ffs.S revision 1.3
1 /* $NetBSD: ffs.S,v 1.3 2013/09/12 15:36:14 joerg Exp $ */ 2 3 /* 4 * Copyright (c) 1992, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This software was developed by the Computer Systems Engineering group 8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 9 * contributed to Berkeley. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. Neither the name of the University nor the names of its contributors 20 * may be used to endorse or promote products derived from this software 21 * without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 * 35 * from: Header: ffs.s,v 1.3 92/07/07 00:23:57 torek Exp 36 */ 37 38 #include <machine/asm.h> 39 #if defined(LIBC_SCCS) && !defined(lint) 40 #if 0 41 .asciz "@(#)ffs.s 8.1 (Berkeley) 6/4/93" 42 #else 43 RCSID("$NetBSD: ffs.S,v 1.3 2013/09/12 15:36:14 joerg Exp $") 44 #endif 45 #endif /* LIBC_SCCS and not lint */ 46 47 #if 0 48 /* 49 * We have a popcount instruction -- use it. 50 * only uses %o0, %o1, %o2 51 * 52 * Here's the pseudo-code from the v9 spec: 53 * 54 * int ffs(unsigned zz) { 55 * return popc( zz ^ ( ~ (-zz))); 56 * } 57 * 58 * XXXX sptifires and blackbirds don't implement popc, 59 * so we won't use this nice clean code 8^(. 60 */ 61 ENTRY(ffs) 62 neg %o0, %o1 ! %o1 = -zz 63 xnor %o0, %o1, %o2 ! %o2 = zz ^ ~ -zz 64 popc %o2, %o1 65 movrz %o0, %g0, %o1 ! result of ffs(0) should be zero 66 retl 67 mov %o1, %o0 68 #endif 69 /* 70 * ffs returns the number of the rightmost bit set in its argument, 71 * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. 72 * If no bits are set, ffs returns 0. 73 * 74 * We use a table lookup on each byte. 75 * 76 * In each section below, %o1 is the current byte (0, 1, 2, or 3). 77 * The last byte is handled specially: for the first three, 78 * if that byte is nonzero, we return the table value 79 * (plus 0, 8, or 16 for the byte number), but for the last 80 * one, we just return the table value plus 24. This means 81 * that ffstab[0] must be -24 so that ffs(0) will return 0. 82 */ 83 ENTRY(ffs) 84 #ifdef __PIC__ 85 PICCY_SET(ffstab, %o2, %o3) 86 #else 87 set ffstab, %o2 88 #endif 89 andcc %o0, 0xff, %o1 ! get low byte 90 be,a 1f ! try again if 0 91 srl %o0, 8, %o0 ! delay slot, get ready for next byte 92 93 retl ! return ffstab[%o1] 94 ldsb [%o2 + %o1], %o0 95 96 1: 97 andcc %o0, 0xff, %o1 ! byte 1 like byte 0... 98 be,a 2f 99 srl %o0, 8, %o0 ! (use delay to prepare for byte 2) 100 101 ldsb [%o2 + %o1], %o0 102 retl ! return ffstab[%o1] + 8 103 add %o0, 8, %o0 104 105 2: 106 andcc %o0, 0xff, %o1 107 be,a 3f 108 srl %o0, 8, %o0 ! (prepare for byte 3) 109 110 ldsb [%o2 + %o1], %o0 111 retl ! return ffstab[%o1] + 16 112 add %o0, 16, %o0 113 114 3: ! just return ffstab[%o0] + 24 115 ldsb [%o2 + %o0], %o0 116 retl 117 add %o0, 24, %o0 118 119 ffstab: 120 .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ 121 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ 122 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ 123 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ 124 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ 125 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ 126 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ 127 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ 128 .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ 129 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ 130 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ 131 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ 132 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ 133 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ 134 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ 135 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */ 136
Indexes created Wed Sep 24 05:09:52 GMT 2025