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AArch64: Implement optimized strlen.

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Marcus Shawcroft 2013-01-16 13:57:42 +00:00
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commit d542f8ed21
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ports/ChangeLog.aarch64
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2013-01-17 Marcus Shawcroft <marcus.shawcroft@linaro.org>
* sysdeps/aarch64/strlen.S: New file.
2013-01-17 Marcus Shawcroft <marcus.shawcroft@linaro.org> 2013-01-17 Marcus Shawcroft <marcus.shawcroft@linaro.org>
* sysdeps/aarch64/strcmp.S: New file. * sysdeps/aarch64/strcmp.S: New file.

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ports/sysdeps/aarch64/strlen.S Normal file
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/* Copyright (C) 2012-2013 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* Assumptions:
*
* ARMv8-a, AArch64
*/
/* Arguments and results. */
#define srcin x0
#define len x0
/* Locals and temporaries. */
#define src x1
#define data1 x2
#define data2 x3
#define data2a x4
#define has_nul1 x5
#define has_nul2 x6
#define tmp1 x7
#define tmp2 x8
#define tmp3 x9
#define tmp4 x10
#define zeroones x11
#define pos x12
#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080
/* Start of critial section -- keep to one 64Byte cache line. */
ENTRY_ALIGN (strlen, 6)
mov zeroones, #REP8_01
bic src, srcin, #15
ands tmp1, srcin, #15
b.ne L(misaligned)
/* NUL detection works on the principle that (X - 1) & (~X) & 0x80
(=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
can be done in parallel across the entire word. */
/* The inner loop deals with two Dwords at a time. This has a
slightly higher start-up cost, but we should win quite quickly,
especially on cores with a high number of issue slots per
cycle, as we get much better parallelism out of the operations. */
L(loop):
ldp data1, data2, [src], #16
L(realigned):
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
sub tmp3, data2, zeroones
orr tmp4, data2, #REP8_7f
bic has_nul1, tmp1, tmp2
bics has_nul2, tmp3, tmp4
ccmp has_nul1, #0, #0, eq /* NZCV = 0000 */
b.eq L(loop)
/* End of critical section -- keep to one 64Byte cache line. */
sub len, src, srcin
cbz has_nul1, L(nul_in_data2)
#ifdef __AARCH64EB__
mov data2, data1
#endif
sub len, len, #8
mov has_nul2, has_nul1
L(nul_in_data2):
#ifdef __AARCH64EB__
/* For big-endian, carry propagation (if the final byte in the
string is 0x01) means we cannot use has_nul directly. The
easiest way to get the correct byte is to byte-swap the data
and calculate the syndrome a second time. */
rev data2, data2
sub tmp1, data2, zeroones
orr tmp2, data2, #REP8_7f
bic has_nul2, tmp1, tmp2
#endif
sub len, len, #8
rev has_nul2, has_nul2
clz pos, has_nul2
add len, len, pos, lsr #3 /* Bits to bytes. */
RET
L(misaligned):
cmp tmp1, #8
neg tmp1, tmp1
ldp data1, data2, [src], #16
lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
mov tmp2, #~0
#ifdef __AARCH64EB__
/* Big-endian. Early bytes are at MSB. */
lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
#else
/* Little-endian. Early bytes are at LSB. */
lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
#endif
orr data1, data1, tmp2
orr data2a, data2, tmp2
csinv data1, data1, xzr, le
csel data2, data2, data2a, le
b L(realigned)
END (strlen)
libc_hidden_builtin_def (strlen)