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chars: probe for a valid UTF-8 starter byte, instead of overstepping 

Instead of always stepping back four bytes and then tentatively
moving forward again (which is wasteful when most codes are just
one or two bytes long), inspect the preceding bytes one by one
and begin the move forward at the first valid starter byte.

This reduces the backwards searching time by close to 40 percent.
master
Benno Schulenberg 2017-05-02 13:05:58 +02:00
parent f162a6a2ab
commit 09cabcad5d
1 changed files with 14 additions and 2 deletions
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16
src/chars.c
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@ -383,8 +383,20 @@ size_t move_mbleft(const char *buf, size_t pos)
* possible point. */
if (pos < 4)
before = 0;
else
before = pos - 4;
else {
const char *ptr = buf + pos;
if ((signed char)*(--ptr) > -65)
before = pos - 1;
else if ((signed char)*(--ptr) > -65)
before = pos - 2;
else if ((signed char)*(--ptr) > -65)
before = pos - 3;
else if ((signed char)*(--ptr) > -65)
before = pos - 4;
else
before = pos - 1;
}
while (before < pos) {
char_len = parse_mbchar(buf + before, NULL, NULL);