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/* Optimized strnlen implementation for PowerPC32/POWER7 using cmpb insn.
Copyright (C) 2010-2020 Free Software Foundation, Inc.
Contributed by Luis Machado <luisgpm@br.ibm.com>.
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
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* int [r3] strnlen (char *s [r3], int size [r4]) */
.machine power7
ENTRY (__strnlen)
CALL_MCOUNT
dcbt 0,r3
clrrwi r8,r3,2 /* Align the address to word boundary. */
add r7,r3,r4 /* Calculate the last acceptable address. */
cmplwi r4,16
li r0,0 /* Word with null chars. */
addi r7,r7,-1
ble L(small_range)
rlwinm r6,r3,3,27,28 /* Calculate padding. */
lwz r12,0(r8) /* Load word from memory. */
cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
#ifdef __LITTLE_ENDIAN__
srw r10,r10,r6
slw r10,r10,r6
#else
slw r10,r10,r6
srw r10,r10,r6
#endif
cmplwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
bne cr7,L(done)
clrrwi r7,r7,2 /* Address of last word. */
mtcrf 0x01,r8
/* Are we now aligned to a doubleword boundary? If so, skip to
the main loop. Otherwise, go through the alignment code. */
bt 29,L(loop_setup)
/* Handle WORD2 of pair. */
lwzu r12,4(r8)
cmpb r10,r12,r0
cmplwi cr7,r10,0
bne cr7,L(done)
L(loop_setup):
/* The last word we want to read in the loop below is the one
containing the last byte of the string, ie. the word at
(s + size - 1) & ~3, or r7. The first word read is at
r8 + 4, we read 2 * cnt words, so the last word read will
be at r8 + 4 + 8 * cnt - 4. Solving for cnt gives
cnt = (r7 - r8) / 8 */
sub r5,r7,r8
srwi r6,r5,3 /* Number of loop iterations. */
mtctr r6 /* Setup the counter. */
/* Main loop to look for the null byte in the string. Since
it's a small loop (< 8 instructions), align it to 32-bytes. */
.p2align 5
L(loop):
/* Load two words, compare and merge in a
single register for speed. This is an attempt
to speed up the null-checking process for bigger strings. */
lwz r12,4(r8)
lwzu r11,8(r8)
cmpb r10,r12,r0
cmpb r9,r11,r0
or r5,r9,r10 /* Merge everything in one word. */
cmplwi cr7,r5,0
bne cr7,L(found)
bdnz L(loop)
/* We may have one more word to read. */
cmplw cr6,r8,r7
beq cr6,L(end_max)
lwzu r12,4(r8)
cmpb r10,r12,r0
cmplwi cr6,r10,0
bne cr6,L(done)
L(end_max):
mr r3,r4
blr
/* OK, one (or both) of the words contains a null byte. Check
the first word and decrement the address in case the first
word really contains a null byte. */
.align 4
L(found):
cmplwi cr6,r10,0
addi r8,r8,-4
bne cr6,L(done)
/* The null byte must be in the second word. Adjust the address
again and move the result of cmpb to r10 so we can calculate the
length. */
mr r10,r9
addi r8,r8,4
/* r10 has the output of the cmpb instruction, that is, it contains
0xff in the same position as the null byte in the original
word from the string. Use that to calculate the length.
We need to make sure the null char is *before* the end of the
range. */
L(done):
#ifdef __LITTLE_ENDIAN__
addi r0,r10,-1
andc r0,r0,r10
popcntw r0,r0
#else
cntlzw r0,r10 /* Count leading zeros before the match. */
#endif
sub r3,r8,r3
srwi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
add r3,r3,r0 /* Length until the match. */
cmplw r3,r4
blelr
mr r3,r4
blr
/* Deals with size <= 16. */
.align 4
L(small_range):
cmplwi r4,0
beq L(end_max)
clrrwi r7,r7,2 /* Address of last word. */
rlwinm r6,r3,3,27,28 /* Calculate padding. */
lwz r12,0(r8) /* Load word from memory. */
cmpb r10,r12,r0 /* Check for null bytes in WORD1. */
#ifdef __LITTLE_ENDIAN__
srw r10,r10,r6
slw r10,r10,r6
#else
slw r10,r10,r6
srw r10,r10,r6
#endif
cmplwi cr7,r10,0
bne cr7,L(done)
cmplw r8,r7
beq L(end_max)
.p2align 5
L(loop_small):
lwzu r12,4(r8)
cmpb r10,r12,r0
cmplwi cr6,r10,0
bne cr6,L(done)
cmplw r8,r7
bne L(loop_small)
mr r3,r4
blr
END (__strnlen)
libc_hidden_def (__strnlen)
weak_alias (__strnlen, strnlen)
libc_hidden_builtin_def (strnlen)
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