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/*
* __strlen_aarch64_sve - compute the length of a string
*
* Copyright (c) 2018-2021, Arm Limited.
* SPDX-License-Identifier: MIT
*/
#include "../asmdefs.h"
#if __ARM_FEATURE_SVE
/* Assumptions:
*
* ARMv8-a, AArch64
* SVE Available.
*/
ENTRY (__strlen_aarch64_sve)
PTR_ARG (0)
setffr /* initialize FFR */
ptrue p2.b /* all ones; loop invariant */
mov x1, 0 /* initialize length */
/* Read a vector's worth of bytes, stopping on first fault. */
.p2align 4
0: ldff1b z0.b, p2/z, [x0, x1]
rdffrs p0.b, p2/z
b.nlast 2f
/* First fault did not fail: the whole vector is valid.
Avoid depending on the contents of FFR beyond the branch. */
incb x1, all /* speculate increment */
cmpeq p1.b, p2/z, z0.b, 0 /* loop if no zeros */
b.none 0b
decb x1, all /* undo speculate */
/* Zero found. Select the bytes before the first and count them. */
1: brkb p0.b, p2/z, p1.b
incp x1, p0.b
mov x0, x1
ret
/* First fault failed: only some of the vector is valid.
Perform the comparison only on the valid bytes. */
2: cmpeq p1.b, p0/z, z0.b, 0
b.any 1b
/* No zero found. Re-init FFR, increment, and loop. */
setffr
incp x1, p0.b
b 0b
END (__strlen_aarch64_sve)
#endif
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