97 lines
2.7 KiB
ArmAsm
97 lines
2.7 KiB
ArmAsm
/* Optimized version of the standard strlen() function.
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This file is part of the GNU C Library.
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Copyright (C) 2000-2022 Free Software Foundation, Inc.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* Return: the length of the input string
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Input:
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in0: str
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Look for the null character byte by byte, until we reach a word aligned
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address, then search word by word, using the czx instruction. We're
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also doing one word of read ahead, which could cause problems if the
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null character is on the last word of a page and the next page is not
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mapped in the process address space. Hence the use of the speculative
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load.
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This implementation assumes little endian mode. For big endian mode,
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the instruction czx1.r should be replaced by czx1.l. */
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#include <sysdep.h>
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#undef ret
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#define saved_lc r18
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#define str r19
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#define pos0 r20
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#define val1 r21
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#define val2 r22
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#define origadd r23
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#define tmp r24
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#define loopcnt r30
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#define len ret0
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ENTRY(strlen)
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.prologue
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alloc r2 = ar.pfs, 1, 0, 0, 0
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.save ar.lc, saved_lc
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mov saved_lc = ar.lc // save the loop counter
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.body
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mov str = in0
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mov len = r0 // len = 0
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and tmp = 7, in0 // tmp = str % 8
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;;
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sub loopcnt = 8, tmp // loopcnt = 8 - tmp
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cmp.eq p6, p0 = tmp, r0
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(p6) br.cond.sptk .str_aligned;;
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adds loopcnt = -1, loopcnt;;
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mov ar.lc = loopcnt
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.l1:
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ld1 val2 = [str], 1
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;;
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cmp.eq p6, p0 = val2, r0
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(p6) br.cond.spnt .restore_and_exit
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adds len = 1, len
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br.cloop.dptk .l1
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.str_aligned:
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mov origadd = str // origadd = orig
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ld8 val1 = [str], 8;;
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nop.b 0
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nop.b 0
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.l2: ld8.s val2 = [str], 8 // don't bomb out here
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czx1.r pos0 = val1
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;;
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cmp.ne p6, p0 = 8, pos0
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(p6) br.cond.spnt .foundit
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chk.s val2, .recovery
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.back:
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mov val1 = val2
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br.cond.dptk .l2
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.foundit:
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sub tmp = str, origadd // tmp = crt address - orig
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add len = len, pos0;;
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add len = len, tmp;;
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adds len = -16, len
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.restore_and_exit:
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mov ar.lc = saved_lc // restore the loop counter
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br.ret.sptk.many b0
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.recovery:
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adds str = -8, str;;
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ld8 val2 = [str], 8 // bomb out here
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br.cond.sptk .back
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END(strlen)
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libc_hidden_builtin_def (strlen)
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