405b8029a6
Change-Id: I2864dea04b3faf2d919165dcaa600af5b16c41c8 Signed-off-by: Chris Dearman <chris@mips.com> Signed-off-by: Raghu Gandham <raghu@mips.com>
92 lines
3.2 KiB
ArmAsm
92 lines
3.2 KiB
ArmAsm
/* $NetBSD: ffs.S,v 1.5 2003/04/05 23:08:52 bjh21 Exp $ */
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/*
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* Copyright (c) 2001 Christopher Gilbert
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* All rights reserved.
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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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* 3. The name of the company nor the name of the author may be used to
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* endorse or promote products derived from this software without specific
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* prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* ffs - find first set bit, this algorithm isolates the first set
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* bit, then multiplies the number by 0x0450fbaf which leaves the top
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* 6 bits as an index into the table. This algorithm should be a win
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* over the checking each bit in turn as per the C compiled version.
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*
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* This is the ffs algorithm devised by d.seal and posted to comp.sys.arm on
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* 16 Feb 1994.
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*/
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.text
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.ent ffs
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.type ffs, @function
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.global ffs
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.align 4
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.set noreorder
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ffs:
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#if (__mips==32)
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subu $t0,$0,$a0
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and $a0,$t0
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clz $t0,$a0
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li $v0,32
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j $ra
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subu $v0,$t0
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#else
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/* Size of the ffs routine in bytes
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* This is used to index .L_ffs_table from $t9
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* FIXME: there must be a better way to do this
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*/
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#define FFSSIZE 12*4
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subu $t0,$0,$a0
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and $a0,$t0
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/*
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* now a0 has at most one set bit, call this X
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* if X = 0, all further instructions are skipped
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*/
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sll $t0,$a0,4 /* t0 = X * 0x00000010 */
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or $a0,$t0 /* a0 = X * 0x00000011 */
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sll $t0,$a0,6 /* t0 = X * 0x00000440 */
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or $a0,$t0 /* a0 = X * 0x00000451 */
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sll $t0,$a0,16 /* t0 = X * 0x04510000 */
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subu $a0,$t0,$a0 /* a0 = X * 0x0450fbaf */
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/* now lookup in table indexed on top 6 bits of a0 */
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srl $a0,25
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addu $t9,$a0
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j $ra
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lbu $v0,FFSSIZE($t9)
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.L_ffs_table:
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/* 0 1 2 3 4 5 6 7 */
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.byte 0, 1, 2, 13, 3, 7, 0, 14 /* 0- 7 */
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.byte 4, 0, 8, 0, 0, 0, 0, 15 /* 8-15 */
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.byte 11, 5, 0, 0, 9, 0, 0, 26 /* 16-23 */
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.byte 0, 0, 0, 0, 0, 22, 28, 16 /* 24-31 */
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.byte 32, 12, 6, 0, 0, 0, 0, 0 /* 32-39 */
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.byte 10, 0, 0, 25, 0, 0, 21, 27 /* 40-47 */
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.byte 31, 0, 0, 0, 0, 24, 0, 20 /* 48-55 */
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.byte 30, 0, 23, 19, 29, 18, 17, 0 /* 56-63 */
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#endif
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.end ffs
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