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/* Optimized strnlen implementation for PowerPC32/POWER7 using cmpb insn.
Copyright (C) 2010-2013 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
<http://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. */
ble L(small_range)
cmplw cr7,r3,r7 /* Is the address equal or less than r3? If
it's equal or less, it means size is either 0
or a negative number. */
ble cr7,L(proceed)
li r7,-1 /* Make r11 the biggest if r4 <= 0. */
L(proceed):
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. */
slw r10,r10,r6
srw r10,r10,r6
cmplwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
bne cr7,L(done)
/* Are we done already? */
addi r9,r8,4
cmplw cr6,r9,r7
bge cr6,L(end_max)
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 DWORD2 of pair. */
lwzu r12,4(r8)
cmpb r10,r12,r0
cmplwi cr7,r10,0
bne cr7,L(done)
/* Are we done already? */
addi r9,r8,4
cmplw cr6,r9,r7
bge cr6,L(end_max)
L(loop_setup):
sub r5,r7,r9
srwi r6,r5,3 /* Number of loop iterations. */
mtctr r6 /* Setup the counter. */
b L(loop)
/* Main loop to look for the null byte backwards 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're here because the counter reached 0, and that means we
didn't have any matches for null in the whole range. Just return
the original size. */
addi r9,r8,4
cmplw cr6,r9,r7
blt cr6,L(loop_small)
L(end_max):
sub r3,r7,r3
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):
cntlzw r0,r10 /* Count leading zeroes before the match. */
srwi r0,r0,3 /* Convert leading zeroes to bytes. */
add r9,r8,r0
sub r6,r9,r3 /* Length until the match. */
cmplw r9,r7
bgt L(end_max)
mr r3,r6
blr
.align 4
L(zero):
li r3,0
blr
/* Deals with size <= 32. */
.align 4
L(small_range):
cmplwi r4,0
beq L(zero)
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. */
slw r10,r10,r6
srw r10,r10,r6
cmplwi cr7,r10,0
bne cr7,L(done)
addi r9,r8,4
cmplw r9,r7
bge L(end_max)
b L(loop_small)
.p2align 5
L(loop_small):
lwzu r12,4(r8)
cmpb r10,r12,r0
addi r9,r8,4
cmplwi cr6,r10,0
bne cr6,L(done)
cmplw r9,r7
bge L(end_max)
b L(loop_small)
END (__strnlen)
weak_alias (__strnlen, strnlen)
libc_hidden_builtin_def (strnlen)
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