1/* 2 * strnlen - calculate the length of a string with limit. 3 * 4 * Copyright (c) 2020-2022, Arm Limited. 5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception 6 */ 7 8/* Assumptions: 9 * 10 * ARMv8-a, AArch64, Advanced SIMD. 11 * MTE compatible. 12 */ 13 14#include "asmdefs.h" 15 16#define srcin x0 17#define cntin x1 18#define result x0 19 20#define src x2 21#define synd x3 22#define shift x4 23#define tmp x4 24#define cntrem x5 25 26#define qdata q0 27#define vdata v0 28#define vhas_chr v1 29#define vend v2 30#define dend d2 31 32/* 33 Core algorithm: 34 Process the string in 16-byte aligned chunks. Compute a 64-bit mask with 35 four bits per byte using the shrn instruction. A count trailing zeros then 36 identifies the first zero byte. */ 37 38ENTRY (__strnlen_aarch64) 39 PTR_ARG (0) 40 SIZE_ARG (1) 41 bic src, srcin, 15 42 cbz cntin, L(nomatch) 43 ld1 {vdata.16b}, [src] 44 cmeq vhas_chr.16b, vdata.16b, 0 45 lsl shift, srcin, 2 46 shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */ 47 fmov synd, dend 48 lsr synd, synd, shift 49 cbz synd, L(start_loop) 50L(finish): 51 rbit synd, synd 52 clz synd, synd 53 lsr result, synd, 2 54 cmp cntin, result 55 csel result, cntin, result, ls 56 ret 57 58L(nomatch): 59 mov result, cntin 60 ret 61 62L(start_loop): 63 sub tmp, src, srcin 64 add tmp, tmp, 17 65 subs cntrem, cntin, tmp 66 b.lo L(nomatch) 67 68 /* Make sure that it won't overread by a 16-byte chunk */ 69 tbz cntrem, 4, L(loop32_2) 70 sub src, src, 16 71 .p2align 5 72L(loop32): 73 ldr qdata, [src, 32]! 74 cmeq vhas_chr.16b, vdata.16b, 0 75 umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */ 76 fmov synd, dend 77 cbnz synd, L(end) 78L(loop32_2): 79 ldr qdata, [src, 16] 80 subs cntrem, cntrem, 32 81 cmeq vhas_chr.16b, vdata.16b, 0 82 b.lo L(end_2) 83 umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */ 84 fmov synd, dend 85 cbz synd, L(loop32) 86L(end_2): 87 add src, src, 16 88L(end): 89 shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */ 90 sub result, src, srcin 91 fmov synd, dend 92#ifndef __AARCH64EB__ 93 rbit synd, synd 94#endif 95 clz synd, synd 96 add result, result, synd, lsr 2 97 cmp cntin, result 98 csel result, cntin, result, ls 99 ret 100 101END (__strnlen_aarch64) 102 103