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/* Optimized strlen 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] strlen (char *s [r3]) */
.machine power7
ENTRY (strlen)
CALL_MCOUNT
dcbt 0,r3
clrrwi r4,r3,2 /* Align the address to word boundary. */
rlwinm r6,r3,3,27,28 /* Calculate padding. */
li r0,0 /* Word with null chars to use with cmpb. */
li r5,-1 /* MASK = 0xffffffffffffffff. */
lwz r12,0(r4) /* Load word from memory. */
#ifdef __LITTLE_ENDIAN__
slw r5,r5,r6
#else
srw r5,r5,r6 /* MASK = MASK >> padding. */
#endif
orc r9,r12,r5 /* Mask bits that are not part of the string. */
cmpb r10,r9,r0 /* Check for null bytes in WORD1. */
cmpwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
bne cr7,L(done)
mtcrf 0x01,r4
/* 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)
/* Handle WORD2 of pair. */
lwzu r12,4(r4)
cmpb r10,r12,r0
cmpwi cr7,r10,0
bne cr7,L(done)
/* Main loop to look for the end of 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(r4)
lwzu r11, 8(r4)
cmpb r10,r12,r0
cmpb r9,r11,r0
or r8,r9,r10 /* Merge everything in one word. */
cmpwi cr7,r8,0
beq cr7,L(loop)
/* 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. */
cmpwi cr6,r10,0
addi r4,r4,-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 r4,r4,4
/* 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. */
L(done):
#ifdef __LITTLE_ENDIAN__
addi r9, r10, -1 /* Form a mask from trailing zeros. */
andc r9, r9, r10
popcntw r0, r9 /* Count the bits in the mask. */
#else
cntlzw r0,r10 /* Count leading zeros before the match. */
#endif
subf r5,r3,r4
srwi r0,r0,3 /* Convert leading zeros to bytes. */
add r3,r5,r0 /* Compute final length. */
blr
END (strlen)
libc_hidden_builtin_def (strlen)
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