1 /* $OpenBSD: ffs.S,v 1.6 2022年12月08日 01:25:46 guenther Exp $ */ 2 /* $NetBSD: ffs.S,v 1.2 1998年11月26日 19:32:10 eeh Exp $ */ 3 4 /* 5 * Copyright (c) 1992, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * This software was developed by the Computer Systems Engineering group 9 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 10 * contributed to Berkeley. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * Header: ffs.s,v 1.3 92/07/07 00:23:57 torek Exp 37 */ 38 39#include "DEFS.h" 40 41 /* 42 * ffs returns the number of the rightmost bit set in its argument, 43 * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. 44 * If no bits are set, ffs returns 0. 45 * 46 * We use a table lookup on each byte. 47 * 48 * In each section below, %o1 is the current byte (0, 1, 2, or 3). 49 * The last byte is handled specially: for the first three, 50 * if that byte is nonzero, we return the table value 51 * (plus 0, 8, or 16 for the byte number), but for the last 52 * one, we just return the table value plus 24. This means 53 * that ffstab[0] must be -24 so that ffs(0) will return 0. 54 */ 55 ENTRY(ffs) 56#ifdef PIC 57 PICCY_SET(__ffstab, %o2, %o5) 58#else 59 set __ffstab, %o2 60#endif 61 andcc %o0, 0xff, %o1 ! get low byte 62 be,a 1f ! try again if 0 63 srl %o0, 8, %o0 ! delay slot, get ready for next byte 64 65 retl ! return ffstab[%o1] 66 ldsb [%o2 + %o1], %o0 67 68 1: 69 andcc %o0, 0xff, %o1 ! byte 1 like byte 0... 70 be,a 2f 71 srl %o0, 8, %o0 ! (use delay to prepare for byte 2) 72 73 ldsb [%o2 + %o1], %o0 74 retl ! return ffstab[%o1] + 8 75 add %o0, 8, %o0 76 77 2: 78 andcc %o0, 0xff, %o1 79 be,a 3f 80 srl %o0, 8, %o0 ! (prepare for byte 3) 81 82 ldsb [%o2 + %o1], %o0 83 retl ! return ffstab[%o1] + 16 84 add %o0, 16, %o0 85 86 3: ! just return ffstab[%o0] + 24 87 ldsb [%o2 + %o0], %o0 88 retl 89 add %o0, 24, %o0 90 END(ffs) 91 92 .globl __ffstab 93 __ffstab: 94 .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ 95 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ 96 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ 97 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ 98 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ 99 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ 100 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ 101 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ 102 .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ 103 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ 104 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ 105 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ 106 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ 107 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ 108 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ 109 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */ 110