| /* Find character CH in a NUL terminated string. |
| Highly optimized version for ix85, x>=5. |
| Copyright (C) 1995,1996,1997,2000,2003,2005 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Ulrich Drepper, <drepper@gnu.ai.mit.edu>. |
| |
| 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, write to the Free |
| Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. */ |
| |
| #include <sysdep.h> |
| #include "asm-syntax.h" |
| #include "bp-sym.h" |
| #include "bp-asm.h" |
| |
| /* This version is especially optimized for the i586 (and following?) |
| processors. This is mainly done by using the two pipelines. The |
| version optimized for i486 is weak in this aspect because to get |
| as much parallelism we have to execute some *more* instructions. |
| |
| The code below is structured to reflect the pairing of the instructions |
| as *I think* it is. I have no processor data book to verify this. |
| If you find something you think is incorrect let me know. */ |
| |
| |
| /* The magic value which is used throughout in the whole code. */ |
| #define magic 0xfefefeff |
| |
| #define PARMS LINKAGE+16 /* space for 4 saved regs */ |
| #define RTN PARMS |
| #define STR RTN+RTN_SIZE |
| #define CHR STR+PTR_SIZE |
| |
| .text |
| ENTRY (BP_SYM (strchr)) |
| ENTER |
| |
| pushl %edi /* Save callee-safe registers. */ |
| cfi_adjust_cfa_offset (-4) |
| pushl %esi |
| cfi_adjust_cfa_offset (-4) |
| |
| pushl %ebx |
| cfi_adjust_cfa_offset (-4) |
| pushl %ebp |
| cfi_adjust_cfa_offset (-4) |
| |
| movl STR(%esp), %eax |
| movl CHR(%esp), %edx |
| CHECK_BOUNDS_LOW (%eax, STR(%esp)) |
| |
| movl %eax, %edi /* duplicate string pointer for later */ |
| cfi_rel_offset (edi, 12) |
| xorl %ecx, %ecx /* clear %ecx */ |
| |
| /* 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 */ |
| movb %dl, %cl /* we construct the lower half in %ecx */ |
| |
| shll $16, %edx /* now %edx is c|c|0|0 */ |
| movb %cl, %ch /* now %ecx is 0|0|c|c */ |
| |
| orl %ecx, %edx /* and finally c|c|c|c */ |
| andl $3, %edi /* mask alignment bits */ |
| |
| jz L(11) /* alignment is 0 => start loop */ |
| |
| movb %dl, %cl /* 0 is needed below */ |
| jp L(0) /* exactly two bits set */ |
| |
| xorb (%eax), %cl /* is byte the one we are looking for? */ |
| jz L(2) /* yes => return pointer */ |
| |
| xorb %dl, %cl /* load single byte and test for NUL */ |
| je L(3) /* yes => return NULL */ |
| |
| movb 1(%eax), %cl /* load single byte */ |
| incl %eax |
| |
| cmpb %cl, %dl /* is byte == C? */ |
| je L(2) /* aligned => return pointer */ |
| |
| cmpb $0, %cl /* is byte NUL? */ |
| je L(3) /* yes => return NULL */ |
| |
| incl %eax |
| decl %edi |
| |
| jne L(11) |
| |
| L(0): movb (%eax), %cl /* load single byte */ |
| |
| cmpb %cl, %dl /* is byte == C? */ |
| je L(2) /* aligned => return pointer */ |
| |
| cmpb $0, %cl /* is byte NUL? */ |
| je L(3) /* yes => return NULL */ |
| |
| incl %eax /* increment pointer */ |
| |
| cfi_rel_offset (esi, 8) |
| cfi_rel_offset (ebx, 4) |
| cfi_rel_offset (ebp, 0) |
| |
| /* The following code is the preparation for the loop. The |
| four instruction up to `L1' will not be executed in the loop |
| because the same code is found at the end of the loop, but |
| there it is executed in parallel with other instructions. */ |
| L(11): movl (%eax), %ecx |
| movl $magic, %ebp |
| |
| movl $magic, %edi |
| addl %ecx, %ebp |
| |
| /* The main loop: it looks complex and indeed it is. I would |
| love to say `it was hard to write, so it should he hard to |
| read' but I will give some more hints. To fully understand |
| this code you should first take a look at the i486 version. |
| The basic algorithm is the same, but here the code organized |
| in a way which permits to use both pipelines all the time. |
| |
| I tried to make it a bit more understandable by indenting |
| the code according to stage in the algorithm. It goes as |
| follows: |
| check for 0 in 1st word |
| check for C in 1st word |
| check for 0 in 2nd word |
| check for C in 2nd word |
| check for 0 in 3rd word |
| check for C in 3rd word |
| check for 0 in 4th word |
| check for C in 4th word |
| |
| Please note that doing the test for NUL before the test for |
| C allows us to overlap the test for 0 in the next word with |
| the test for C. */ |
| |
| L(1): xorl %ecx, %ebp /* (word^magic) */ |
| addl %ecx, %edi /* add magic word */ |
| |
| leal 4(%eax), %eax /* increment pointer */ |
| jnc L(4) /* previous addl caused overflow? */ |
| |
| movl %ecx, %ebx /* duplicate original word */ |
| orl $magic, %ebp /* (word^magic)|magic */ |
| |
| addl $1, %ebp /* (word^magic)|magic == 0xffffffff? */ |
| jne L(4) /* yes => we found word with NUL */ |
| |
| movl $magic, %esi /* load magic value */ |
| xorl %edx, %ebx /* clear words which are C */ |
| |
| movl (%eax), %ecx |
| addl %ebx, %esi /* (word+magic) */ |
| |
| movl $magic, %edi |
| jnc L(5) /* previous addl caused overflow? */ |
| |
| movl %edi, %ebp |
| xorl %ebx, %esi /* (word+magic)^word */ |
| |
| addl %ecx, %ebp |
| orl $magic, %esi /* ((word+magic)^word)|magic */ |
| |
| addl $1, %esi /* ((word+magic)^word)|magic==0xf..f?*/ |
| jne L(5) /* yes => we found word with C */ |
| |
| xorl %ecx, %ebp |
| addl %ecx, %edi |
| |
| leal 4(%eax), %eax |
| jnc L(4) |
| |
| movl %ecx, %ebx |
| orl $magic, %ebp |
| |
| addl $1, %ebp |
| jne L(4) |
| |
| movl $magic, %esi |
| xorl %edx, %ebx |
| |
| movl (%eax), %ecx |
| addl %ebx, %esi |
| |
| movl $magic, %edi |
| jnc L(5) |
| |
| movl %edi, %ebp |
| xorl %ebx, %esi |
| |
| addl %ecx, %ebp |
| orl $magic, %esi |
| |
| addl $1, %esi |
| jne L(5) |
| |
| xorl %ecx, %ebp |
| addl %ecx, %edi |
| |
| leal 4(%eax), %eax |
| jnc L(4) |
| |
| movl %ecx, %ebx |
| orl $magic, %ebp |
| |
| addl $1, %ebp |
| jne L(4) |
| |
| movl $magic, %esi |
| xorl %edx, %ebx |
| |
| movl (%eax), %ecx |
| addl %ebx, %esi |
| |
| movl $magic, %edi |
| jnc L(5) |
| |
| movl %edi, %ebp |
| xorl %ebx, %esi |
| |
| addl %ecx, %ebp |
| orl $magic, %esi |
| |
| addl $1, %esi |
| jne L(5) |
| |
| xorl %ecx, %ebp |
| addl %ecx, %edi |
| |
| leal 4(%eax), %eax |
| jnc L(4) |
| |
| movl %ecx, %ebx |
| orl $magic, %ebp |
| |
| addl $1, %ebp |
| jne L(4) |
| |
| movl $magic, %esi |
| xorl %edx, %ebx |
| |
| movl (%eax), %ecx |
| addl %ebx, %esi |
| |
| movl $magic, %edi |
| jnc L(5) |
| |
| movl %edi, %ebp |
| xorl %ebx, %esi |
| |
| addl %ecx, %ebp |
| orl $magic, %esi |
| |
| addl $1, %esi |
| |
| je L(1) |
| |
| /* We know there is no NUL byte but a C byte in the word. |
| %ebx contains NUL in this particular byte. */ |
| L(5): subl $4, %eax /* adjust pointer */ |
| testb %bl, %bl /* first byte == C? */ |
| |
| jz L(2) /* yes => return pointer */ |
| |
| incl %eax /* increment pointer */ |
| testb %bh, %bh /* second byte == C? */ |
| |
| jz L(2) /* yes => return pointer */ |
| |
| shrl $16, %ebx /* make upper bytes accessible */ |
| incl %eax /* increment pointer */ |
| |
| cmp $0, %bl /* third byte == C */ |
| je L(2) /* yes => return pointer */ |
| |
| incl %eax /* increment pointer */ |
| |
| L(2): CHECK_BOUNDS_HIGH (%eax, STR(%esp), jb) |
| RETURN_BOUNDED_POINTER (STR(%esp)) |
| L(out): popl %ebp /* restore saved registers */ |
| cfi_adjust_cfa_offset (-4) |
| cfi_restore (ebp) |
| popl %ebx |
| cfi_adjust_cfa_offset (-4) |
| cfi_restore (ebx) |
| |
| popl %esi |
| cfi_adjust_cfa_offset (-4) |
| cfi_restore (esi) |
| popl %edi |
| cfi_adjust_cfa_offset (-4) |
| cfi_restore (edi) |
| |
| LEAVE |
| RET_PTR |
| |
| cfi_adjust_cfa_offset (16) |
| cfi_rel_offset (edi, 12) |
| cfi_rel_offset (esi, 8) |
| cfi_rel_offset (ebx, 4) |
| cfi_rel_offset (ebp, 0) |
| /* We know there is a NUL byte in the word. But we have to test |
| whether there is an C byte before it in the word. */ |
| L(4): subl $4, %eax /* adjust pointer */ |
| cmpb %dl, %cl /* first byte == C? */ |
| |
| je L(2) /* yes => return pointer */ |
| |
| cmpb $0, %cl /* first byte == NUL? */ |
| je L(3) /* yes => return NULL */ |
| |
| incl %eax /* increment pointer */ |
| |
| cmpb %dl, %ch /* second byte == C? */ |
| je L(2) /* yes => return pointer */ |
| |
| cmpb $0, %ch /* second byte == NUL? */ |
| je L(3) /* yes => return NULL */ |
| |
| shrl $16, %ecx /* make upper bytes accessible */ |
| incl %eax /* increment pointer */ |
| |
| cmpb %dl, %cl /* third byte == C? */ |
| je L(2) /* yes => return pointer */ |
| |
| cmpb $0, %cl /* third byte == NUL? */ |
| je L(3) /* yes => return NULL */ |
| |
| incl %eax /* increment pointer */ |
| |
| /* The test four the fourth byte is necessary! */ |
| cmpb %dl, %ch /* fourth byte == C? */ |
| je L(2) /* yes => return pointer */ |
| |
| L(3): xorl %eax, %eax |
| RETURN_NULL_BOUNDED_POINTER |
| jmp L(out) |
| END (BP_SYM (strchr)) |
| |
| #undef index |
| weak_alias (BP_SYM (strchr), BP_SYM (index)) |
| libc_hidden_builtin_def (strchr) |
