1/* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:49 christos Exp $ */ 2 3/* 4 * Copyright (c) 1995 Christopher G. Demetriou 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. All advertising materials mentioning features or use of this software 16 * must display the following acknowledgement: 17 * This product includes software developed for the 18 * NetBSD Project. See http://www.NetBSD.org/ for 19 * information about NetBSD. 20 * 4. The name of the author may not be used to endorse or promote products 21 * derived from this software without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 24 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 25 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 26 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 27 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 28 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 29 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 30 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 31 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 32 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 33 * 34 * <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>> 35 */ 36 37#include <machine/asm.h> 38 39LEAF(ffs, 1) 40 addl a0, 0, t0 41 beq t0, Lallzero 42 43 /* 44 * Initialize return value (v0), and set up t1 so that it 45 * contains the mask with only the lowest bit set. 46 */ 47 subl zero, t0, t1 48 ldil v0, 1 49 and t0, t1, t1 50 51 and t1, 0xff, t2 52 bne t2, Ldo8 53 54 /* 55 * If lower 16 bits empty, add 16 to result and use upper 16. 56 */ 57 zapnot t1, 0x03, t3 58 bne t3, Ldo16 59 sra t1, 16, t1 60 addl v0, 16, v0 61 62Ldo16: 63 /* 64 * If lower 8 bits empty, add 8 to result and use upper 8. 65 */ 66 and t1, 0xff, t4 67 bne t4, Ldo8 68 sra t1, 8, t1 69 addl v0, 8, v0 70 71Ldo8: 72 and t1, 0x0f, t5 /* lower 4 of 8 empty? */ 73 and t1, 0x33, t6 /* lower 2 of each 4 empty? */ 74 and t1, 0x55, t7 /* lower 1 of each 2 empty? */ 75 76 /* If lower 4 bits empty, add 4 to result. */ 77 bne t5, Ldo4 78 addl v0, 4, v0 79 80Ldo4: /* If lower 2 bits of each 4 empty, add 2 to result. */ 81 bne t6, Ldo2 82 addl v0, 2, v0 83 84Ldo2: /* If lower bit of each 2 empty, add 1 to result. */ 85 bne t7, Ldone 86 addl v0, 1, v0 87 88Ldone: 89 RET 90 91Lallzero: 92 bis zero, zero, v0 93 RET 94END(ffs) 95