1/* 2 * Copyright (C) 2013 ARM Ltd. 3 * Copyright (C) 2013 Linaro. 4 * 5 * This code is based on glibc cortex strings work originally authored by Linaro 6 * and re-licensed under GPLv2 for the Linux kernel. The original code can 7 * be found @ 8 * 9 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/ 10 * files/head:/src/aarch64/ 11 * 12 * This program is free software; you can redistribute it and/or modify 13 * it under the terms of the GNU General Public License version 2 as 14 * published by the Free Software Foundation. 15 * 16 * This program is distributed in the hope that it will be useful, 17 * but WITHOUT ANY WARRANTY; without even the implied warranty of 18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 19 * GNU General Public License for more details. 20 * 21 * You should have received a copy of the GNU General Public License 22 * along with this program. If not, see <http://www.gnu.org/licenses/>. 23 */ 24 25#include <linux/linkage.h> 26#include <asm/assembler.h> 27 28/* 29 * calculate the length of a string 30 * 31 * Parameters: 32 * x0 - const string pointer 33 * Returns: 34 * x0 - the return length of specific string 35 */ 36 37/* Arguments and results. */ 38srcin .req x0 39len .req x0 40 41/* Locals and temporaries. */ 42src .req x1 43data1 .req x2 44data2 .req x3 45data2a .req x4 46has_nul1 .req x5 47has_nul2 .req x6 48tmp1 .req x7 49tmp2 .req x8 50tmp3 .req x9 51tmp4 .req x10 52zeroones .req x11 53pos .req x12 54 55#define REP8_01 0x0101010101010101 56#define REP8_7f 0x7f7f7f7f7f7f7f7f 57#define REP8_80 0x8080808080808080 58 59ENTRY(strlen) 60 mov zeroones, #REP8_01 61 bic src, srcin, #15 62 ands tmp1, srcin, #15 63 b.ne .Lmisaligned 64 /* 65 * NUL detection works on the principle that (X - 1) & (~X) & 0x80 66 * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and 67 * can be done in parallel across the entire word. 68 */ 69 /* 70 * The inner loop deals with two Dwords at a time. This has a 71 * slightly higher start-up cost, but we should win quite quickly, 72 * especially on cores with a high number of issue slots per 73 * cycle, as we get much better parallelism out of the operations. 74 */ 75.Lloop: 76 ldp data1, data2, [src], #16 77.Lrealigned: 78 sub tmp1, data1, zeroones 79 orr tmp2, data1, #REP8_7f 80 sub tmp3, data2, zeroones 81 orr tmp4, data2, #REP8_7f 82 bic has_nul1, tmp1, tmp2 83 bics has_nul2, tmp3, tmp4 84 ccmp has_nul1, #0, #0, eq /* NZCV = 0000 */ 85 b.eq .Lloop 86 87 sub len, src, srcin 88 cbz has_nul1, .Lnul_in_data2 89CPU_BE( mov data2, data1 ) /*prepare data to re-calculate the syndrome*/ 90 sub len, len, #8 91 mov has_nul2, has_nul1 92.Lnul_in_data2: 93 /* 94 * For big-endian, carry propagation (if the final byte in the 95 * string is 0x01) means we cannot use has_nul directly. The 96 * easiest way to get the correct byte is to byte-swap the data 97 * and calculate the syndrome a second time. 98 */ 99CPU_BE( rev data2, data2 ) 100CPU_BE( sub tmp1, data2, zeroones ) 101CPU_BE( orr tmp2, data2, #REP8_7f ) 102CPU_BE( bic has_nul2, tmp1, tmp2 ) 103 104 sub len, len, #8 105 rev has_nul2, has_nul2 106 clz pos, has_nul2 107 add len, len, pos, lsr #3 /* Bits to bytes. */ 108 ret 109 110.Lmisaligned: 111 cmp tmp1, #8 112 neg tmp1, tmp1 113 ldp data1, data2, [src], #16 114 lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ 115 mov tmp2, #~0 116 /* Big-endian. Early bytes are at MSB. */ 117CPU_BE( lsl tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */ 118 /* Little-endian. Early bytes are at LSB. */ 119CPU_LE( lsr tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */ 120 121 orr data1, data1, tmp2 122 orr data2a, data2, tmp2 123 csinv data1, data1, xzr, le 124 csel data2, data2, data2a, le 125 b .Lrealigned 126ENDPROC(strlen) 127