\" $NetBSD: ffs32.3,v 1.6 2011/04/08 08:47:50 wiz Exp $
\"
\" Copyright (c) 2010 The NetBSD Foundation, Inc.
\" All rights reserved.
\"
\" 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
\" are met:
\" 1. Redistributions of source code must retain the above copyright
\" notice, this list of conditions and the following disclaimer.
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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 .
