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264 lines
9.5 KiB
ArmAsm
264 lines
9.5 KiB
ArmAsm
/* strcat(dest, src) -- Append SRC on the end of DEST.
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For Intel 80x86, x>=4.
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Copyright (C) 1994-2023 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+4 /* space for 1 saved reg */
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#define RTN PARMS
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#define DEST RTN
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#define SRC DEST+4
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.text
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ENTRY (strcat)
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pushl %edi /* Save callee-safe register. */
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cfi_adjust_cfa_offset (4)
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movl DEST(%esp), %edx
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movl SRC(%esp), %ecx
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testb $0xff, (%ecx) /* Is source string empty? */
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jz L(8) /* yes => return */
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/* Test the first bytes separately until destination is aligned. */
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testl $3, %edx /* destination pointer aligned? */
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jz L(1) /* yes => begin scan loop */
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testb $0xff, (%edx) /* is end of string? */
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jz L(2) /* yes => start appending */
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incl %edx /* increment source pointer */
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testl $3, %edx /* destination pointer aligned? */
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jz L(1) /* yes => begin scan loop */
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testb $0xff, (%edx) /* is end of string? */
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jz L(2) /* yes => start appending */
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incl %edx /* increment source pointer */
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testl $3, %edx /* destination pointer aligned? */
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jz L(1) /* yes => begin scan loop */
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testb $0xff, (%edx) /* is end of string? */
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jz L(2) /* yes => start appending */
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incl %edx /* increment source pointer */
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/* Now we are aligned. Begin scan loop. */
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jmp L(1)
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cfi_rel_offset (edi, 0)
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ALIGN(4)
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L(4): addl $16,%edx /* increment destination pointer for round */
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L(1): movl (%edx), %eax /* get word (= 4 bytes) in question */
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movl $0xfefefeff, %edi /* magic value */
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/* If you compare this with the algorithm in memchr.S you will
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notice that here is an `xorl' statement missing. But you must
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not forget that we are looking for C == 0 and `xorl $0, %eax'
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is a no-op. */
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addl %eax, %edi /* 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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/* According to the algorithm we had to reverse the effect of the
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XOR first and then test the overflow bits. But because the
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following XOR would destroy the carry flag and it would (in a
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representation with more than 32 bits) not alter then last
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overflow, we can now test this condition. If no carry is signaled
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no overflow must have occurred in the last byte => it was 0. */
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jnc L(3)
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/* We are only interested in carry bits that change due to the
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previous add, so remove original bits */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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/* Now test for the other three overflow bits. */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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/* If at least one byte of the word is C we don't get 0 in %ecx. */
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jnz L(3)
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movl 4(%edx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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 C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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) /* one byte is NUL => stop copying */
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movl 8(%edx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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 C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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) /* one byte is NUL => stop copying */
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movl 12(%edx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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 C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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 byte is NUL => carry on copying */
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L(7): addl $4, %edx /* adjust source pointer */
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L(6): addl $4, %edx
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L(5): addl $4, %edx
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L(3): testb %al, %al /* is first byte NUL? */
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jz L(2) /* yes => start copying */
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incl %edx /* increment source pointer */
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testb %ah, %ah /* is second byte NUL? */
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jz L(2) /* yes => start copying */
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incl %edx /* increment source pointer */
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testl $0xff0000, %eax /* is third byte NUL? */
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jz L(2) /* yes => start copying */
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incl %edx /* increment source pointer */
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L(2): subl %ecx, %edx /* reduce number of loop variants */
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/* Now we have to align the source pointer. */
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testl $3, %ecx /* pointer correctly aligned? */
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jz L(29) /* yes => start copy loop */
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movb (%ecx), %al /* get first byte */
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movb %al, (%ecx,%edx) /* and store it */
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andb %al, %al /* is byte NUL? */
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jz L(8) /* yes => return */
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incl %ecx /* increment pointer */
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testl $3, %ecx /* pointer correctly aligned? */
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jz L(29) /* yes => start copy loop */
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movb (%ecx), %al /* get first byte */
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movb %al, (%ecx,%edx) /* and store it */
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andb %al, %al /* is byte NUL? */
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jz L(8) /* yes => return */
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incl %ecx /* increment pointer */
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testl $3, %ecx /* pointer correctly aligned? */
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jz L(29) /* yes => start copy loop */
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movb (%ecx), %al /* get first byte */
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movb %al, (%ecx,%edx) /* and store it */
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andb %al, %al /* is byte NUL? */
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jz L(8) /* yes => return */
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incl %ecx /* increment pointer */
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/* Now we are aligned. */
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jmp L(29) /* start copy loop */
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ALIGN(4)
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L(28): movl %eax, 12(%ecx,%edx)/* store word at destination */
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addl $16, %ecx /* adjust pointer for full round */
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L(29): movl (%ecx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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(9) /* highest byte is C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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(9) /* one byte is NUL => stop copying */
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movl %eax, (%ecx,%edx) /* store word to destination */
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movl 4(%ecx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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(91) /* highest byte is C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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(91) /* one byte is NUL => stop copying */
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movl %eax, 4(%ecx,%edx) /* store word to destination */
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movl 8(%ecx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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(92) /* highest byte is C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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(92) /* one byte is NUL => stop copying */
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movl %eax, 8(%ecx,%edx) /* store word to destination */
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movl 12(%ecx), %eax /* get word from source */
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movl $0xfefefeff, %edi /* magic value */
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addl %eax, %edi /* 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(93) /* highest byte is C => stop copying */
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xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* 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(28) /* no is NUL => carry on copying */
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L(93): addl $4, %ecx /* adjust pointer */
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L(92): addl $4, %ecx
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L(91): addl $4, %ecx
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L(9): movb %al, (%ecx,%edx) /* store first byte of last word */
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orb %al, %al /* is it NUL? */
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jz L(8) /* yes => return */
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movb %ah, 1(%ecx,%edx) /* store second byte of last word */
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orb %ah, %ah /* is it NUL? */
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jz L(8) /* yes => return */
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shrl $16, %eax /* make upper bytes accessible */
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movb %al, 2(%ecx,%edx) /* store third byte of last word */
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orb %al, %al /* is it NUL? */
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jz L(8) /* yes => return */
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movb %ah, 3(%ecx,%edx) /* store fourth byte of last word */
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L(8): movl DEST(%esp), %eax /* start address of destination is result */
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popl %edi /* restore saved register */
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cfi_adjust_cfa_offset (-4)
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cfi_restore (edi)
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ret
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END (strcat)
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libc_hidden_builtin_def (strcat)
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