strlen.S revision 1.1.4.2
1 /* $NetBSD: strlen.S,v 1.1.4.2 2014/08/19 23:45:12 tls Exp $ */ 2 3 /*- 4 * Copyright (c) 2014 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Matt Thomas of 3am Software Foundry. 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 RCSID("$NetBSD: strlen.S,v 1.1.4.2 2014/08/19 23:45:12 tls Exp $") 35 36 #ifdef STRNLEN 37 #define FUNCNAME strnlen 38 /* LINTSTUB: size_t strnlen(const char *, size_t); */ 39 #else 40 #define FUNCNAME strlen 41 /* LINTSTUB: size_t strlen(const char *); */ 42 #endif 43 44 #define MASK8_0x01 0x0101010101010101 45 #define MASK8_0x7f 0x7f7f7f7f7f7f7f7f 46 47 ENTRY(FUNCNAME) 48 mov x4, x0 /* need x0 for return */ 49 add x9, x0, #8 /* start + dword */ 50 #ifdef STRNLEN 51 add x10, x0, x1 /* don't go past here */ 52 #endif 53 mov x11, #MASK8_0x01 /* test mask */ 54 55 ands x3, x4, #7 /* extract alignment */ 56 neg x0, x3 /* alignment fixup */ 57 b.eq .Lstrlen_dword_loop /* already dword aligned */ 58 59 /* 60 * Load the dword containing the leading bytes. Make sure bytes 61 * before the data won't match as NUL. 62 */ 63 add x4, x4, x0 /* make dword aligned */ 64 ldr x7, [x4], #8 /* load dword */ 65 lsl x3, x3, #3 /* convert bytes to bits */ 66 #ifdef __AARCH64EB__ 67 lsr x5, x11, x3 /* make mask for BE */ 68 #else 69 lsl x5, x11, x3 /* make mask for LE */ 70 #endif 71 eor x5, x5, x11 /* invert mask */ 72 orr x7, x7, x5 /* prevent NULs */ 73 b .Lstrlen_dword_loop_noload 74 75 .Lstrlen_dword_loop: 76 #ifdef STRNLEN 77 cmp x4, x10 78 b.ge .Lstrlen_done 79 #endif 80 ldr x7, [x4], #8 /* load dword */ 81 .Lstrlen_dword_loop_noload: 82 /* 83 * Use the formula (X - 1) & ~(X | 0x7f) to find NUL bytes. 84 * Any NUL byte found will be replaced by 0x80 otherwise any byte 85 * will be replaced by 0x00. 86 */ 87 sub x6, x7, x11 /* a = X - 1 */ 88 orr x7, x7, #MASK8_0x7f /* b = X | 0x7f */ 89 bic x6, x6, x7 /* a & ~b */ 90 cbz x6, .Lstrlen_dword_loop /* no NULs so get next dword */ 91 92 /* 93 * We know there is a NUL in this dword. Use clz to find it. 94 */ 95 #ifdef __AARCH64EL__ 96 rev x7, x7 /* convert to BE */ 97 #endif 98 clz x7, x7 /* find null byte */ 99 add x0, x0, x7, lsr #3 /* add offset to the length */ 100 101 add x0, x0, x4 /* add end to the length */ 102 sub x0, x0, x9 /* subtract start from the length */ 103 #ifdef STRNLEN 104 cmp x0, x1 /* did we go too far? */ 105 csel x0, x0, x1, lt /* yes, return max length */ 106 #endif 107 ret 108 #ifdef STRNLEN 109 .Lstrlen_done: 110 mov x0, x1 111 ret 112 #endif 113 END(FUNCNAME) 114
Indexes created Tue Oct 07 21:09:53 GMT 2025