diff options
Diffstat (limited to 'sysdeps/i386/strcat.S')
| -rw-r--r-- | sysdeps/i386/strcat.S | 265 |
1 files changed, 265 insertions, 0 deletions
diff --git a/sysdeps/i386/strcat.S b/sysdeps/i386/strcat.S new file mode 100644 index 0000000000..3abc35b072 --- /dev/null +++ b/sysdeps/i386/strcat.S @@ -0,0 +1,265 @@ +/* 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) |