ffs.S revision 1.2
1/* 2 * Copyright (c) 1992, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This software was developed by the Computer Systems Engineering group 6 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 7 * contributed to Berkeley. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 */ 33 34#include <machine/asm.h> 35/* 36 * ffs returns the number of the rightmost bit set in its argument, 37 * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. 38 * If no bits are set, ffs returns 0. 39 * 40 * We use a table lookup on each byte. 41 * 42 * In each section below, %o1 is the current byte (0, 1, 2, or 3). 43 * The last byte is handled specially: for the first three, 44 * if that byte is nonzero, we return the table value 45 * (plus 0, 8, or 16 for the byte number), but for the last 46 * one, we just return the table value plus 24. This means 47 * that ffstab[0] must be -24 so that ffs(0) will return 0. 48 */ 49ENTRY(ffs) 50#ifdef PIC 51 PICCY_SET(_C_LABEL(__ffstab), %o2, %o3) 52#else 53 set _C_LABEL(__ffstab), %o2 54#endif 55 andcc %o0, 0xff, %o1 ! get low byte 56 be,a 1f ! try again if 0 57 srl %o0, 8, %o0 ! delay slot, get ready for next byte 58 59 retl ! return ffstab[%o1] 60 ldsb [%o2 + %o1], %o0 61 621: 63 andcc %o0, 0xff, %o1 ! byte 1 like byte 0... 64 be,a 2f 65 srl %o0, 8, %o0 ! (use delay to prepare for byte 2) 66 67 ldsb [%o2 + %o1], %o0 68 retl ! return ffstab[%o1] + 8 69 add %o0, 8, %o0 70 712: 72 andcc %o0, 0xff, %o1 73 be,a 3f 74 srl %o0, 8, %o0 ! (prepare for byte 3) 75 76 ldsb [%o2 + %o1], %o0 77 retl ! return ffstab[%o1] + 16 78 add %o0, 16, %o0 79 803: ! just return ffstab[%o0] + 24 81 ldsb [%o2 + %o0], %o0 82 retl 83 add %o0, 24, %o0 84 85_C_LABEL(__ffstab): 86 .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ 87 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ 88 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ 89 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ 90 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ 91 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ 92 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ 93 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ 94 .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ 95 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ 96 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ 97 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ 98 .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ 99 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ 100 .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ 101 .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */ 102