104 lines
2.8 KiB
Groff
104 lines
2.8 KiB
Groff
.\" $NetBSD: ffs32.3,v 1.6 2011/04/08 08:47:50 wiz Exp $
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.\"
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.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jukka Ruohonen.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd April 8, 2011
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.Dt FFS32 3
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.Os
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.Sh NAME
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.Nm ffs32 ,
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.Nm ffs64 ,
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.Nm fls32 ,
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.Nm fls64
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.Nd find first or last bit set
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.Sh SYNOPSIS
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.In sys/bitops.h
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.Ft int
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.Fn ffs32 "uint32_t n"
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.Ft int
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.Fn ffs64 "uint64_t n"
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.Ft int
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.Fn fls32 "uint32_t n"
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.Ft int
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.Fn fls64 "uint64_t n"
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.Sh DESCRIPTION
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The
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.Fn ffs32
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and
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.Fn ffs64
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functions find the first bit set in
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.Fa n
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and return the index of that bit.
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Conversely,
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the
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.Fn fls32
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and
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.Fn fls64
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functions find the last bit set in
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.Fa n ,
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returning the index of the bit.
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.Pp
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The search always starts from the bit 1 (the least significant bit).
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If the argument
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.Fa n
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is zero, each function returns zero.
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.Sh IMPLEMENTATION NOTES
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The described functions are implemented as
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.Em static inline
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functions in the
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.In sys/bitops.h
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header.
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The standard C library includes a more portable
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.Xr ffs 3
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for user applications.
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.\"
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.\" XXX: It is noted in the CVS history of <sys/bitops.h> that MD-optimized
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.\" <machine/bitops.h> is a TODO. If those start to appear, note it here.
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.\"
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.Sh EXAMPLES
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In the following example
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.Va f = 3
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and
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.Va l = 7 :
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.Bd -literal -offset indent
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uint32_t n = 0x44; /* 01000100 */
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int f, l;
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f = ffs32(n);
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l = fls32(n);
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.Ed
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.Sh SEE ALSO
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.Xr bitops 3 ,
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.Xr bits 3 ,
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.Xr bitstring 3 ,
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.Xr ffs 3 ,
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.Xr setbit 9
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.Sh HISTORY
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These functions first appeared in
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.Nx 5.0 .
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