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Diffstat (limited to 'sysdeps/i386/strchr.S')
| -rw-r--r-- | sysdeps/i386/strchr.S | 290 |
1 files changed, 0 insertions, 290 deletions
diff --git a/sysdeps/i386/strchr.S b/sysdeps/i386/strchr.S deleted file mode 100644 index 6075e77882..0000000000 --- a/sysdeps/i386/strchr.S +++ /dev/null @@ -1,290 +0,0 @@ -/* strchr (str, ch) -- Return pointer to first occurrence of CH in STR. - For Intel 80x86, x>=3. - Copyright (C) 1994-2017 Free Software Foundation, Inc. - This file is part of the GNU C Library. - Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu> - Some optimisations 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 STR RTN -#define CHR STR+4 - - .text -ENTRY (strchr) - - pushl %edi /* Save callee-safe registers used here. */ - cfi_adjust_cfa_offset (4) - cfi_rel_offset (edi, 0) - movl STR(%esp), %eax - movl CHR(%esp), %edx - - /* At the moment %edx contains C. What we need for the - algorithm is C in all bytes of the dword. Avoid - operations on 16 bit words because these require an - prefix byte (and one more cycle). */ - movb %dl, %dh /* now it is 0|0|c|c */ - movl %edx, %ecx - shll $16, %edx /* now it is c|c|0|0 */ - movw %cx, %dx /* and finally c|c|c|c */ - - /* Before we start with the main loop we process single bytes - until the source pointer is aligned. This has two reasons: - 1. aligned 32-bit memory access is faster - and (more important) - 2. we process in the main loop 32 bit in one step although - we don't know the end of the string. But accessing at - 4-byte alignment guarantees that we never access illegal - memory if this would not also be done by the trivial - implementation (this is because all processor inherent - boundaries are multiples of 4. */ - - testb $3, %al /* correctly aligned ? */ - jz L(11) /* yes => begin loop */ - movb (%eax), %cl /* load byte in question (we need it twice) */ - cmpb %cl, %dl /* compare byte */ - je L(6) /* target found => return */ - testb %cl, %cl /* is NUL? */ - jz L(2) /* yes => return NULL */ - incl %eax /* increment pointer */ - - testb $3, %al /* correctly aligned ? */ - jz L(11) /* yes => begin loop */ - movb (%eax), %cl /* load byte in question (we need it twice) */ - cmpb %cl, %dl /* compare byte */ - je L(6) /* target found => return */ - testb %cl, %cl /* is NUL? */ - jz L(2) /* yes => return NULL */ - incl %eax /* increment pointer */ - - testb $3, %al /* correctly aligned ? */ - jz L(11) /* yes => begin loop */ - movb (%eax), %cl /* load byte in question (we need it twice) */ - cmpb %cl, %dl /* compare byte */ - je L(6) /* target found => return */ - testb %cl, %cl /* is NUL? */ - jz L(2) /* yes => return NULL */ - incl %eax /* increment pointer */ - - /* No we have reached alignment. */ - jmp L(11) /* begin loop */ - - /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to - change any of the hole bits of LONGWORD. - - 1) Is this safe? Will it catch all the zero bytes? - Suppose there is a byte with all zeros. Any carry bits - propagating from its left will fall into the hole at its - least significant bit and stop. Since there will be no - carry from its most significant bit, the LSB of the - byte to the left will be unchanged, and the zero will be - detected. - - 2) Is this worthwhile? Will it ignore everything except - zero bytes? Suppose every byte of LONGWORD has a bit set - somewhere. There will be a carry into bit 8. If bit 8 - is set, this will carry into bit 16. If bit 8 is clear, - one of bits 9-15 must be set, so there will be a carry - into bit 16. Similarly, there will be a carry into bit - 24. If one of bits 24-31 is set, there will be a carry - into bit 32 (=carry flag), so all of the hole bits will - be changed. - - 3) But wait! Aren't we looking for C, not zero? - Good point. So what we do is XOR LONGWORD with a longword, - each of whose bytes is C. This turns each byte that is C - into a zero. */ - - /* Each round the main loop processes 16 bytes. */ - - ALIGN(4) - -L(1): addl $16, %eax /* adjust pointer for whole round */ - -L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */ - xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c - are now 0 */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* C */ - - /* 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(7) - - /* We are only interested in carry bits that change due to the - previous add, so remove original bits */ - xorl %ecx, %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 %edi. */ - jnz L(7) /* found it => return pointer */ - - /* Now we made sure the dword does not contain the character we are - looking for. But because we deal with strings we have to check - for the end of string before testing the next dword. */ - - xorl %edx, %ecx /* restore original dword without reload */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* 0 */ - jnc L(2) /* highest byte is NUL => return NULL */ - xorl %ecx, %edi /* (word+magic)^word */ - 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(2) /* found NUL => return NULL */ - - movl 4(%eax), %ecx /* get word (= 4 bytes) in question */ - xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c - are now 0 */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* C */ - jnc L(71) /* highest byte is C => return pointer */ - xorl %ecx, %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(71) /* found it => return pointer */ - xorl %edx, %ecx /* restore original dword without reload */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* 0 */ - jnc L(2) /* highest byte is NUL => return NULL */ - xorl %ecx, %edi /* (word+magic)^word */ - 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(2) /* found NUL => return NULL */ - - movl 8(%eax), %ecx /* get word (= 4 bytes) in question */ - xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c - are now 0 */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* C */ - jnc L(72) /* highest byte is C => return pointer */ - xorl %ecx, %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(72) /* found it => return pointer */ - xorl %edx, %ecx /* restore original dword without reload */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* 0 */ - jnc L(2) /* highest byte is NUL => return NULL */ - xorl %ecx, %edi /* (word+magic)^word */ - 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(2) /* found NUL => return NULL */ - - movl 12(%eax), %ecx /* get word (= 4 bytes) in question */ - xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c - are now 0 */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* C */ - jnc L(73) /* highest byte is C => return pointer */ - xorl %ecx, %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(73) /* found it => return pointer */ - xorl %edx, %ecx /* restore original dword without reload */ - movl $0xfefefeff, %edi /* magic value */ - addl %ecx, %edi /* add the magic value to the word. We get - carry bits reported for each byte which - is *not* 0 */ - jnc L(2) /* highest byte is NUL => return NULL */ - xorl %ecx, %edi /* (word+magic)^word */ - 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(1) /* no NUL found => restart loop */ - -L(2): /* Return NULL. */ - xorl %eax, %eax - popl %edi /* restore saved register content */ - cfi_adjust_cfa_offset (-4) - cfi_restore (edi) - - ret - - cfi_adjust_cfa_offset (4) - cfi_rel_offset (edi, 0) -L(73): addl $4, %eax /* adjust pointer */ -L(72): addl $4, %eax -L(71): addl $4, %eax - - /* We now scan for the byte in which the character was matched. - But we have to take care of the case that a NUL char is - found before this in the dword. Note that we XORed %ecx - with the byte we're looking for, therefore the tests below look - reversed. */ - -L(7): testb %cl, %cl /* is first byte C? */ - jz L(6) /* yes => return pointer */ - cmpb %dl, %cl /* is first byte NUL? */ - je L(2) /* yes => return NULL */ - incl %eax /* it's not in the first byte */ - - testb %ch, %ch /* is second byte C? */ - jz L(6) /* yes => return pointer */ - cmpb %dl, %ch /* is second byte NUL? */ - je L(2) /* yes => return NULL? */ - incl %eax /* it's not in the second byte */ - - shrl $16, %ecx /* make upper byte accessible */ - testb %cl, %cl /* is third byte C? */ - jz L(6) /* yes => return pointer */ - cmpb %dl, %cl /* is third byte NUL? */ - je L(2) /* yes => return NULL */ - - /* It must be in the fourth byte and it cannot be NUL. */ - incl %eax - -L(6): - popl %edi /* restore saved register content */ - cfi_adjust_cfa_offset (-4) - cfi_restore (edi) - - ret -END (strchr) - -weak_alias (strchr, index) -libc_hidden_builtin_def (strchr) |