| /* strcat(dest, src) -- Append SRC on the end of DEST. |
| For Intel 80x86, x>=4. |
| Copyright (C) 1994-2016 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Ulrich Drepper <drepper@ipd.info.uni-karlsruhe.de>. |
| Optimised a little by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au> |
| |
| 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 |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include <sysdep.h> |
| #include "asm-syntax.h" |
| |
| #define PARMS 4+4 /* space for 1 saved reg */ |
| #define RTN PARMS |
| #define DEST RTN |
| #define SRC DEST+4 |
| |
| .text |
| ENTRY (strcat) |
| |
| pushl %edi /* Save callee-safe register. */ |
| cfi_adjust_cfa_offset (4) |
| |
| movl DEST(%esp), %edx |
| movl SRC(%esp), %ecx |
| |
| testb $0xff, (%ecx) /* Is source string empty? */ |
| jz L(8) /* yes => return */ |
| |
| /* Test the first bytes separately until destination is aligned. */ |
| testl $3, %edx /* destination pointer aligned? */ |
| jz L(1) /* yes => begin scan loop */ |
| testb $0xff, (%edx) /* is end of string? */ |
| jz L(2) /* yes => start appending */ |
| incl %edx /* increment source pointer */ |
| |
| testl $3, %edx /* destination pointer aligned? */ |
| jz L(1) /* yes => begin scan loop */ |
| testb $0xff, (%edx) /* is end of string? */ |
| jz L(2) /* yes => start appending */ |
| incl %edx /* increment source pointer */ |
| |
| testl $3, %edx /* destination pointer aligned? */ |
| jz L(1) /* yes => begin scan loop */ |
| testb $0xff, (%edx) /* is end of string? */ |
| jz L(2) /* yes => start appending */ |
| incl %edx /* increment source pointer */ |
| |
| /* Now we are aligned. Begin scan loop. */ |
| jmp L(1) |
| |
| cfi_rel_offset (edi, 0) |
| ALIGN(4) |
| |
| L(4): addl $16,%edx /* increment destination pointer for round */ |
| |
| L(1): movl (%edx), %eax /* get word (= 4 bytes) in question */ |
| movl $0xfefefeff, %edi /* magic value */ |
| |
| /* If you compare this with the algorithm in memchr.S you will |
| notice that here is an `xorl' statement missing. But you must |
| not forget that we are looking for C == 0 and `xorl $0, %eax' |
| is a no-op. */ |
| |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| |
| /* According to the algorithm we had to reverse the effect of the |
| XOR first and then test the overflow bits. But because the |
| following XOR would destroy the carry flag and it would (in a |
| representation with more than 32 bits) not alter then last |
| overflow, we can now test this condition. If no carry is signaled |
| no overflow must have occurred in the last byte => it was 0. */ |
| jnc L(3) |
| |
| /* We are only interested in carry bits that change due to the |
| previous add, so remove original bits */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| |
| /* Now test for the other three overflow bits. */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| |
| /* If at least one byte of the word is C we don't get 0 in %ecx. */ |
| jnz L(3) |
| |
| movl 4(%edx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(5) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz L(5) /* one byte is NUL => stop copying */ |
| |
| movl 8(%edx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(6) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz L(6) /* one byte is NUL => stop copying */ |
| |
| movl 12(%edx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(7) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jz L(4) /* no byte is NUL => carry on copying */ |
| |
| L(7): addl $4, %edx /* adjust source pointer */ |
| L(6): addl $4, %edx |
| L(5): addl $4, %edx |
| |
| L(3): testb %al, %al /* is first byte NUL? */ |
| jz L(2) /* yes => start copying */ |
| incl %edx /* increment source pointer */ |
| |
| testb %ah, %ah /* is second byte NUL? */ |
| jz L(2) /* yes => start copying */ |
| incl %edx /* increment source pointer */ |
| |
| testl $0xff0000, %eax /* is third byte NUL? */ |
| jz L(2) /* yes => start copying */ |
| incl %edx /* increment source pointer */ |
| |
| L(2): subl %ecx, %edx /* reduce number of loop variants */ |
| |
| /* Now we have to align the source pointer. */ |
| testl $3, %ecx /* pointer correctly aligned? */ |
| jz L(29) /* yes => start copy loop */ |
| movb (%ecx), %al /* get first byte */ |
| movb %al, (%ecx,%edx) /* and store it */ |
| andb %al, %al /* is byte NUL? */ |
| jz L(8) /* yes => return */ |
| incl %ecx /* increment pointer */ |
| |
| testl $3, %ecx /* pointer correctly aligned? */ |
| jz L(29) /* yes => start copy loop */ |
| movb (%ecx), %al /* get first byte */ |
| movb %al, (%ecx,%edx) /* and store it */ |
| andb %al, %al /* is byte NUL? */ |
| jz L(8) /* yes => return */ |
| incl %ecx /* increment pointer */ |
| |
| testl $3, %ecx /* pointer correctly aligned? */ |
| jz L(29) /* yes => start copy loop */ |
| movb (%ecx), %al /* get first byte */ |
| movb %al, (%ecx,%edx) /* and store it */ |
| andb %al, %al /* is byte NUL? */ |
| jz L(8) /* yes => return */ |
| incl %ecx /* increment pointer */ |
| |
| /* Now we are aligned. */ |
| jmp L(29) /* start copy loop */ |
| |
| ALIGN(4) |
| |
| L(28): movl %eax, 12(%ecx,%edx)/* store word at destination */ |
| addl $16, %ecx /* adjust pointer for full round */ |
| |
| L(29): movl (%ecx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(9) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz L(9) /* one byte is NUL => stop copying */ |
| movl %eax, (%ecx,%edx) /* store word to destination */ |
| |
| movl 4(%ecx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(91) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz L(91) /* one byte is NUL => stop copying */ |
| movl %eax, 4(%ecx,%edx) /* store word to destination */ |
| |
| movl 8(%ecx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(92) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jnz L(92) /* one byte is NUL => stop copying */ |
| movl %eax, 8(%ecx,%edx) /* store word to destination */ |
| |
| movl 12(%ecx), %eax /* get word from source */ |
| movl $0xfefefeff, %edi /* magic value */ |
| addl %eax, %edi /* add the magic value to the word. We get |
| carry bits reported for each byte which |
| is *not* 0 */ |
| jnc L(93) /* highest byte is C => stop copying */ |
| xorl %eax, %edi /* ((word^charmask)+magic)^(word^charmask) */ |
| orl $0xfefefeff, %edi /* set all non-carry bits */ |
| incl %edi /* add 1: if one carry bit was *not* set |
| the addition will not result in 0. */ |
| jz L(28) /* no is NUL => carry on copying */ |
| |
| L(93): addl $4, %ecx /* adjust pointer */ |
| L(92): addl $4, %ecx |
| L(91): addl $4, %ecx |
| |
| L(9): movb %al, (%ecx,%edx) /* store first byte of last word */ |
| orb %al, %al /* is it NUL? */ |
| jz L(8) /* yes => return */ |
| |
| movb %ah, 1(%ecx,%edx) /* store second byte of last word */ |
| orb %ah, %ah /* is it NUL? */ |
| jz L(8) /* yes => return */ |
| |
| shrl $16, %eax /* make upper bytes accessible */ |
| movb %al, 2(%ecx,%edx) /* store third byte of last word */ |
| orb %al, %al /* is it NUL? */ |
| jz L(8) /* yes => return */ |
| |
| movb %ah, 3(%ecx,%edx) /* store fourth byte of last word */ |
| |
| L(8): movl DEST(%esp), %eax /* start address of destination is result */ |
| popl %edi /* restore saved register */ |
| cfi_adjust_cfa_offset (-4) |
| cfi_restore (edi) |
| |
| ret |
| END (strcat) |
| libc_hidden_builtin_def (strcat) |