1 /* 2 * __strlen_aarch64_sve - compute the length of a string 3 * 4 * Copyright (c) 2018-2021, Arm Limited. 5 * SPDX-License-Identifier: MIT 6 */ 7 8 #include "../asmdefs.h" 9 10 #if __ARM_FEATURE_SVE 11 /* Assumptions: 12 * 13 * ARMv8-a, AArch64 14 * SVE Available. 15 */ 16 17 ENTRY (__strlen_aarch64_sve) 18 PTR_ARG (0) 19 setffr /* initialize FFR */ 20 ptrue p2.b /* all ones; loop invariant */ 21 mov x1, 0 /* initialize length */ 22 23 /* Read a vector's worth of bytes, stopping on first fault. */ 24 .p2align 4 25 0: ldff1b z0.b, p2/z, [x0, x1] 26 rdffrs p0.b, p2/z 27 b.nlast 2f 28 29 /* First fault did not fail: the whole vector is valid. 30 Avoid depending on the contents of FFR beyond the branch. */ 31 incb x1, all /* speculate increment */ 32 cmpeq p1.b, p2/z, z0.b, 0 /* loop if no zeros */ 33 b.none 0b 34 decb x1, all /* undo speculate */ 35 36 /* Zero found. Select the bytes before the first and count them. */ 37 1: brkb p0.b, p2/z, p1.b 38 incp x1, p0.b 39 mov x0, x1 40 ret 41 42 /* First fault failed: only some of the vector is valid. 43 Perform the comparison only on the valid bytes. */ 44 2: cmpeq p1.b, p0/z, z0.b, 0 45 b.any 1b 46 47 /* No zero found. Re-init FFR, increment, and loop. */ 48 setffr 49 incp x1, p0.b 50 b 0b 51 52 END (__strlen_aarch64_sve) 53 54 #endif 55 56