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Avoid hashing same memory location twice by truncating overlapping byte ranges,

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it's speed optimization as the inner code also checks that previous hash value
is not same as new hash value. Essentially those two checks together makes the
compression a little more efficient as it can remember matches further apart.
As far as I remember from my tests, the secondary path was triggered only twice
in very long uncompressed file, but the gain in compression rate was still noticeable.
This commit is contained in:
Mika Lindqvist 2017-02-14 11:40:52 +02:00 committed by Hans Kristian Rosbach
parent bcb013d915
commit 53204685c0
1 changed files with 16 additions and 11 deletions
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15
deflate_medium.c
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@ -68,18 +68,19 @@ static void insert_match(deflate_state *s, struct match match) {
}
}
#else
if (likely(match.match_length == 1)) {
match.strstart++;
match.match_length = 0;
}else{
match.strstart++;
match.match_length--;
if (match.match_length > 0) {
if (match.strstart >= match.orgstart) {
if (match.strstart + match.match_length - 1 >= match.orgstart) {
insert_string(s, match.strstart, match.match_length);
} else {
insert_string(s, match.strstart, match.orgstart - match.strstart + 1);
}
match.strstart += match.match_length;
match.match_length = 0;
}
}
#endif
return;
}
@ -102,7 +103,11 @@ static void insert_match(deflate_state *s, struct match match) {
} while (--match.match_length != 0);
#else
if (likely(match.strstart >= match.orgstart)) {
if (likely(match.strstart + match.match_length - 1 >= match.orgstart)) {
insert_string(s, match.strstart, match.match_length);
} else {
insert_string(s, match.strstart, match.orgstart - match.strstart + 1);
}
}
match.strstart += match.match_length;
match.match_length = 0;
@ -111,7 +116,7 @@ static void insert_match(deflate_state *s, struct match match) {
match.strstart += match.match_length;
match.match_length = 0;
s->ins_h = s->window[match.strstart];
if (match.strstart >= 1)
if (match.strstart >= (MIN_MATCH - 2))
#ifndef NOT_TWEAK_COMPILER
insert_string(s, match.strstart + 2 - MIN_MATCH, MIN_MATCH - 2);
#else