I was profiling 'git-rev-list v2.16.12..', because I suspected
insert_by_date() might be expensive (the function inserts into
singly-linked ordered list, so the data structure has to become
array based to allow optimization). But profiling showed it was
not the bottleneck. Probably because the kernel history is not
that bushy and we do not have too many "active" heads during
traversal.
But I noticed something else.
Flat profile:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
21.52 0.17 0.17 2800320 0.00 0.00 hexval
15.19 0.29 0.12 70008 0.00 0.00 get_sha1_hex
15.19 0.41 0.12 70008 0.00 0.00 lookup_object
15.19 0.53 0.12 68495 0.00 0.00 find_pack_entry_one
11.39 0.62 0.09 198667 0.00 0.00 insert_obj_hash
7.60 0.68 0.06 34675 0.00 0.00 unpack_object_header_gently
3.80 0.71 0.03 33819 0.00 0.02 parse_commit_buffer
1.27 0.72 0.01 103822 0.00 0.00 commit_list_insert
1.27 0.73 0.01 67640 0.00 0.00 prepare_packed_git
1.27 0.74 0.01 67611 0.00 0.00 created_object
1.27 0.75 0.01 33820 0.00 0.00 use_packed_git
1.27 0.76 0.01 33819 0.00 0.00 lookup_tree
1.27 0.77 0.01 1 10.00 10.00 prepare_packed_git_one
1.27 0.78 0.01 parse_tree_indirect
1.27 0.79 0.01 verify_filename
...
The attached brings get_sha1_hex() down from 15.19% to 5.41%,
but I feel we should be able to do better.
Is this barking up the wrong tree? Or did I pick a good target
but the shooter wasn't skilled enough?
diff --git a/sha1_file.c b/sha1_file.c
index 428d791..00aa364 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -26,26 +26,30 @@ const unsigned char null_sha1[20];
static unsigned int sha1_file_open_flag = O_NOATIME;
-static unsigned hexval(char c)
-{
- if (c >= '0' && c <= '9')
- return c - '0';
- if (c >= 'a' && c <= 'f')
- return c - 'a' + 10;
- if (c >= 'A' && c <= 'F')
- return c - 'A' + 10;
- return ~0;
-}
+static const unsigned char hexval[] = {
+ 0, 1, 2, 3, 4, 5, 6, 7, /* 30-37 */
+ 8, 9, 255, 255, 255, 255, 255, 255, /* 38-3F */
+ 255, 10, 11, 12, 13, 14, 15, 255, /* 40-47 */
+ 255, 255, 255, 255, 255, 255, 255, 255, /* 48-4F */
+ 255, 255, 255, 255, 255, 255, 255, 255, /* 50-57 */
+ 255, 255, 255, 255, 255, 255, 255, 255, /* 58-5F */
+ 255, 10, 11, 12, 13, 14, 15, 255, /* 60-67 */
+};
int get_sha1_hex(const char *hex, unsigned char *sha1)
{
int i;
for (i = 0; i < 20; i++) {
- unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
- if (val & ~0xff)
+ unsigned int v, w, val;
+ v = *hex++;
+ if ((v < '0') || ('f' < v) ||
+ ((v = hexval[v-'0']) == 255))
+ return -1;
+ w = *hex++;
+ if ((w < '0') || ('f' < w) ||
+ ((w = hexval[w-'0']) == 255))
return -1;
- *sha1++ = val;
- hex += 2;
+ *sha1++ = (v << 4) | w;
}
return 0;
}
-
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