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gzip: fix compression level bug. Closes 9131
fix broken logic to get the gzip_level_config value from options -1 to
-9.
This fixes an off-by-one bug that caused gzip -9 output bigger files
than the other compression levels.
It fixes so that compression level 1 to 3 are actually mapped to level 4
as comments say.
It also fixes that levels -4 to -9 is mapped to correct level and avoids
out-of-bounds access.
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
--- a/archival/gzip.c
+++ b/archival/gzip.c
@@ -2220,10 +2220,7 @@ int gzip_main(int argc UNUSED_PARAM, cha
opt >>= ENABLE_GUNZIP ? 7 : 5; /* drop cfv[dt]qn bits */
if (opt == 0)
opt = 1 << 6; /* default: 6 */
- /* Map 1..3 to 4 */
- if (opt & 0x7)
- opt |= 1 << 4;
- opt = ffs(opt >> 3);
+ opt = ffs(opt >> 4); /* Maps -1..-4 to [0], -5 to [1] ... -9 to [5] */
max_chain_length = 1 << gzip_level_config[opt].chain_shift;
good_match = gzip_level_config[opt].good;
max_lazy_match = gzip_level_config[opt].lazy2 * 2;
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