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30891f35fa
We stopped adding "Contributed by" or similar lines in sources in 2012 in favour of git logs and keeping the Contributors section of the glibc manual up to date. Removing these lines makes the license header a bit more consistent across files and also removes the possibility of error in attribution when license blocks or files are copied across since the contributed-by lines don't actually reflect reality in those cases. Move all "Contributed by" and similar lines (Written by, Test by, etc.) into a new file CONTRIBUTED-BY to retain record of these contributions. These contributors are also mentioned in manual/contrib.texi, so we just maintain this additional record as a courtesy to the earlier developers. The following scripts were used to filter a list of files to edit in place and to clean up the CONTRIBUTED-BY file respectively. These were not added to the glibc sources because they're not expected to be of any use in future given that this is a one time task: https://gist.github.com/siddhesh/b5ecac94eabfd72ed2916d6d8157e7dc https://gist.github.com/siddhesh/15ea1f5e435ace9774f485030695ee02 Reviewed-by: Carlos O'Donell <carlos@redhat.com>
132 lines
4.8 KiB
ArmAsm
132 lines
4.8 KiB
ArmAsm
/* strlen(str) -- determine the length of the string STR.
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Optimized for Intel 80x86, x>=4.
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Copyright (C) 1991-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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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#include <sysdep.h>
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#include "asm-syntax.h"
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#define PARMS 4 /* no space for saved regs */
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#define STR PARMS
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.text
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ENTRY (strlen)
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movl STR(%esp), %ecx
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movl %ecx, %eax /* duplicate it */
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andl $3, %ecx /* mask alignment bits */
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jz L(1) /* aligned => start loop */
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cmpb %ch, (%eax) /* is byte NUL? */
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je L(2) /* yes => return */
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incl %eax /* increment pointer */
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xorl $3, %ecx /* was alignment = 3? */
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jz L(1) /* yes => now it is aligned and start loop */
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cmpb %ch, (%eax) /* is byte NUL? */
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je L(2) /* yes => return */
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addl $1, %eax /* increment pointer */
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subl $1, %ecx /* was alignment = 2? */
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jz L(1) /* yes => now it is aligned and start loop */
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cmpb %ch, (%eax) /* is byte NUL? */
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je L(2) /* yes => return */
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/* Don't change the above `addl $1,%eax' and `subl $1, %ecx' into `incl %eax'
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and `decl %ecx' resp. The additional two byte per instruction make the
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label 4 to be aligned on a 16 byte boundary with nops.
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The following `sub $15, %eax' is part of this trick, too. Together with
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the next instruction (`addl $16, %eax') it is in fact a `incl %eax', just
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as expected from the algorithm. But doing so has the advantage that
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no jump to label 1 is necessary and so the pipeline is not flushed. */
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subl $15, %eax /* effectively +1 */
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L(4): addl $16, %eax /* adjust pointer for full loop */
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L(1): movl (%eax), %ecx /* get word (= 4 bytes) in question */
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movl $0xfefefeff, %edx /* magic value */
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addl %ecx, %edx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(3) /* highest byte is NUL => return pointer */
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xorl %ecx, %edx /* (word+magic)^word */
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orl $0xfefefeff, %edx /* set all non-carry bits */
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incl %edx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(3) /* found NUL => return pointer */
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movl 4(%eax), %ecx /* get word (= 4 bytes) in question */
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movl $0xfefefeff, %edx /* magic value */
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addl %ecx, %edx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(5) /* highest byte is NUL => return pointer */
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xorl %ecx, %edx /* (word+magic)^word */
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orl $0xfefefeff, %edx /* set all non-carry bits */
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incl %edx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(5) /* found NUL => return pointer */
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movl 8(%eax), %ecx /* get word (= 4 bytes) in question */
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movl $0xfefefeff, %edx /* magic value */
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addl %ecx, %edx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(6) /* highest byte is NUL => return pointer */
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xorl %ecx, %edx /* (word+magic)^word */
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orl $0xfefefeff, %edx /* set all non-carry bits */
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incl %edx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(6) /* found NUL => return pointer */
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movl 12(%eax), %ecx /* get word (= 4 bytes) in question */
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movl $0xfefefeff, %edx /* magic value */
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addl %ecx, %edx /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(7) /* highest byte is NUL => return pointer */
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xorl %ecx, %edx /* (word+magic)^word */
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orl $0xfefefeff, %edx /* set all non-carry bits */
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incl %edx /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jz L(4) /* no NUL found => continue loop */
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L(7): addl $4, %eax /* adjust pointer */
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L(6): addl $4, %eax
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L(5): addl $4, %eax
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L(3): testb %cl, %cl /* is first byte NUL? */
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jz L(2) /* yes => return */
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incl %eax /* increment pointer */
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testb %ch, %ch /* is second byte NUL? */
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jz L(2) /* yes => return */
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incl %eax /* increment pointer */
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testl $0xff0000, %ecx /* is third byte NUL? */
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jz L(2) /* yes => return pointer */
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incl %eax /* increment pointer */
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L(2): subl STR(%esp), %eax /* compute difference to string start */
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ret
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END (strlen)
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libc_hidden_builtin_def (strlen)
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