diff options
| author | Daniel Edgecumbe <git@esotericnonsense.com> | 2019-09-02 22:09:15 +0100 |
|---|---|---|
| committer | Denys Vlasenko <vda.linux@googlemail.com> | 2019-09-05 13:26:58 +0200 |
| commit | c660cc1b7714fffbac95c9378ff4b73de650a6de (patch) | |
| tree | e05f4421fc7f0e5c6b9bf39e1e45fbdaedc80769 /archival | |
| parent | ca5d86d52c979cef05a614fb725870c10be9b265 (diff) | |
gzip: set default compression level to 6 when CONFIG_FEATURE_GZIP_LEVELS=n
With this change, GNU gzip -n and BusyBox gzip now produce identical output
assuming that CONFIG_GZIP_FAST=2.
>> Excuse me, but I wonder one thing: Why should we follow
>> strictly with gzip on the no-options default behavior?
> First, the default 6 compression level is a de-facto standard. BSD gzip
> and Apple gzip (on macOS) use this default as well. So there is a
> reasonable expectation that different gzip implementations act the same.
> For instance, if the default for busybox gzip becomes 9, then someone
> writing a script using busybox gzip could reasonably expect that the
> compression level will still be 9 when the same script is run on another
> system. That would be wrong. Implementations should not deviate from
> de-facto standards without a strong reason.
>
> Second, the inherent reason for this default has not gone away. While
> processor speeds have exploded since the default was set, so has the
> typical size of compressed files. Multiple gigabytes are nothing unusual
> these days. And gzip is often used for compression on the fly, precisely
> because it offers a good compromise between speed and compression ratio.
> So I believe 6 continues to be a reasonable default.
function old new delta
deflate 939 927 -12
Signed-off-by: Daniel Edgecumbe <git@esotericnonsense.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'archival')
| -rw-r--r-- | archival/gzip.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/archival/gzip.c b/archival/gzip.c index a543d8c36..b08e60efd 100644 --- a/archival/gzip.c +++ b/archival/gzip.c @@ -52,7 +52,7 @@ aa: 85.1% -- replaced with aa.gz //config: help //config: Enable support for compression levels 4-9. The default level //config: is 6. If levels 1-3 are specified, 4 is used. -//config: If this option is not selected, -N options are ignored and -9 +//config: If this option is not selected, -N options are ignored and -6 //config: is used. //config: //config:config FEATURE_GZIP_DECOMPRESS @@ -259,13 +259,13 @@ enum { #if !ENABLE_FEATURE_GZIP_LEVELS - comp_level = 9, - max_chain_length = 4096, + comp_level = 6, + max_chain_length = 128, /* 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 = 258, + max_lazy_match = 16, /* 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 +277,7 @@ enum { * max_insert_length is used only for compression levels <= 3. */ - good_match = 32, + good_match = 8, /* 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 @@ -286,7 +286,7 @@ enum { * found for specific files. */ - nice_match = 258, /* Stop searching when current match exceeds this */ + nice_match = 128, /* 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. |