1/* 2 * strrchr - find the last of a character in a string 3 * 4 * Copyright (c) 2019, Arm Limited. 5 * SPDX-License-Identifier: MIT 6 */ 7 8/* Assumptions: 9 * 10 * ARMv8-a, AArch64 11 * SVE Available. 12 */ 13 14 .arch armv8-a+sve 15 .text 16 17 .globl __strrchr_aarch64_sve 18 .type __strrchr_aarch64_sve, %function 19 .p2align 4 20__strrchr_aarch64_sve: 21 dup z1.b, w1 /* replicate byte across vector */ 22 setffr /* initialize FFR */ 23 ptrue p1.b /* all ones; loop invariant */ 24 mov x2, 0 /* no match found so far */ 25 pfalse p2.b 26 27 .p2align 4 28 /* Read a vector's worth of bytes, stopping on first fault. */ 290: ldff1b z0.b, p1/z, [x0, xzr] 30 rdffrs p0.b, p1/z 31 b.nlast 1f 32 33 /* First fault did not fail: the whole vector is valid. 34 Avoid depending on the contents of FFR beyond the branch. */ 35 incb x0, all /* skip bytes this round */ 36 cmpeq p3.b, p1/z, z0.b, 0 /* search for 0 */ 37 b.any 3f 38 39 cmpeq p3.b, p1/z, z0.b, z1.b /* search for c; no eos */ 40 b.none 0b 41 42 mov x2, x0 /* save advanced base */ 43 mov p2.b, p3.b /* save current search */ 44 b 0b 45 46 /* First fault failed: only some of the vector is valid. 47 Perform the comparisions only on the valid bytes. */ 481: cmpeq p3.b, p0/z, z0.b, 0 /* search for 0 */ 49 b.any 2f 50 51 cmpeq p3.b, p0/z, z0.b, z1.b /* search for c; no eos */ 52 mov x3, x0 53 incp x0, p0.b /* skip bytes this round */ 54 setffr /* re-init FFR */ 55 b.none 0b 56 57 addvl x2, x3, 1 /* save advanced base */ 58 mov p2.b, p3.b /* save current search */ 59 b 0b 60 61 /* Found end-of-string. */ 622: incb x0, all /* advance base */ 633: brka p3.b, p1/z, p3.b /* mask after first 0 */ 64 cmpeq p3.b, p3/z, z0.b, z1.b /* search for c not after eos */ 65 b.any 4f 66 67 /* No C within last vector. Did we have one before? */ 68 cbz x2, 5f 69 mov x0, x2 /* restore advanced base */ 70 mov p3.b, p2.b /* restore saved search */ 71 72 /* Find the *last* match in the predicate. This is slightly 73 more complicated than finding the first match. */ 744: rev p3.b, p3.b /* reverse the bits */ 75 brka p3.b, p1/z, p3.b /* find position of last match */ 76 decp x0, p3.b /* retard pointer to last match */ 77 ret 78 79 /* No C whatsoever. Return NULL. */ 805: mov x0, 0 81 ret 82 83 .size __strrchr_aarch64_sve, . - __strrchr_aarch64_sve 84