ffs.S revision 1.3.44.2
1 /* $NetBSD: ffs.S,v 1.3.44.2 2020/04/21 19:37:46 martin 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 #if defined(LIBC_SCCS) && !defined(lint) 35 RCSID("$NetBSD: ffs.S,v 1.3.44.2 2020/04/21 19:37:46 martin Exp $") 36 #endif 37 38 /* 39 * ffs - find first bit set 40 * 41 * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions. 42 * The remaining 8bit is tested in every 2bit. 43 */ 44 45 WEAK_ALIAS(__ffssi2,ffs) 46 ENTRY(ffs) 47 mov r4,r0 ! using r0 specific instructions 48 tst #0xff,r0 49 bf/s L8bit 50 mov #0+1,r1 ! ret = 1..8 51 52 tst r0,r0 ! ffs(0) is 0 53 bt Lzero ! testing here to accelerate ret=1..8 cases 54 55 shlr8 r0 56 tst #0xff,r0 57 bf/s L8bit 58 mov #8+1,r1 ! ret = 9..16 59 60 shlr8 r0 61 tst #0xff,r0 62 bf/s L8bit 63 mov #16+1,r1 ! ret = 17..24 64 65 shlr8 r0 66 mov #24+1,r1 ! ret = 25..32 67 68 L8bit: 69 tst #0x0f,r0 70 bt 4f 71 72 tst #0x03,r0 73 bt 2f 74 tst #0x01,r0 ! not bit 0 -> T 75 mov #0,r0 76 rts 77 addc r1,r0 ! 0 + r1 + T -> r0 78 79 2: tst #0x04,r0 80 mov #2,r0 81 rts 82 addc r1,r0 83 84 4: tst #0x30,r0 85 bt 6f 86 tst #0x10,r0 87 mov #4,r0 88 rts 89 addc r1,r0 90 91 6: tst #0x40,r0 92 mov #6,r0 93 rts 94 addc r1,r0 95 96 Lzero: rts 97 nop 98
Indexes created Mon Sep 29 03:10:08 GMT 2025