ffs.S revision 1.1
1/* $NetBSD: ffs.S,v 1.2 1998/11/26 19:32:10 eeh 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. All advertising materials mentioning features or use of this software 20 * must display the following acknowledgement: 21 * This product includes software developed by the University of 22 * California, Berkeley and its contributors. 23 * 4. Neither the name of the University nor the names of its contributors 24 * may be used to endorse or promote products derived from this software 25 * without specific prior written permission. 26 * 27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 30 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 37 * SUCH DAMAGE. 38 * 39 * Header: ffs.s,v 1.3 92/07/07 00:23:57 torek Exp 40 */ 41 42#if defined(LIBC_SCCS) && !defined(lint) 43#ifdef notdef 44 .asciz "@(#)ffs.s 8.1 (Berkeley) 6/4/93" 45#endif 46 .asciz "$NetBSD: ffs.S,v 1.2 1998/11/26 19:32:10 eeh Exp $" 47#endif /* LIBC_SCCS and not lint */ 48 49#include "DEFS.h" 50 51/* 52 * ffs returns the number of the rightmost bit set in its argument, 53 * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. 54 * If no bits are set, ffs returns 0. 55 * 56 * We use a table lookup on each byte. 57 * 58 * In each section below, %o1 is the current byte (0, 1, 2, or 3). 59 * The last byte is handled specially: for the first three, 60 * if that byte is nonzero, we return the table value 61 * (plus 0, 8, or 16 for the byte number), but for the last 62 * one, we just return the table value plus 24. This means 63 * that ffstab[0] must be -24 so that ffs(0) will return 0. 64 */ 65ENTRY(ffs) 66#ifdef PIC 67 PICCY_SET(_C_LABEL(__ffstab), %o2, %o5) 68#else 69 set _C_LABEL(__ffstab), %o2 70#endif 71 andcc %o0, 0xff, %o1 ! get low byte 72 be,a 1f ! try again if 0 73 srl %o0, 8, %o0 ! delay slot, get ready for next byte 74 75 retl ! return ffstab[%o1] 76 ldsb [%o2 + %o1], %o0 77 781: 79 andcc %o0, 0xff, %o1 ! byte 1 like byte 0... 80 be,a 2f 81 srl %o0, 8, %o0 ! (use delay to prepare for byte 2) 82 83 ldsb [%o2 + %o1], %o0 84 retl ! return ffstab[%o1] + 8 85 add %o0, 8, %o0 86 872: 88 andcc %o0, 0xff, %o1 89 be,a 3f 90 srl %o0, 8, %o0 ! (prepare for byte 3) 91 92 ldsb [%o2 + %o1], %o0 93 retl ! return ffstab[%o1] + 16 94 add %o0, 16, %o0 95 963: ! just return ffstab[%o0] + 24 97 ldsb [%o2 + %o0], %o0 98 retl 99 add %o0, 24, %o0 100 101 .globl _C_LABEL(__ffstab) 102_C_LABEL(__ffstab): 103 .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ 104 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ 105 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ 106 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ 107 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ 108 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ 109 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ 110 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ 111 .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ 112 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ 113 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ 114 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ 115 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ 116 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ 117 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ 118 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */ 119