1/* $NetBSD: strlen.S,v 1.5 2020/09/09 14:49:27 jakllsch 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 34RCSID("$NetBSD: strlen.S,v 1.5 2020/09/09 14:49:27 jakllsch 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 47ENTRY(FUNCNAME) 48 mov x4, x0 /* need x0 for return */ 49 add x9, x0, #8 /* start + dword */ 50 bic x9, x9, #7 /* and aligned */ 51#ifdef STRNLEN 52 adds x10, x0, x1 /* x10 = s + maxlen */ 53 b.cc 1f /* if go past, */ 54 mvn x10, xzr /* set limit 0xffffffffffffffff */ 551: 56#endif 57 mov x11, #MASK8_0x01 /* test mask */ 58 59 ands x3, x4, #7 /* extract alignment */ 60 neg x0, x3 /* alignment fixup */ 61 b.eq .Lstrlen_dword_loop /* already dword aligned */ 62 63 /* 64 * Load the dword containing the leading bytes. Make sure bytes 65 * before the data won't match as NUL. 66 */ 67 add x4, x4, x0 /* make dword aligned */ 68 ldr x7, [x4], #8 /* load dword */ 69#ifdef __AARCH64EB__ 70 rev x7, x7 /* convert to LE */ 71#endif 72 lsl x3, x3, #3 /* convert bytes to bits */ 73 lsl x5, x11, x3 /* make mask for LE */ 74 eor x5, x5, x11 /* invert mask */ 75 orr x7, x7, x5 /* prevent NULs */ 76 b .Lstrlen_dword_loop_noload 77 78.Lstrlen_dword_loop: 79#ifdef STRNLEN 80 cmp x4, x10 81 b.hs .Lstrlen_done 82#endif 83 ldr x7, [x4], #8 /* load dword */ 84#ifdef __AARCH64EB__ 85 rev x7, x7 /* convert to LE */ 86#endif 87.Lstrlen_dword_loop_noload: 88 /* 89 * Use the formula (X - 1) & ~(X | 0x7f) to find NUL bytes. 90 * Any NUL byte found will be replaced by 0x80 otherwise any byte 91 * will be replaced by 0x00. 92 */ 93 sub x6, x7, x11 /* a = X - 1 */ 94 orr x7, x7, #MASK8_0x7f /* b = X | 0x7f */ 95 bic x6, x6, x7 /* a & ~b */ 96 cbz x6, .Lstrlen_dword_loop /* no NULs so get next dword */ 97 98 /* 99 * We know there is a NUL in this dword. Use clz to find it. 100 */ 101 rev x6, x6 /* convert to BE */ 102 clz x6, x6 /* find null byte */ 103 add x0, x0, x6, lsr #3 /* add offset to the length */ 104 105 add x0, x0, x4 /* add end to the length */ 106 sub x0, x0, x9 /* subtract start from the length */ 107#ifdef STRNLEN 108 cmp x0, x1 /* did we go too far? */ 109 csel x0, x0, x1, lo /* yes, return max length */ 110#endif 111 ret 112#ifdef STRNLEN 113.Lstrlen_done: 114 mov x0, x1 115 ret 116#endif 117END(FUNCNAME) 118