1/* $NetBSD: ffs.S,v 1.3 2011/01/23 06:47:14 matt 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 34RCSID("$NetBSD: ffs.S,v 1.3 2011/01/23 06:47:14 matt Exp $") 35 36/* bit = ffs(value) */ 37 38 .text 39 .set noreorder 40 41#if __mips == 64 || __mips == 32 42LEAF(ffs) 43#ifndef _LP64 44XLEAF(ffsl) 45#endif 46 .set push 47 .set mips32 48 li v1, 32 49#if __mips == 64 50 sll a0, a0, 0 51#endif 52 negu a1, a0 53 and a0, a1 54 clz v0, a0 55 j ra 56 subu v0, v1, v0 57 .set pop 58END(ffs) 59#if defined(_LP64) && __mips == 64 60LEAF(ffsl) 61 li v1, 64 62 negu a1, a0 63 and a0, a1 64 dclz v0, a0 65 j ra 66 subu v0, v1, v0 67END(ffsl) 68#endif 69#else /* __mips != 64 && __mips != 32 */ 70 71#ifdef _LP64 72XLEAF(ffsl) 73 beqz a0, 6f # fast escape if 0 74 li v0, 0 75 76 li v0, 1 77 li a3, 0xffffffff # initial mask 78 b 1f 79 li a2, 32 # bit count of mask 80#endif /* _LP64 */ 81LEAF(ffs) 82#ifndef _LP64 83XLEAF(ffsl) 84#endif /* !_LP64 */ 85 beqz a0, 6f 86 li v0, 0 87 88 li v0, 1 89 li a3, 0xffff # initial mask 90 li a2, 16 # bit count of mask 911: 92 and v1, a0, a3 # focus no lower half of bits left 93 bnez v1, 2f # any of the lower half set? 94 nop 95 addu v0, a2 # nope, then bit is in the upper half 96#ifdef _LP64 97 dsrlv a0, a0, a2 # discard low bits 98#else 99 srlv a0, a0, a2 # discard low bits 100#endif 1012: 102 srl a2, 1 # divide bit count by 2 103 bnez a2, 1b # still bits left to text? 104 srlv a3, a3, a2 # shrink mask in half 1056: 106 j ra 107 nop 108END(ffs) 109#endif /* __mips == 64 || __mips == 32 */ 110