ opt = 1 << 5; /* default: 6 */
opt = ffs(opt >> 4); /* Maps -1..-4 to [0], -5 to [1] ... -9 to [5] */ opt = ffs(opt >> 4); /* Maps -1..-4 to [0], -5 to [1] ... -9 to [5] */
comp_level = opt + 4;
max_chain_length = 1 << gzip_level_config[opt].chain_shift; max_chain_length = 1 << gzip_level_config[opt].chain_shift;
good_match = gzip_level_config[opt].good; good_match = gzip_level_config[opt].good;
max_lazy_match = gzip_level_config[opt].lazy2 * 2; max_lazy_match = gzip_level_config[opt].lazy2 * 2;