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/* Optimized strnlen implementation for PowerPC64/POWER7 using cmpb insn.
Copyright (C) 2010-2021 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>
#ifndef STRNLEN
# define STRNLEN __strnlen
#endif
/* int [r3] strnlen (char *s [r3], int size [r4]) */
.machine power7
ENTRY_TOCLESS (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. */
addi r7,r7,-1
/* If we have less than 33 bytes to search, skip to a faster code. */
ble L(small_range)
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. */
#ifdef __LITTLE_ENDIAN__
srd r10,r10,r6
sld r10,r10,r6
#else
sld r10,r10,r6
srd r10,r10,r6
#endif
cmpldi cr7,r10,0 /* If r10 == 0, no null's have been found. */
bne cr7,L(done)
clrrdi r7,r7,3 /* Address of last doubleword. */
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)
L(loop_setup):
/* The last dword we want to read in the loop below is the one
containing the last byte of the string, ie. the dword at
(s + size - 1) & ~7, or r7. The first dword read is at
r8 + 8, we read 2 * cnt dwords, so the last dword read will
be at r8 + 8 + 16 * cnt - 8. Solving for cnt gives
cnt = (r7 - r8) / 16 */
sub r5,r7,r8
srdi r6,r5,4 /* 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 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 may have one more dword to read. */
cmpld cr6,r8,r7
beq cr6,L(end_max)
ldu r12,8(r8)
cmpb r10,r12,r0
cmpldi cr6,r10,0
bne cr6,L(done)
L(end_max):
mr r3,r4
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 end of the
range. */
L(done):
#ifdef __LITTLE_ENDIAN__
addi r0,r10,-1
andc r0,r0,r10
popcntd r0,r0
#else
cntlzd r0,r10 /* Count leading zeros before the match. */
#endif
sub r3,r8,r3
srdi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
add r3,r3,r0 /* Length until the match. */
cmpld r3,r4
blelr
mr r3,r4
blr
/* Deals with size <= 32. */
.align 4
L(small_range):
cmpldi r4,0
beq L(end_max)
clrrdi r7,r7,3 /* Address of last doubleword. */
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. */
#ifdef __LITTLE_ENDIAN__
srd r10,r10,r6
sld r10,r10,r6
#else
sld r10,r10,r6
srd r10,r10,r6
#endif
cmpldi cr7,r10,0
bne cr7,L(done)
cmpld r8,r7
beq L(end_max)
.p2align 5
L(loop_small):
ldu r12,8(r8)
cmpb r10,r12,r0
cmpldi cr6,r10,0
bne cr6,L(done)
cmpld r8,r7
bne L(loop_small)
mr r3,r4
blr
END (STRNLEN)
libc_hidden_def (__strnlen)
weak_alias (__strnlen, strnlen)
libc_hidden_def (strnlen)
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