104 lines
3.0 KiB
ArmAsm
104 lines
3.0 KiB
ArmAsm
/* strlen -- find the length of a nul-terminated string.
|
|
Copyright (C) 2013-2014 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>
|
|
|
|
.syntax unified
|
|
.text
|
|
|
|
ENTRY (strlen)
|
|
@ r0 = start of string
|
|
sfi_breg r0, \
|
|
ldrb r2, [\B] @ load the first byte asap
|
|
|
|
@ To cater to long strings, we want to search through a few
|
|
@ characters until we reach an aligned pointer. To cater to
|
|
@ small strings, we don't want to start doing word operations
|
|
@ immediately. The compromise is a maximum of 16 bytes less
|
|
@ whatever is required to end with an aligned pointer.
|
|
@ r3 = number of characters to search in alignment loop
|
|
and r3, r0, #7
|
|
mov r1, r0 @ Save the input pointer
|
|
rsb r3, r3, #15 @ 16 - 1 peeled loop iteration
|
|
cmp r2, #0
|
|
beq 99f
|
|
|
|
@ Loop until we find ...
|
|
1: sfi_breg r0, \
|
|
ldrb r2, [\B, #1]!
|
|
subs r3, r3, #1 @ ... the aligment point
|
|
it ne
|
|
cmpne r2, #0 @ ... or EOS
|
|
bne 1b
|
|
|
|
@ Disambiguate the exit possibilites above
|
|
cmp r2, #0 @ Found EOS
|
|
beq 99f
|
|
add r0, r0, #1
|
|
|
|
@ So now we're aligned.
|
|
sfi_breg r0, \
|
|
ldrd r2, r3, [\B], #8
|
|
#ifdef ARCH_HAS_T2
|
|
movw ip, #0x0101
|
|
sfi_pld r0, #64
|
|
movt ip, #0x0101
|
|
#else
|
|
ldr ip, =0x01010101
|
|
sfi_pld r0, #64
|
|
#endif
|
|
|
|
@ Loop searching for EOS, 8 bytes at a time.
|
|
@ Subtracting (unsigned saturating) from 1 for any byte means that
|
|
@ we get 1 for any byte that was originally zero and 0 otherwise.
|
|
@ Therefore we consider the lsb of each byte the "found" bit.
|
|
.balign 16
|
|
2: uqsub8 r2, ip, r2 @ Find EOS
|
|
uqsub8 r3, ip, r3
|
|
sfi_pld r0, #128 @ Prefetch 2 lines ahead
|
|
orrs r3, r3, r2 @ Combine the two words
|
|
it eq
|
|
sfi_breg r0, \
|
|
ldrdeq r2, r3, [\B], #8
|
|
beq 2b
|
|
|
|
@ Found something. Disambiguate between first and second words.
|
|
@ Adjust r0 to point to the word containing the match.
|
|
@ Adjust r2 to the found bits for the word containing the match.
|
|
cmp r2, #0
|
|
sub r0, r0, #4
|
|
ite eq
|
|
moveq r2, r3
|
|
subne r0, r0, #4
|
|
|
|
@ Find the bit-offset of the match within the word. Note that the
|
|
@ bit result from clz will be 7 higher than "true", but we'll
|
|
@ immediately discard those bits converting to a byte offset.
|
|
#ifdef __ARMEL__
|
|
rev r2, r2 @ For LE, count from the little end
|
|
#endif
|
|
clz r2, r2
|
|
add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte
|
|
99:
|
|
sub r0, r0, r1 @ Subtract input to compute length
|
|
bx lr
|
|
|
|
END (strlen)
|
|
|
|
libc_hidden_builtin_def (strlen)
|