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diff: tweak mbstate_t performance

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* lib/mbcel.h (mbcel_scan): Improve performance when initializing
an mbstate_t.
This commit is contained in:
Paul Eggert 2023-07-11 00:50:57 -07:00
parent d28395ef8d
commit 5d0554f0a1
1 changed files with 18 additions and 1 deletions
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19
lib/mbcel.h
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@ -100,8 +100,25 @@ mbcel_scan (char const *p, char const *lim)
if (0 <= *p && *p <= 0x7f)
return (mbcel_t) { .ch = *p, .len = 1 };
char32_t ch;
/* An initial mbstate_t; initialization optimized for some platforms. */
#if defined __GLIBC__ && 2 < __GLIBC__ + (2 <= __GLIBC_MINOR__)
mbstate_t mbs; mbs.__count = 0;
#elif (defined __FreeBSD__ || defined __DragonFly__ || defined __OpenBSD__ \
|| (defined __APPLE__ && defined __MACH__))
/* Initialize for all encodings: UTF-8, EUC, etc. */
union { mbstate_t m; struct { uchar_t ch; int utf8_want, euc_want; } s; } u;
u.s.ch = u.s.utf8_want = u.s.euc_want = 0;
# define mbs u.m
#elif defined __NetBSD__
union { mbstate_t m; struct _RuneLocale *s; } u;
u.s = nullptr;
# define mbs u.m
#else
/* mbstate_t has unknown structure or is not worth optimizing. */
mbstate_t mbs = {0};
#endif
char32_t ch;
size_t len = mbrtoc32 (&ch, p, lim - p, &mbs);
/* Any LEN with top bit set is an encoding error, as LEN == (size_t) -3