strlen.S revision 1.1
1 /* $NetBSD: strlen.S,v 1.1 2005/12/20 19:28:50 christos Exp $ */ 2 3 /* 4 * Copyright 2002 Wasabi Systems, Inc. 5 * All rights reserved. 6 * 7 * Written by Eduardo Horvath for Wasabi Systems, Inc. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. All advertising materials mentioning features or use of this software 18 * must display the following acknowledgement: 19 * This product includes software developed for the NetBSD Project by 20 * Wasabi Systems, Inc. 21 * 4. The name of Wasabi Systems, Inc. may not be used to endorse 22 * or promote products derived from this software without specific prior 23 * written permission. 24 * 25 * THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND 26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL WASABI SYSTEMS, INC 29 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35 * POSSIBILITY OF SUCH DAMAGE. 36 */ 37 38 39 40 #include <machine/asm.h> 41 #if defined(LIBC_SCCS) && !defined(lint) 42 RCSID("$NetBSD: strlen.S,v 1.1 2005/12/20 19:28:50 christos Exp $") 43 #endif /* LIBC_SCCS and not lint */ 44 45 /* The algorithm here uses the following techniques: 46 * 47 * 1) Given a word 'x', we can test to see if it contains any 0 bytes 48 * by subtracting 0x01010101, and seeing if any of the high bits of each 49 * byte changed from 0 to 1. This works because the least significant 50 * 0 byte must have had no incoming carry (otherwise it's not the least 51 * significant), so it is 0x00 - 0x01 == 0xff. For all other 52 * byte values, either they have the high bit set initially, or when 53 * 1 is subtracted you get a value in the range 0x00-0x7f, none of which 54 * have their high bit set. The expression here is 55 * (x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when 56 * there were no 0x00 bytes in the word. 57 * 58 * 2) Now just hunt for the first byte that's 0x00 in 'x'. 59 * 60 * This is from the book 'The PowerPC Compiler Writer's Guide', 61 * by Steve Hoxey, Faraydon Karim, Bill Hay and Hank Warren. 62 */ 63 64 ENTRY(strlen) 65 /* 66 * Calculate address for and load the first xword. 67 */ 68 andn %o0, 0x7, %o1 69 ldx [%o1], %g1 70 71 /* 72 * Now prepare some constants while the data arrives... 73 */ 74 sethi %hi(0xfefefefe), %o3 75 sethi %hi(0x7f7f7f7f), %o2 76 77 or %o3, %lo(0xfefefefe), %o3 78 or %o2, %lo(0x7f7f7f7f), %o2 79 80 sllx %o3, 32, %o5 81 andcc %o0, 0x7, %g5 ! Hoisted from below to fill a slot 82 83 sllx %o2, 32, %o4 84 or %o3, %o5, %o3 85 86 sll %g5, 3, %g5 ! Convert to bytes. hoisted 87 or %o2, %o4, %o2 88 89 inc %o3 90 neg %g5 ! hoisted 91 92 /* 93 * Mask off the leading bits: 94 * 95 * if (ptr & 0x7) 96 * mask = -1 << (64 - ((ptr & 0x7) << 3)); 97 */ 98 99 ! andcc %o0, 0x7, %g5 ! Hoisted above 100 bz,pt %icc, 0f 101 102 103 ! sll %g5, 3, %g5 ! Convert to bytes. Also hoisted 104 105 ! neg %g5 ! Hoisted 106 107 add %g5, 64, %g5 108 mov -1, %o4 109 110 sllx %o4, %g5, %o4 111 112 or %o4, %g1, %g1 ! Make leading bytes != 0 113 114 0: 115 or %g1, %o2, %o5 ! Do step 1 -- use or/andn instead of nor/and 116 add %g1, %o3, %g5 117 118 inc 8, %o1 ! Point to next word 119 andncc %g5, %o5, %g0 120 bz,a,pt %xcc, 0b 121 ldx [%o1], %g1 122 123 mov -1, %o4 124 dec 8, %o1 125 126 sllx %o4, 64-8, %o5 127 128 btst %g1, %o5 ! Check high byte 129 bz %xcc,0f 130 srlx %o5, 8, %o5 131 132 inc %o1 133 btst %g1, %o5 ! Check 2nd byte 134 bz %xcc,0f 135 srlx %o5, 8, %o5 136 137 inc %o1 138 btst %g1, %o5 ! Check 3rd byte 139 bz %xcc,0f 140 srlx %o5, 8, %o5 141 142 inc %o1 143 btst %g1, %o5 ! Check 4th byte 144 bz %xcc,0f 145 srlx %o5, 8, %o5 146 147 inc %o1 148 btst %g1, %o5 ! Check 5th byte 149 bz %xcc,0f 150 srlx %o5, 8, %o5 151 152 inc %o1 153 btst %g1, %o5 ! Check 6th byte 154 bz %xcc,0f 155 srlx %o5, 8, %o5 156 157 inc %o1 158 btst %g1, %o5 ! Check 7th byte 159 bz %xcc,0f 160 nop 161 162 inc %o1 163 0: 164 retl 165 sub %o1, %o0, %o0 ! return length (ptr - (origptr+1)) 166
Indexes created Tue Sep 23 02:09:52 GMT 2025