1 /* 2 * strchr - find a character in a string 3 * 4 * Copyright (c) 2014-2020, Arm Limited. 5 * SPDX-License-Identifier: MIT 6 */ 7 8 /* Assumptions: 9 * 10 * ARMv8-a, AArch64 11 * Neon Available. 12 */ 13 14 #include "../asmdefs.h" 15 16 /* Arguments and results. */ 17 #define srcin x0 18 #define chrin w1 19 20 #define result x0 21 22 #define src x2 23 #define tmp1 x3 24 #define wtmp2 w4 25 #define tmp3 x5 26 27 #define vrepchr v0 28 #define vdata1 v1 29 #define vdata2 v2 30 #define vhas_nul1 v3 31 #define vhas_nul2 v4 32 #define vhas_chr1 v5 33 #define vhas_chr2 v6 34 #define vrepmask_0 v7 35 #define vrepmask_c v16 36 #define vend1 v17 37 #define vend2 v18 38 39 /* Core algorithm. 40 41 For each 32-byte hunk we calculate a 64-bit syndrome value, with 42 two bits per byte (LSB is always in bits 0 and 1, for both big 43 and little-endian systems). For each tuple, bit 0 is set iff 44 the relevant byte matched the requested character; bit 1 is set 45 iff the relevant byte matched the NUL end of string (we trigger 46 off bit0 for the special case of looking for NUL). Since the bits 47 in the syndrome reflect exactly the order in which things occur 48 in the original string a count_trailing_zeros() operation will 49 identify exactly which byte is causing the termination, and why. */ 50 51 /* Locals and temporaries. */ 52 53 ENTRY (__strchr_aarch64) 54 PTR_ARG (0) 55 /* Magic constant 0xc0300c03 to allow us to identify which lane 56 matches the requested byte. Even bits are set if the character 57 matches, odd bits if either the char is NUL or matches. */ 58 mov wtmp2, 0x0c03 59 movk wtmp2, 0xc030, lsl 16 60 dup vrepchr.16b, chrin 61 bic src, srcin, #31 /* Work with aligned 32-byte hunks. */ 62 dup vrepmask_c.4s, wtmp2 63 ands tmp1, srcin, #31 64 add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */ 65 b.eq L(loop) 66 67 /* Input string is not 32-byte aligned. Rather than forcing 68 the padding bytes to a safe value, we calculate the syndrome 69 for all the bytes, but then mask off those bits of the 70 syndrome that are related to the padding. */ 71 ld1 {vdata1.16b, vdata2.16b}, [src], #32 72 neg tmp1, tmp1 73 cmeq vhas_nul1.16b, vdata1.16b, #0 74 cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b 75 cmeq vhas_nul2.16b, vdata2.16b, #0 76 cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b 77 bif vhas_nul1.16b, vhas_chr1.16b, vrepmask_0.16b 78 bif vhas_nul2.16b, vhas_chr2.16b, vrepmask_0.16b 79 and vend1.16b, vhas_nul1.16b, vrepmask_c.16b 80 and vend2.16b, vhas_nul2.16b, vrepmask_c.16b 81 lsl tmp1, tmp1, #1 82 addp vend1.16b, vend1.16b, vend2.16b // 256->128 83 mov tmp3, #~0 84 addp vend1.16b, vend1.16b, vend2.16b // 128->64 85 lsr tmp1, tmp3, tmp1 86 87 mov tmp3, vend1.d[0] 88 bic tmp1, tmp3, tmp1 // Mask padding bits. 89 cbnz tmp1, L(tail) 90 91 .p2align 4 92 L(loop): 93 ld1 {vdata1.16b, vdata2.16b}, [src], #32 94 cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b 95 cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b 96 cmhs vhas_nul1.16b, vhas_chr1.16b, vdata1.16b 97 cmhs vhas_nul2.16b, vhas_chr2.16b, vdata2.16b 98 orr vend1.16b, vhas_nul1.16b, vhas_nul2.16b 99 umaxp vend1.16b, vend1.16b, vend1.16b 100 mov tmp1, vend1.d[0] 101 cbz tmp1, L(loop) 102 103 /* Termination condition found. Now need to establish exactly why 104 we terminated. */ 105 bif vhas_nul1.16b, vhas_chr1.16b, vrepmask_0.16b 106 bif vhas_nul2.16b, vhas_chr2.16b, vrepmask_0.16b 107 and vend1.16b, vhas_nul1.16b, vrepmask_c.16b 108 and vend2.16b, vhas_nul2.16b, vrepmask_c.16b 109 addp vend1.16b, vend1.16b, vend2.16b // 256->128 110 addp vend1.16b, vend1.16b, vend2.16b // 128->64 111 mov tmp1, vend1.d[0] 112 L(tail): 113 /* Count the trailing zeros, by bit reversing... */ 114 rbit tmp1, tmp1 115 /* Re-bias source. */ 116 sub src, src, #32 117 clz tmp1, tmp1 /* And counting the leading zeros. */ 118 /* Tmp1 is even if the target charager was found first. Otherwise 119 we've found the end of string and we weren't looking for NUL. */ 120 tst tmp1, #1 121 add result, src, tmp1, lsr #1 122 csel result, result, xzr, eq 123 ret 124 125 END (__strchr_aarch64) 126 127