procyberian/emacs
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Speed up count_size_as_multibyte

Browse source 
This function is used in many places to calculate the length of
a unibyte string converted to multibyte.

* src/character.c (count_size_as_multibyte): Move the overflow test
outside the loop, which makes it much faster.  Standard compilers
will even vectorise it if asked to (-O2 in Clang, -O3 in GCC).
This commit is contained in:
Mattias Engdegård 2022-02-16 12:27:59 +01:00
parent bc84c31823
commit 3b7d55a801
1 changed files with 7 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

15
src/character.c
View file

@ -654,15 +654,14 @@ str_as_multibyte (unsigned char *str, ptrdiff_t len, ptrdiff_t nbytes,
ptrdiff_t
count_size_as_multibyte (const unsigned char *str, ptrdiff_t len)
{
const unsigned char *endp = str + len;
/* Count the number of non-ASCII (raw) bytes, since they will occupy
two bytes in a multibyte string. */
ptrdiff_t nonascii = 0;
for (ptrdiff_t i = 0; i < len; i++)
nonascii += str[i] >> 7;
ptrdiff_t bytes;
for (bytes = 0; str < endp; str++)
{
int n = *str < 0x80 ? 1 : 2;
if (INT_ADD_WRAPV (bytes, n, &bytes))
string_overflow ();
}
if (INT_ADD_WRAPV (len, nonascii, &bytes))
string_overflow ();
return bytes;
}