1/* $OpenBSD: ffs.S,v 1.2 2008/06/26 05:42:05 ray Exp $ */ 2/* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $ */ 3 4/*- 5 * Copyright (c) 2002 The NetBSD Foundation, Inc. 6 * All rights reserved. 7 * 8 * This code is derived from software contributed to The NetBSD Foundation 9 * by ITOH Yasufumi. 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 * 20 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 24 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 30 * POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33#include <machine/asm.h> 34 35/* 36 * ffs - find first bit set 37 * 38 * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions. 39 * The remaining 8bit is tested in every 2bit. 40 */ 41 42ENTRY(ffs) 43 mov r4,r0 ! using r0 specific instructions 44 tst #0xff,r0 45 bf/s L8bit 46 mov #0+1,r1 ! ret = 1..8 47 48 tst r0,r0 ! ffs(0) is 0 49 bt Lzero ! testing here to accelerate ret=1..8 cases 50 51 shlr8 r0 52 tst #0xff,r0 53 bf/s L8bit 54 mov #8+1,r1 ! ret = 9..16 55 56 shlr8 r0 57 tst #0xff,r0 58 bf/s L8bit 59 mov #16+1,r1 ! ret = 17..24 60 61 shlr8 r0 62 mov #24+1,r1 ! ret = 25..32 63 64L8bit: 65 tst #0x0f,r0 66 bt 4f 67 68 tst #0x03,r0 69 bt 2f 70 tst #0x01,r0 ! not bit 0 -> T 71 mov #0,r0 72 rts 73 addc r1,r0 ! 0 + r1 + T -> r0 74 752: tst #0x04,r0 76 mov #2,r0 77 rts 78 addc r1,r0 79 804: tst #0x30,r0 81 bt 6f 82 tst #0x10,r0 83 mov #4,r0 84 rts 85 addc r1,r0 86 876: tst #0x40,r0 88 mov #6,r0 89 rts 90 addc r1,r0 91 92Lzero: rts 93 nop 94