diff options
Diffstat (limited to 'string/aarch64/strlen-mte.S')
| -rw-r--r-- | string/aarch64/strlen-mte.S | 41 |
1 files changed, 19 insertions, 22 deletions
diff --git a/string/aarch64/strlen-mte.S b/string/aarch64/strlen-mte.S index 7cf41d5..7723579 100644 --- a/string/aarch64/strlen-mte.S +++ b/string/aarch64/strlen-mte.S @@ -1,8 +1,8 @@ /* * strlen - calculate the length of a string. * - * Copyright (c) 2020, Arm Limited. - * SPDX-License-Identifier: MIT + * Copyright (c) 2020-2022, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception */ /* Assumptions: @@ -11,7 +11,7 @@ * MTE compatible. */ -#include "../asmdefs.h" +#include "asmdefs.h" #define srcin x0 #define result x0 @@ -19,35 +19,26 @@ #define src x1 #define synd x2 #define tmp x3 -#define wtmp w3 #define shift x4 #define data q0 #define vdata v0 #define vhas_nul v1 -#define vrepmask v2 -#define vend v3 -#define dend d3 +#define vend v2 +#define dend d2 /* Core algorithm: - - For each 16-byte chunk we calculate a 64-bit syndrome value with four bits - per byte. For even bytes, bits 0-3 are set if the relevant byte matched the - requested character or the byte is NUL. Bits 4-7 must be zero. Bits 4-7 are - set likewise for odd bytes so that adjacent bytes can be merged. Since the - bits in the syndrome reflect the order in which things occur in the original - string, counting trailing zeros identifies exactly which byte matched. */ + Process the string in 16-byte aligned chunks. Compute a 64-bit mask with + four bits per byte using the shrn instruction. A count trailing zeros then + identifies the first zero byte. */ ENTRY (__strlen_aarch64_mte) PTR_ARG (0) bic src, srcin, 15 - mov wtmp, 0xf00f ld1 {vdata.16b}, [src] - dup vrepmask.8h, wtmp cmeq vhas_nul.16b, vdata.16b, 0 lsl shift, srcin, 2 - and vhas_nul.16b, vhas_nul.16b, vrepmask.16b - addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */ + shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */ fmov synd, dend lsr synd, synd, shift cbz synd, L(loop) @@ -59,19 +50,25 @@ ENTRY (__strlen_aarch64_mte) .p2align 5 L(loop): - ldr data, [src, 16]! + ldr data, [src, 16] + cmeq vhas_nul.16b, vdata.16b, 0 + umaxp vend.16b, vhas_nul.16b, vhas_nul.16b + fmov synd, dend + cbnz synd, L(loop_end) + ldr data, [src, 32]! cmeq vhas_nul.16b, vdata.16b, 0 umaxp vend.16b, vhas_nul.16b, vhas_nul.16b fmov synd, dend cbz synd, L(loop) - - and vhas_nul.16b, vhas_nul.16b, vrepmask.16b - addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */ + sub src, src, 16 +L(loop_end): + shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */ sub result, src, srcin fmov synd, dend #ifndef __AARCH64EB__ rbit synd, synd #endif + add result, result, 16 clz tmp, synd add result, result, tmp, lsr 2 ret |