141 lines
4.9 KiB
ArmAsm
141 lines
4.9 KiB
ArmAsm
/* $NetBSD: ffs.S,v 1.3 1999/12/30 15:30:26 eeh 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. All advertising materials mentioning features or use of this software
|
|
* must display the following acknowledgement:
|
|
* This product includes software developed by the University of
|
|
* California, Berkeley and its contributors.
|
|
* 4. 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.
|
|
*
|
|
* from: Header: ffs.s,v 1.3 92/07/07 00:23:57 torek Exp
|
|
*/
|
|
|
|
#include <machine/asm.h>
|
|
#if defined(LIBC_SCCS) && !defined(lint)
|
|
#if 0
|
|
.asciz "@(#)ffs.s 8.1 (Berkeley) 6/4/93"
|
|
#else
|
|
RCSID("$NetBSD: ffs.S,v 1.3 1999/12/30 15:30:26 eeh Exp $")
|
|
#endif
|
|
#endif /* LIBC_SCCS and not lint */
|
|
|
|
#if 0
|
|
/*
|
|
* We have a popcount instruction -- use it.
|
|
* only uses %o0, %o1, %o2
|
|
*
|
|
* Here's the pseudo-code from the v9 spec:
|
|
*
|
|
* int ffs(unsigned zz) {
|
|
* return popc( zz ^ ( ~ (-zz)));
|
|
* }
|
|
*
|
|
* XXXX sptifires and blackbirds don't implement popc,
|
|
* so we won't use this nice clean code 8^(.
|
|
*/
|
|
ENTRY(ffs)
|
|
neg %o0, %o1 ! %o1 = -zz
|
|
xnor %o0, %o1, %o2 ! %o2 = zz ^ ~ -zz
|
|
popc %o2, %o1
|
|
movrz %o0, %g0, %o1 ! result of ffs(0) should be zero
|
|
retl
|
|
mov %o1, %o0
|
|
#endif
|
|
/*
|
|
* 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(_C_LABEL(ffs))
|
|
#ifdef PIC
|
|
PIC_PROLOGUE(%o1,%o2)
|
|
ld [%o1 + _C_LABEL(__ffstab)], %o2
|
|
#else
|
|
set _C_LABEL(__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
|
|
|
|
ENTRY(_C_LABEL(__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 */
|