FFS(3P) POSIX Programmer's Manual FFS(3P)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

ffs — find first set bit

#include <strings.h>
int ffs(int i);

The ffs() function shall find the first bit set (beginning with the least significant bit) in i, and return the index of that bit. Bits are numbered starting at one (the least significant bit).

The ffs() function shall return the index of the first bit set. If i is 0, then ffs() shall return 0.

No errors are defined.

The following sections are informative.





The Base Definitions volume of POSIX.1‐2017, <strings.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

2017 IEEE/The Open Group