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/* Optimized strnlen implementation for PowerPC64/POWER7 using cmpb insn.
Copyright (C) 2010 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>
#include <bp-sym.h>
#include <bp-asm.h>
/* int [r3] strnlen (char *s [r3], int size [r4]) */
.machine power7
ENTRY (BP_SYM (__strnlen))
CALL_MCOUNT 2
dcbt 0,r3
clrrdi r8,r3,3
add r7,r3,r4 /* Calculate the last acceptable address. */
cmpldi r4,32
li r0,0 /* Doubleword with null chars. */
/* If we have less than 33 bytes to search, skip to a faster code. */
ble L(small_range)
cmpld 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,r3,3,26,28 /* Calculate padding. */
ld r12,0(r8) /* Load doubleword from memory. */
cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
sld r10,r10,r6
srd r10,r10,r6
cmpldi cr7,r10,0 /* If r10 == 0, no null's have been found. */
bne cr7,L(done)
/* Are we done already? */
addi r9,r8,8
cmpld cr6,r9,r7
bge cr6,L(end_max)
mtcrf 0x01,r8
/* Are we now aligned to a quadword boundary? If so, skip to
the main loop. Otherwise, go through the alignment code. */
bt 28,L(loop_setup)
/* Handle DWORD2 of pair. */
ldu r12,8(r8)
cmpb r10,r12,r0
cmpldi cr7,r10,0
bne cr7,L(done)
/* Are we done already? */
addi r9,r8,8
cmpld cr6,r9,r7
bge cr6,L(end_max)
L(loop_setup):
sub r5,r7,r9
srdi r6,r5,4 /* 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 doublewords, compare and merge in a
single register for speed. This is an attempt
to speed up the null-checking process for bigger strings. */
ld r12,8(r8)
ldu r11,16(r8)
cmpb r10,r12,r0
cmpb r9,r11,r0
or r5,r9,r10 /* Merge everything in one doubleword. */
cmpldi 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,r8,8
cmpld cr6,r9,r7
blt cr6,L(loop_small)
L(end_max):
sub r3,r7,r3
blr
/* OK, one (or both) of the doublewords contains a null byte. Check
the first doubleword and decrement the address in case the first
doubleword really contains a null byte. */
.align 4
L(found):
cmpldi cr6,r10,0
addi r8,r8,-8
bne cr6,L(done)
/* The null byte must be in the second doubleword. Adjust the address
again and move the result of cmpb to r10 so we can calculate the
length. */
mr r10,r9
addi r8,r8,8
/* r10 has the output of the cmpb instruction, that is, it contains
0xff in the same position as the null byte in the original
doubleword from the string. Use that to calculate the length.
We need to make sure the null char is *before* the start of the
range (since we're going backwards). */
L(done):
cntlzd r0,r10 /* Count leading zeroes before the match. */
srdi r0,r0,3 /* Convert leading zeroes to bytes. */
add r9,r8,r0
sub r6,r9,r3 /* Length until the match. */
cmpld 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):
cmpldi r4,0
beq L(zero)
rlwinm r6,r3,3,26,28 /* Calculate padding. */
ld r12,0(r8) /* Load word from memory. */
cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
sld r10,r10,r6
srd r10,r10,r6
cmpldi cr7,r10,0
bne cr7,L(done)
addi r9,r8,8
cmpld r9,r7
bge L(end_max)
b L(loop_small)
.p2align 5
L(loop_small):
ldu r12,8(r8)
cmpb r10,r12,r0
addi r9,r8,8
cmpldi cr6,r10,0
bne cr6,L(done)
cmpld r9,r7
bge L(end_max)
b L(loop_small)
END (BP_SYM (__strnlen))
weak_alias (BP_SYM (__strnlen), BP_SYM(strnlen))
libc_hidden_builtin_def (strnlen)
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