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chars: speed up the parsing of a character for the plain ASCII case 

Again, if the most significant bit of a UTF-8 byte is zero, it means
the character is a single byte and we can skip the call of mblen(),
*and* if the character is one byte it also occupies just one column,
because all ASCII characters are single-column characters -- apart
from control codes.

This partially addresses https://savannah.gnu.org/bugs/?51491.
master
Benno Schulenberg 2018-06-04 13:39:54 +02:00
parent cc2b19c8fd
commit 9a7ba5db79
1 changed files with 12 additions and 7 deletions
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19
src/chars.c
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@ -294,14 +294,17 @@ int parse_mbchar(const char *buf, char *chr, size_t *col)
{
#ifdef ENABLE_UTF8
if (use_utf8) {
/* Get the number of bytes in the multibyte character. */
int length = mblen(buf, MAXCHARLEN);
int length;
/* When the multibyte sequence is invalid, only take the first byte. */
if (length <= 0) {
IGNORE_CALL_RESULT(mblen(NULL, 0));
/* If this is a UTF-8 starter byte, get the number of bytes of the character. */
if ((signed char)*buf < 0) {
length = mblen(buf, MAXCHARLEN);
/* When the multibyte sequence is invalid, only take the first byte. */
if (length <= 0)
length = 1;
} else
length = 1;
}
/* When requested, store the multibyte character in chr. */
if (chr != NULL) {
@ -322,7 +325,9 @@ int parse_mbchar(const char *buf, char *chr, size_t *col)
else if (is_cntrl_mbchar(buf)) {
*col += 2;
/* If we have a normal character, get its width normally. */
} else
} else if (length == 1)
*col += 1;
else
*col += mbwidth(buf);
}