| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
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| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
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| .\" the use of the information contained herein. The author(s) may not |
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| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Modified Sat Jul 24 19:39:35 1993 by Rik Faith (faith@cs.unc.edu) |
| .\" |
| .\" Modified 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de) |
| .\" |
| .TH FFS 3 2021-03-22 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| ffs, ffsl, ffsll \- find first bit set in a word |
| .SH SYNOPSIS |
| .nf |
| .B #include <strings.h> |
| .PP |
| .BI "int ffs(int " i ); |
| .PP |
| .B #include <string.h> |
| .PP |
| .BI "int ffsl(long " i ); |
| .BI "int ffsll(long long " i ); |
| .fi |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR ffs (): |
| .nf |
| 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 |
| .fi |
| .PP |
| .BR ffsl (), |
| .BR ffsll (): |
| .nf |
| Since glibc 2.27: |
| .\" glibc commit 68fe16dd327c895c08b9ee443b234c49c13b36e9 |
| _DEFAULT_SOURCE |
| Before glibc 2.27: |
| _GNU_SOURCE |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR ffs () |
| function returns the position of the first |
| (least significant) bit set in the word \fIi\fP. |
| The least significant bit is position 1 and the |
| most significant position is, for example, 32 or 64. |
| The functions |
| .BR ffsll () |
| and |
| .BR ffsl () |
| do the same but take |
| arguments of possibly different size. |
| .SH RETURN VALUE |
| These functions return the position of the first bit set, |
| or 0 if no bits are set in |
| .IR i . |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR ffs (), |
| .BR ffsl (), |
| .BR ffsll () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| .BR ffs (): |
| POSIX.1-2001, POSIX.1-2008, 4.3BSD. |
| .PP |
| The |
| .BR ffsl () |
| and |
| .BR ffsll () |
| functions are glibc extensions. |
| .SH NOTES |
| BSD systems have a prototype in |
| .IR <string.h> . |
| .SH SEE ALSO |
| .BR memchr (3) |