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* Copyright (C) 2013 ARM Ltd.
* Copyright (C) 2013 Linaro.
* This code is based on glibc cortex strings work originally authored by Linaro
* and re-licensed under GPLv2 for the Linux kernel. The original code can
* be found @
* files/head:/src/aarch64/
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <>.
#include <linux/linkage.h>
#include <asm/assembler.h>
* determine the length of a fixed-size string
* Parameters:
* x0 - const string pointer
* x1 - maximal string length
* Returns:
* x0 - the return length of specific string
/* Arguments and results. */
srcin .req x0
len .req x0
limit .req x1
/* Locals and temporaries. */
src .req x2
data1 .req x3
data2 .req x4
data2a .req x5
has_nul1 .req x6
has_nul2 .req x7
tmp1 .req x8
tmp2 .req x9
tmp3 .req x10
tmp4 .req x11
zeroones .req x12
pos .req x13
limit_wd .req x14
#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080
cbz limit, .Lhit_limit
mov zeroones, #REP8_01
bic src, srcin, #15
ands tmp1, srcin, #15 .Lmisaligned
/* Calculate the number of full and partial words -1. */
sub limit_wd, limit, #1 /* Limit != 0, so no underflow. */
lsr limit_wd, limit_wd, #4 /* Convert to Qwords. */
* 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.
ldp data1, data2, [src], #16
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
sub tmp3, data2, zeroones
orr tmp4, data2, #REP8_7f
bic has_nul1, tmp1, tmp2
bic has_nul2, tmp3, tmp4
subs limit_wd, limit_wd, #1
orr tmp1, has_nul1, has_nul2
ccmp tmp1, #0, #0, pl /* NZCV = 0000 */
b.eq .Lloop
cbz tmp1, .Lhit_limit /* No null in final Qword. */
* We know there's a null in the final Qword. The easiest thing
* to do now is work out the length of the string and return
* MIN (len, limit).
sub len, src, srcin
cbz has_nul1, .Lnul_in_data2
CPU_BE( mov data2, data1 ) /*perpare data to re-calculate the syndrome*/
sub len, len, #8
mov has_nul2, has_nul1
* 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.
CPU_BE( rev data2, data2 )
CPU_BE( sub tmp1, data2, zeroones )
CPU_BE( orr tmp2, data2, #REP8_7f )
CPU_BE( bic has_nul2, tmp1, tmp2 )
sub len, len, #8
rev has_nul2, has_nul2
clz pos, has_nul2
add len, len, pos, lsr #3 /* Bits to bytes. */
cmp len, limit
csel len, len, limit, ls /* Return the lower value. */
* Deal with a partial first word.
* We're doing two things in parallel here;
* 1) Calculate the number of words (but avoiding overflow if
* limit is near ULONG_MAX) - to do this we need to work out
* limit + tmp1 - 1 as a 65-bit value before shifting it;
* 2) Load and mask the initial data words - we force the bytes
* before the ones we are interested in to 0xff - this ensures
* early bytes will not hit any zero detection.
ldp data1, data2, [src], #16
sub limit_wd, limit, #1
and tmp3, limit_wd, #15
lsr limit_wd, limit_wd, #4
add tmp3, tmp3, tmp1
add limit_wd, limit_wd, tmp3, lsr #4
neg tmp4, tmp1
lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */
mov tmp2, #~0
/* Big-endian. Early bytes are at MSB. */
CPU_BE( lsl tmp2, tmp2, tmp4 ) /* Shift (tmp1 & 63). */
/* Little-endian. Early bytes are at LSB. */
CPU_LE( lsr tmp2, tmp2, tmp4 ) /* Shift (tmp1 & 63). */
cmp tmp1, #8
orr data1, data1, tmp2
orr data2a, data2, tmp2
csinv data1, data1, xzr, le
csel data2, data2, data2a, le
b .Lrealigned
mov len, limit