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/* $OpenBSD: ffs.S,v 1.5 2012/08/22 17:19:35 pascal Exp $ */
/*
* Copyright (c) 1992, 1993
* The Regents of the University of California. All rights reserved.
*
* This software was developed by the Computer Systems Engineering group
* at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
* contributed to Berkeley.
*
* Redistribution and use in source and binary forms, with or without
* 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.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "DEFS.h"
/*
* ffs returns the number of the rightmost bit set in its argument,
* i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero.
* If no bits are set, ffs returns 0.
*
* We use a table lookup on each byte.
*
* In each section below, %o1 is the current byte (0, 1, 2, or 3).
* The last byte is handled specially: for the first three,
* if that byte is nonzero, we return the table value
* (plus 0, 8, or 16 for the byte number), but for the last
* one, we just return the table value plus 24. This means
* that ffstab[0] must be -24 so that ffs(0) will return 0.
*/
ENTRY(ffs)
#ifdef __PIC__
PICCY_SET(ffstab, %o2, %o5)
#else
set ffstab, %o2
#endif
andcc %o0, 0xff, %o1 ! get low byte
be,a 1f ! try again if 0
srl %o0, 8, %o0 ! delay slot, get ready for next byte
retl ! return ffstab[%o1]
ldsb [%o2 + %o1], %o0
1:
andcc %o0, 0xff, %o1 ! byte 1 like byte 0...
be,a 2f
srl %o0, 8, %o0 ! (use delay to prepare for byte 2)
ldsb [%o2 + %o1], %o0
retl ! return ffstab[%o1] + 8
add %o0, 8, %o0
2:
andcc %o0, 0xff, %o1
be,a 3f
srl %o0, 8, %o0 ! (prepare for byte 3)
ldsb [%o2 + %o1], %o0
retl ! return ffstab[%o1] + 16
add %o0, 16, %o0
3: ! just return ffstab[%o0] + 24
ldsb [%o2 + %o0], %o0
retl
add %o0, 24, %o0
ffstab:
.byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */
.byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */
.byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */
.byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */
.byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */
.byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */
.byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */
.byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */
.byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */
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