154401Storek/* 2*61174Sbostic * Copyright (c) 1992, 1993 3*61174Sbostic * The Regents of the University of California. All rights reserved. 454401Storek * 554401Storek * This software was developed by the Computer Systems Engineering group 654401Storek * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 754401Storek * contributed to Berkeley. 854401Storek * 954401Storek * %sccs.include.redist.c% 1054401Storek * 1154729Storek * from: $Header: ffs.s,v 1.3 92/07/07 00:23:57 torek Exp $ 1254401Storek */ 1354401Storek 1454401Storek#if defined(LIBC_SCCS) && !defined(lint) 15*61174Sbostic .asciz "@(#)ffs.s 8.1 (Berkeley) 06/04/93" 1654401Storek#endif /* LIBC_SCCS and not lint */ 1754401Storek 1854729Storek#include "DEFS.h" 1954729Storek 2054401Storek/* 2154401Storek * ffs returns the number of the rightmost bit set in its argument, 2254401Storek * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero. 2354401Storek * If no bits are set, ffs returns 0. 2454401Storek * 2554401Storek * We use a table lookup on each byte. 2654401Storek * 2754401Storek * In each section below, %o1 is the current byte (0, 1, 2, or 3). 2854401Storek * The last byte is handled specially: for the first three, 2954401Storek * if that byte is nonzero, we return the table value 3054401Storek * (plus 0, 8, or 16 for the byte number), but for the last 3154401Storek * one, we just return the table value plus 24. This means 3254401Storek * that ffstab[0] must be -24 so that ffs(0) will return 0. 3354401Storek */ 3454729StorekENTRY(ffs) 3554401Storek set ffstab, %o2 3654401Storek andcc %o0, 0xff, %o1 ! get low byte 3754401Storek be,a 1f ! try again if 0 3854729Storek srl %o0, 8, %o0 ! delay slot, get ready for next byte 3954401Storek 4054401Storek retl ! return ffstab[%o1] 4154729Storek ldsb [%o2 + %o1], %o0 4254401Storek 4354401Storek1: 4454401Storek andcc %o0, 0xff, %o1 ! byte 1 like byte 0... 4554401Storek be,a 2f 4654729Storek srl %o0, 8, %o0 ! (use delay to prepare for byte 2) 4754401Storek 4854401Storek ldsb [%o2 + %o1], %o0 4954401Storek retl ! return ffstab[%o1] + 8 5054729Storek add %o0, 8, %o0 5154401Storek 5254401Storek2: 5354401Storek andcc %o0, 0xff, %o1 5454401Storek be,a 3f 5554729Storek srl %o0, 8, %o0 ! (prepare for byte 3) 5654401Storek 5754401Storek ldsb [%o2 + %o1], %o0 5854401Storek retl ! return ffstab[%o1] + 16 5954729Storek add %o0, 16, %o0 6054401Storek 6154401Storek3: ! just return ffstab[%o0] + 24 6254401Storek ldsb [%o2 + %o0], %o0 6354401Storek retl 6454729Storek add %o0, 24, %o0 6554729Storek 6654729Storekffstab: 6754729Storek .byte -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */ 6854729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-1f */ 6954729Storek .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 20-2f */ 7054729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 30-3f */ 7154729Storek .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 40-4f */ 7254729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 50-5f */ 7354729Storek .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 60-6f */ 7454729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 70-7f */ 7554729Storek .byte 8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 80-8f */ 7654729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 10-9f */ 7754729Storek .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* a0-af */ 7854729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* b0-bf */ 7954729Storek .byte 7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* c0-cf */ 8054729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* d0-df */ 8154729Storek .byte 6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* e0-ef */ 8254729Storek .byte 5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* f0-ff */ 83