/* strcat(dest, src) -- Append SRC on the end of DEST. For Intel 80x86, x>=4. Copyright (C) 1994, 1995, 1996 Free Software Foundation, Inc. Contributed by Ulrich Drepper . Optimised a little by Alan Modra This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 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 Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with the GNU C Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include #include "asm-syntax.h" /* INPUT PARAMETERS: dest (sp + 4) src (sp + 8) */ .text ENTRY (strcat) pushl %edi /* Save callee-safe register. */ movl 12(%esp), %ecx /* load source pointer */ movl 8(%esp), %edx /* load destination pointer */ testb $0xff, (%ecx) /* Is source string empty? */ jz L8 /* yes => return */ /* Test the first bytes separately until destination is aligned. */ testl $3, %edx /* destination pointer aligned? */ jz L1 /* yes => begin scan loop */ testb $0xff, (%edx) /* is end of string? */ jz L2 /* yes => start appending */ incl %edx /* increment source pointer */ testl $3, %edx /* destination pointer aligned? */ jz L1 /* yes => begin scan loop */ testb $0xff, (%edx) /* is end of string? */ jz L2 /* yes => start appending */ incl %edx /* increment source pointer */ testl $3, %edx /* destination pointer aligned? */ jz L1 /* yes => begin scan loop */ testb $0xff, (%edx) /* is end of string? */ jz L2 /* yes => start appending */ incl %edx /* increment source pointer */ /* Now we are aligned. Begin scan loop. */ jmp L1 ALIGN(4) L4: addl $16,%edx /* increment destination pointer for round */ L1: 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 occured in the last byte => it was 0. */ jnc L3 /* 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 L3 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 L5 /* 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 L5 /* 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 L6 /* 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 L6 /* 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 L7 /* 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 L4 /* no byte is NUL => carry on copying */ L7: addl $4, %edx /* adjust source pointer */ L6: addl $4, %edx L5: addl $4, %edx L3: testb %al, %al /* is first byte NUL? */ jz L2 /* yes => start copying */ incl %edx /* increment source pointer */ testb %ah, %ah /* is second byte NUL? */ jz L2 /* yes => start copying */ incl %edx /* increment source pointer */ testl $0xff0000, %eax /* is third byte NUL? */ jz L2 /* yes => start copying */ incl %edx /* increment source pointer */ L2: subl %ecx, %edx /* reduce number of loop variants */ /* Now we have to align the source pointer. */ testl $3, %ecx /* pointer correctly aligned? */ jz L29 /* yes => start copy loop */ movb (%ecx), %al /* get first byte */ movb %al, (%ecx,%edx) /* and store it */ andb %al, %al /* is byte NUL? */ jz L8 /* yes => return */ incl %ecx /* increment pointer */ testl $3, %ecx /* pointer correctly aligned? */ jz L29 /* yes => start copy loop */ movb (%ecx), %al /* get first byte */ movb %al, (%ecx,%edx) /* and store it */ andb %al, %al /* is byte NUL? */ jz L8 /* yes => return */ incl %ecx /* increment pointer */ testl $3, %ecx /* pointer correctly aligned? */ jz L29 /* yes => start copy loop */ movb (%ecx), %al /* get first byte */ movb %al, (%ecx,%edx) /* and store it */ andb %al, %al /* is byte NUL? */ jz L8 /* yes => return */ incl %ecx /* increment pointer */ /* Now we are aligned. */ jmp L29 /* start copy loop */ ALIGN(4) L28: movl %eax, 12(%ecx,%edx)/* store word at destination */ addl $16, %ecx /* adjust pointer for full round */ L29: 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 L9 /* 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 L9 /* 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 L91 /* 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 L91 /* 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 L92 /* 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 L92 /* 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 L93 /* 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 L28 /* no is NUL => carry on copying */ L93: addl $4, %ecx /* adjust pointer */ L92: addl $4, %ecx L91: addl $4, %ecx L9: movb %al, (%ecx,%edx) /* store first byte of last word */ orb %al, %al /* is it NUL? */ jz L8 /* yes => return */ movb %ah, 1(%ecx,%edx) /* store second byte of last word */ orb %ah, %ah /* is it NUL? */ jz L8 /* 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 L8 /* yes => return */ movb %ah, 3(%ecx,%edx) /* store fourth byte of last word */ L8: movl 8(%esp), %eax /* start address of destination is result */ popl %edi /* restore saved register */ ret PSEUDO_END (strcat)