/* $OpenBSD: ffs.S,v 1.10 2023/01/13 17:52:08 miod Exp $ */ /* * Copyright (c) 1992, 1993 * The Regents of the University of California. All rights reserved. * * This software was developed by the Computer Systems Engineering group * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and * contributed to Berkeley. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include "SYS.h" /* * ffs returns the number of the rightmost bit set in its argument, * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. * If no bits are set, ffs returns 0. * * We use a table lookup on each byte. * * In each section below, %o1 is the current byte (0, 1, 2, or 3). * The last byte is handled specially: for the first three, * if that byte is nonzero, we return the table value * (plus 0, 8, or 16 for the byte number), but for the last * one, we just return the table value plus 24. This means * that ffstab[0] must be -24 so that ffs(0) will return 0. */ ENTRY(ffs) #ifdef __PIC__ PIC_PROLOGUE(%o5, %o4) set __ffstab, %o4 ldx [%o5 + %o4], %o2 #else set __ffstab, %o2 #endif andcc %o0, 0xff, %o1 ! get low byte be,a 1f ! try again if 0 srl %o0, 8, %o0 ! delay slot, get ready for next byte retl ! return ffstab[%o1] ldsb [%o2 + %o1], %o0 1: andcc %o0, 0xff, %o1 ! byte 1 like byte 0... be,a 2f srl %o0, 8, %o0 ! (use delay to prepare for byte 2) ldsb [%o2 + %o1], %o0 retl ! return ffstab[%o1] + 8 add %o0, 8, %o0 2: andcc %o0, 0xff, %o1 be,a 3f srl %o0, 8, %o0 ! (prepare for byte 3) ldsb [%o2 + %o1], %o0 retl ! return ffstab[%o1] + 16 add %o0, 16, %o0 3: ! just return ffstab[%o0] + 24 ldsb [%o2 + %o0], %o0 retl add %o0, 24, %o0 END(ffs) .protected ffs .section .rodata __ffstab: .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */
