Nguyễn Thái Ngọc Duy <[email protected]> writes:
> -O2 build on linux-2.6, without the patch:
Before the result, can you briefly explain what '"*.c" optimization
from exclude' the title talks about is?
When a pattern contains only a single asterisk, e.g. "foo*bar",
after literally comparing the leading part "foo" with the
string, we can compare the tail of the string and make sure it
matches "bar", instead of running fnmatch() on "*bar" against
the remainder of the string.
The funny thing was that trying to explain what the logic should do
makes one realize potential issues in the implementation of that
logic ;-) See below.
> $ time git rev-list --quiet HEAD -- '*.c'
>
> real 0m40.770s
> user 0m40.290s
> sys 0m0.256s
>
> With the patch
>
> $ time ~/w/git/git rev-list --quiet HEAD -- '*.c'
>
> real 0m34.288s
> user 0m33.997s
> sys 0m0.205s
>
> The above command is not supposed to be widely popular.
Hrm, perhaps. I use "git grep <pattern> -- \*.c" quite a lot, but
haven't seen use case for \*.c in the context of the "log" family.
> diff --git a/cache.h b/cache.h
> index bf031f1..d18f584 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -473,6 +473,8 @@ extern int index_name_is_other(const struct index_state
> *, const char *, int);
> extern int ie_match_stat(const struct index_state *, struct cache_entry *,
> struct stat *, unsigned int);
> extern int ie_modified(const struct index_state *, struct cache_entry *,
> struct stat *, unsigned int);
>
> +#define PSF_ONESTAR 1
Together with the GF_ prefix in the previous, PSF_ prefix needs a
bit of in-code explanation. Is it just an RC3L (random combination
of 3 letters?)
> @@ -46,6 +46,12 @@ inline int git_fnmatch(const char *pattern, const char
> *string,
> pattern += prefix;
> string += prefix;
> }
> + if (flags & GF_ONESTAR) {
> + int pattern_len = strlen(++pattern);
> + int string_len = strlen(string);
> + return strcmp(pattern,
> + string + string_len - pattern_len);
> + }
What happens when pattern="foo*oob" and string="foob"?
The prefix match before this code determines that the literal prefix
in the pattern matches with the early part of the string, and makes
pattern="*oob" and string="b".
When you come to strcmp(), you see that string_len is 1, pattern_len
is 3, and pattern is "oob". string+string_len-pattern_len = "oob",
one past the beginning of the original string "foob". They match.
Oops?
return (string_len < pattern_len) ||
strcmp(pattern, string + string_len - pattern_len);
perhaps?
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