ffs.S revision 1.1
1 /* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos 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 1.1 2005/12/20 19:28:50 christos Exp $") 44 #endif 45 #endif /* LIBC_SCCS and not lint */ 46 47 /* 48 * ffs returns the number of the rightmost bit set in its argument, 49 * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. 50 * If no bits are set, ffs returns 0. 51 * 52 * We use a table lookup on each byte. 53 * 54 * In each section below, %o1 is the current byte (0, 1, 2, or 3). 55 * The last byte is handled specially: for the first three, 56 * if that byte is nonzero, we return the table value 57 * (plus 0, 8, or 16 for the byte number), but for the last 58 * one, we just return the table value plus 24. This means 59 * that ffstab[0] must be -24 so that ffs(0) will return 0. 60 */ 61 ENTRY(ffs) 62 #ifdef PIC 63 PICCY_SET(_C_LABEL(__ffstab), %o2, %o3) 64 #else 65 set _C_LABEL(__ffstab), %o2 66 #endif 67 andcc %o0, 0xff, %o1 ! get low byte 68 be,a 1f ! try again if 0 69 srl %o0, 8, %o0 ! delay slot, get ready for next byte 70 71 retl ! return ffstab[%o1] 72 ldsb [%o2 + %o1], %o0 73 74 1: 75 andcc %o0, 0xff, %o1 ! byte 1 like byte 0... 76 be,a 2f 77 srl %o0, 8, %o0 ! (use delay to prepare for byte 2) 78 79 ldsb [%o2 + %o1], %o0 80 retl ! return ffstab[%o1] + 8 81 add %o0, 8, %o0 82 83 2: 84 andcc %o0, 0xff, %o1 85 be,a 3f 86 srl %o0, 8, %o0 ! (prepare for byte 3) 87 88 ldsb [%o2 + %o1], %o0 89 retl ! return ffstab[%o1] + 16 90 add %o0, 16, %o0 91 92 3: ! just return ffstab[%o0] + 24 93 ldsb [%o2 + %o0], %o0 94 retl 95 add %o0, 24, %o0 96 97 RODATA(__ffstab) 98 .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ 99 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ 100 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ 101 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ 102 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ 103 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ 104 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ 105 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ 106 .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ 107 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ 108 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ 109 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ 110 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ 111 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ 112 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ 113 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */ 114
Indexes created Tue Sep 23 07:09:52 GMT 2025