найти первый бит в слове (find first bit set in a word)
Имя (Name)
ffs, ffsl, ffsll - find first bit set in a word
Синопсис (Synopsis)
#include <strings.h>
int ffs(int i);
#include <string.h>
int ffsl(long i);
int ffsll(long long i);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
ffs():
Since glibc 2.12:
_XOPEN_SOURCE >= 700
|| ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Before glibc 2.12:
none
ffsl(), ffsll():
Since glibc 2.27:
_DEFAULT_SOURCE
Before glibc 2.27:
_GNU_SOURCE
Описание (Description)
The ffs() function returns the position of the first (least
significant) bit set in the word i. The least significant bit is
position 1 and the most significant position is, for example, 32
or 64. The functions ffsll() and ffsl() do the same but take
arguments of possibly different size.
Возвращаемое значение (Return value)
These functions return the position of the first bit set, or 0 if
no bits are set in i.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ffs(), ffsl(), ffsll() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
ffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.
The ffsl() and ffsll() functions are glibc extensions.
Примечание (Note)
BSD systems have a prototype in <string.h>.
Смотри также (See also)
memchr(3)
