1/* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $ */ 2 3/*- 4 * Copyright (c) 2002 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by ITOH Yasufumi. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32#include <machine/asm.h> 33 34/* 35 * ffs - find first bit set 36 * 37 * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions. 38 * The remaining 8bit is tested in every 2bit. 39 */ 40 41ENTRY(ffs) 42 mov r4,r0 ! using r0 specific instructions 43 tst #0xff,r0 44 bf/s L8bit 45 mov #0+1,r1 ! ret = 1..8 46 47 tst r0,r0 ! ffs(0) is 0 48 bt Lzero ! testing here to accelerate ret=1..8 cases 49 50 shlr8 r0 51 tst #0xff,r0 52 bf/s L8bit 53 mov #8+1,r1 ! ret = 9..16 54 55 shlr8 r0 56 tst #0xff,r0 57 bf/s L8bit 58 mov #16+1,r1 ! ret = 17..24 59 60 shlr8 r0 61 mov #24+1,r1 ! ret = 25..32 62 63L8bit: 64 tst #0x0f,r0 65 bt 4f 66 67 tst #0x03,r0 68 bt 2f 69 tst #0x01,r0 ! not bit 0 -> T 70 mov #0,r0 71 rts 72 addc r1,r0 ! 0 + r1 + T -> r0 73 742: tst #0x04,r0 75 mov #2,r0 76 rts 77 addc r1,r0 78 794: tst #0x30,r0 80 bt 6f 81 tst #0x10,r0 82 mov #4,r0 83 rts 84 addc r1,r0 85 866: tst #0x40,r0 87 mov #6,r0 88 rts 89 addc r1,r0 90 91Lzero: rts 92 nop 93