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/* Optimized version of the standard strlen() function.
This file is part of the GNU C Library.
Copyright (C) 2000-2024 Free Software Foundation, Inc.
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/>. */
/* Return: the length of the input string
Input:
in0: str
Look for the null character byte by byte, until we reach a word aligned
address, then search word by word, using the czx instruction. We're
also doing one word of read ahead, which could cause problems if the
null character is on the last word of a page and the next page is not
mapped in the process address space. Hence the use of the speculative
load.
This implementation assumes little endian mode. For big endian mode,
the instruction czx1.r should be replaced by czx1.l. */
#include <sysdep.h>
#undef ret
#define saved_lc r18
#define str r19
#define pos0 r20
#define val1 r21
#define val2 r22
#define origadd r23
#define tmp r24
#define loopcnt r30
#define len ret0
ENTRY(strlen)
.prologue
alloc r2 = ar.pfs, 1, 0, 0, 0
.save ar.lc, saved_lc
mov saved_lc = ar.lc // save the loop counter
.body
mov str = in0
mov len = r0 // len = 0
and tmp = 7, in0 // tmp = str % 8
;;
sub loopcnt = 8, tmp // loopcnt = 8 - tmp
cmp.eq p6, p0 = tmp, r0
(p6) br.cond.sptk .str_aligned;;
adds loopcnt = -1, loopcnt;;
mov ar.lc = loopcnt
.l1:
ld1 val2 = [str], 1
;;
cmp.eq p6, p0 = val2, r0
(p6) br.cond.spnt .restore_and_exit
adds len = 1, len
br.cloop.dptk .l1
.str_aligned:
mov origadd = str // origadd = orig
ld8 val1 = [str], 8;;
nop.b 0
nop.b 0
.l2: ld8.s val2 = [str], 8 // don't bomb out here
czx1.r pos0 = val1
;;
cmp.ne p6, p0 = 8, pos0
(p6) br.cond.spnt .foundit
chk.s val2, .recovery
.back:
mov val1 = val2
br.cond.dptk .l2
.foundit:
sub tmp = str, origadd // tmp = crt address - orig
add len = len, pos0;;
add len = len, tmp;;
adds len = -16, len
.restore_and_exit:
mov ar.lc = saved_lc // restore the loop counter
br.ret.sptk.many b0
.recovery:
adds str = -8, str;;
ld8 val2 = [str], 8 // bomb out here
br.cond.sptk .back
END(strlen)
libc_hidden_builtin_def (strlen)
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