diff options
Diffstat (limited to 'sysdeps/i386/i586/strlen.S')
| -rw-r--r-- | sysdeps/i386/i586/strlen.S | 182 |
1 files changed, 0 insertions, 182 deletions
diff --git a/sysdeps/i386/i586/strlen.S b/sysdeps/i386/i586/strlen.S deleted file mode 100644 index cfea2e020f..0000000000 --- a/sysdeps/i386/i586/strlen.S +++ /dev/null @@ -1,182 +0,0 @@ -/* strlen -- Compute length of NUL terminated string. - Highly optimized version for ix86, x>=5. - Copyright (C) 1995-2017 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, see - <http://www.gnu.org/licenses/>. */ - -#include <sysdep.h> -#include "asm-syntax.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 4 /* no space for saved regs */ -#define STR PARMS - - .text -ENTRY (strlen) - - movl STR(%esp), %eax - movl $3, %edx /* load mask (= 3) */ - - andl %eax, %edx /* separate last two bits of address */ - - jz L(1) /* aligned => start loop */ - jp L(0) /* exactly two bits set */ - - cmpb %dh, (%eax) /* is byte NUL? */ - je L(2) /* yes => return */ - - incl %eax /* increment pointer */ - cmpb %dh, (%eax) /* is byte NUL? */ - - je L(2) /* yes => return */ - - incl %eax /* increment pointer */ - xorl $2, %edx - - jz L(1) - -L(0): cmpb %dh, (%eax) /* is byte NUL? */ - je L(2) /* yes => return */ - - incl %eax /* increment pointer */ - xorl %edx, %edx /* We need %edx == 0 for later */ - - /* 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. - - Note: %edx == 0 in any case here. */ - -L(1): - movl (%eax), %ecx /* get word (= 4 bytes) in question */ - addl $4, %eax /* adjust pointer for *next* word */ - - subl %ecx, %edx /* first step to negate word */ - addl $magic, %ecx /* add magic word */ - - decl %edx /* complete negation of word */ - jnc L(3) /* previous addl caused overflow? */ - - xorl %ecx, %edx /* (word+magic)^word */ - - andl $~magic, %edx /* any of the carry flags set? */ - - jne L(3) /* yes => determine byte */ - - - movl (%eax), %ecx /* get word (= 4 bytes) in question */ - addl $4, %eax /* adjust pointer for *next* word */ - - subl %ecx, %edx /* first step to negate word */ - addl $magic, %ecx /* add magic word */ - - decl %edx /* complete negation of word */ - jnc L(3) /* previous addl caused overflow? */ - - xorl %ecx, %edx /* (word+magic)^word */ - - andl $~magic, %edx /* any of the carry flags set? */ - - jne L(3) /* yes => determine byte */ - - - movl (%eax), %ecx /* get word (= 4 bytes) in question */ - addl $4, %eax /* adjust pointer for *next* word */ - - subl %ecx, %edx /* first step to negate word */ - addl $magic, %ecx /* add magic word */ - - decl %edx /* complete negation of word */ - jnc L(3) /* previous addl caused overflow? */ - - xorl %ecx, %edx /* (word+magic)^word */ - - andl $~magic, %edx /* any of the carry flags set? */ - - jne L(3) /* yes => determine byte */ - - - movl (%eax), %ecx /* get word (= 4 bytes) in question */ - addl $4, %eax /* adjust pointer for *next* word */ - - subl %ecx, %edx /* first step to negate word */ - addl $magic, %ecx /* add magic word */ - - decl %edx /* complete negation of word */ - jnc L(3) /* previous addl caused overflow? */ - - xorl %ecx, %edx /* (word+magic)^word */ - - andl $~magic, %edx /* any of the carry flags set? */ - - je L(1) /* no => start loop again */ - - -L(3): subl $4, %eax /* correct too early pointer increment */ - subl $magic, %ecx - - cmpb $0, %cl /* lowest byte NUL? */ - jz L(2) /* yes => return */ - - inc %eax /* increment pointer */ - testb %ch, %ch /* second byte NUL? */ - - jz L(2) /* yes => return */ - - shrl $16, %ecx /* make upper bytes accessible */ - incl %eax /* increment pointer */ - - cmpb $0, %cl /* is third byte NUL? */ - jz L(2) /* yes => return */ - - incl %eax /* increment pointer */ - -L(2): subl STR(%esp), %eax /* now compute the length as difference - between start and terminating NUL - character */ - ret -END (strlen) -libc_hidden_builtin_def (strlen) |