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