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ffs.S revision 1.4 
      1 /*	$NetBSD: ffs.S,v 1.4 2011/07/04 11:35:26 mrg Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2010 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Matt Thomas of 3am Software Foundry.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <mips/asm.h>
     33 
     34 RCSID("$NetBSD: ffs.S,v 1.4 2011/07/04 11:35:26 mrg Exp $")
     35 
     36 /* bit = ffs(value) */
     37 
     38 	.text
     39 	.set	noreorder
     40 
     41 WEAK_ALIAS(__ffssi2,ffs)
     42 #if __mips == 64 || __mips == 32
     43 LEAF(ffs)
     44 #ifndef _LP64
     45 XLEAF(ffsl)
     46 #endif
     47 	.set	push
     48 	.set	mips32
     49 	li	v1, 32
     50 #if __mips == 64
     51 	sll	a0, a0, 0
     52 #endif
     53 	negu	a1, a0
     54 	and	a0, a1
     55 	clz	v0, a0
     56 	j	ra
     57 	 subu	v0, v1, v0
     58 	.set	pop
     59 END(ffs)
     60 #if defined(_LP64) && __mips == 64
     61 LEAF(ffsl)
     62 	li	v1, 64
     63 	negu	a1, a0
     64 	and	a0, a1
     65 	dclz	v0, a0
     66 	j	ra
     67 	 subu	v0, v1, v0
     68 END(ffsl)
     69 #endif
     70 #else /* __mips != 64 && __mips != 32 */
     71 
     72 #ifdef _LP64
     73 XLEAF(ffsl)
     74 	beqz	a0, 6f			# fast escape if 0
     75 	 li	v0, 0
     76 
     77 	li	v0, 1
     78 	li	a3, 0xffffffff		# initial mask
     79 	b	1f
     80 	 li	a2, 32			# bit count of mask
     81 #endif /* _LP64 */
     82 LEAF(ffs)
     83 #ifndef _LP64
     84 XLEAF(ffsl)
     85 #endif /* !_LP64 */
     86 	beqz	a0, 6f
     87 	 li	v0, 0
     88 
     89 	li	v0, 1
     90 	li	a3, 0xffff		# initial mask
     91 	li	a2, 16			# bit count of mask
     92 1:
     93 	and	v1, a0, a3		# focus no lower half of bits left
     94 	bnez	v1, 2f			# any of the lower half set?
     95 	 nop
     96 	addu	v0, a2			# nope, then bit is in the upper half
     97 #ifdef _LP64
     98 	dsrlv	a0, a0, a2		# discard low bits
     99 #else
    100 	srlv	a0, a0, a2		# discard low bits
    101 #endif
    102 2:
    103 	srl	a2, 1			# divide bit count by 2
    104 	bnez	a2, 1b			# still bits left to text?
    105 	 srlv	a3, a3, a2		# shrink mask in half
    106 6:
    107 	j	ra
    108 	 nop
    109 END(ffs)
    110 #endif /* __mips == 64 || __mips == 32 */
    111