ffs.S revision 1.1
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 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 #include <machine/asm.h> 40 41 #if defined(LIBC_SCCS) && !defined(lint) 42 RCSID("$NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $") 43 #endif 44 45 /* 46 * ffs - find first bit set 47 * 48 * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions. 49 * The remaining 8bit is tested in every 2bit. 50 */ 51 52 ENTRY(ffs) 53 mov r4,r0 ! using r0 specific instructions 54 tst #0xff,r0 55 bf/s L8bit 56 mov #0+1,r1 ! ret = 1..8 57 58 tst r0,r0 ! ffs(0) is 0 59 bt Lzero ! testing here to accelerate ret=1..8 cases 60 61 shlr8 r0 62 tst #0xff,r0 63 bf/s L8bit 64 mov #8+1,r1 ! ret = 9..16 65 66 shlr8 r0 67 tst #0xff,r0 68 bf/s L8bit 69 mov #16+1,r1 ! ret = 17..24 70 71 shlr8 r0 72 mov #24+1,r1 ! ret = 25..32 73 74 L8bit: 75 tst #0x0f,r0 76 bt 4f 77 78 tst #0x03,r0 79 bt 2f 80 tst #0x01,r0 ! not bit 0 -> T 81 mov #0,r0 82 rts 83 addc r1,r0 ! 0 + r1 + T -> r0 84 85 2: tst #0x04,r0 86 mov #2,r0 87 rts 88 addc r1,r0 89 90 4: tst #0x30,r0 91 bt 6f 92 tst #0x10,r0 93 mov #4,r0 94 rts 95 addc r1,r0 96 97 6: tst #0x40,r0 98 mov #6,r0 99 rts 100 addc r1,r0 101 102 Lzero: rts 103 nop 104
Indexes created Mon Sep 29 21:09:56 GMT 2025