.\"	$NetBSD: ffs32.3,v 1.6 2011/04/08 08:47:50 wiz Exp $
.\"
.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jukka Ruohonen.
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.\" modification, are permitted provided that the following conditions
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.Dd April 8, 2011
.Dt FFS32 3
.Os
.Sh NAME
.Nm ffs32 ,
.Nm ffs64 ,
.Nm fls32 ,
.Nm fls64
.Nd find first or last bit set
.Sh SYNOPSIS
.In sys/bitops.h
.Ft int
.Fn ffs32 "uint32_t n"
.Ft int
.Fn ffs64 "uint64_t n"
.Ft int
.Fn fls32 "uint32_t n"
.Ft int
.Fn fls64 "uint64_t n"
.Sh DESCRIPTION
The
.Fn ffs32
and
.Fn ffs64
functions find the first bit set in
.Fa n
and return the index of that bit.
Conversely,
the
.Fn fls32
and
.Fn fls64
functions find the last bit set in
.Fa n ,
returning the index of the bit.
.Pp
The search always starts from the bit 1 (the least significant bit).
If the argument
.Fa n
is zero, each function returns zero.
.Sh IMPLEMENTATION NOTES
The described functions are implemented as
.Em static inline
functions in the
.In sys/bitops.h
header.
The standard C library includes a more portable
.Xr ffs 3
for user applications.
.\"
.\" XXX: It is noted in the CVS history of <sys/bitops.h> that MD-optimized
.\"	 <machine/bitops.h> is a TODO. If those start to appear, note it here.
.\"
.Sh EXAMPLES
In the following example
.Va f = 3
and
.Va l = 7 :
.Bd -literal -offset indent
uint32_t n = 0x44;	/* 01000100 */
int f, l;

f = ffs32(n);
l = fls32(n);
.Ed
.Sh SEE ALSO
.Xr bitops 3 ,
.Xr bits 3 ,
.Xr bitstring 3 ,
.Xr ffs 3 ,
.Xr setbit 9
.Sh HISTORY
These functions first appeared in
.Nx 5.0 .