projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 8f5ca04b RM |
1 | /* memcmp -- compare two memory blocks for differences in the first COUNT |
| 2 | bytes. | |
| 92777700 | 3 | Copyright (C) 1995, 1996 Free Software Foundation, Inc. |
| 8f5ca04b RM |
4 | This file is part of the GNU C Library. |
| 5 | ||
| 6 | The GNU C Library is free software; you can redistribute it and/or | |
| 7 | modify it under the terms of the GNU Library General Public License as | |
| 8 | published by the Free Software Foundation; either version 2 of the | |
| 9 | License, or (at your option) any later version. | |
| 10 | ||
| 11 | The GNU C Library is distributed in the hope that it will be useful, | |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 14 | Library General Public License for more details. | |
| 15 | ||
| 16 | You should have received a copy of the GNU Library General Public | |
| 17 | License along with the GNU C Library; see the file COPYING.LIB. If | |
| 18 | not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, | |
| 19 | Boston, MA 02111-1307, USA. */ | |
| 20 | ||
| 21 | #include <sysdep.h> | |
| 22 | #include "asm-syntax.h" | |
| 23 | ||
| 24 | /* | |
| 25 | INPUT PARAMETERS: | |
| 26 | block1 (sp + 4) | |
| 27 | block2 (sp + 8) | |
| 28 | len (sp + 12) | |
| 29 | */ | |
| 30 | ||
| 31 | .text | |
| 32 | ENTRY (memcmp) | |
| 33 | pushl %esi /* Save callee-safe registers. */ | |
| 34 | movl %edi, %edx /* Note that %edx is not used and can | |
| 35 | so be used to save %edi. It's faster. */ | |
| 36 | ||
| 92777700 RM |
37 | movl 8(%esp), %esi /* Load address of block #1. */ |
| 38 | movl 12(%esp), %edi /* Load address of block #2. */ | |
| 39 | movl 16(%esp), %ecx /* Load maximal length of compare area. */ | |
| 8f5ca04b RM |
40 | |
| 41 | cld /* Set direction of comparison. */ | |
| 42 | ||
| 43 | xorl %eax, %eax /* Default result. */ | |
| 44 | ||
| 45 | repe /* Compare at most %ecx bytes. */ | |
| 46 | cmpsb | |
| 47 | jz L1 /* If even last byte was equal we return 0. */ | |
| 48 | ||
| 49 | /* The memory blocks are not equal. So result of the last | |
| 50 | subtraction is present in the carry flag. It is set when | |
| 51 | the byte in block #2 is bigger. In this case we have to | |
| 52 | return -1 (=0xffffffff), else 1. */ | |
| 53 | sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set | |
| 54 | or not depending on last subtraction. */ | |
| 55 | ||
| 56 | /* At this point %eax == 0, if the byte of block #1 was bigger, and | |
| 57 | 0xffffffff if the last byte of block #2 was bigger. The later | |
| 58 | case is already correct but the former needs a little adjustment. | |
| 59 | Note that the following operation does not change 0xffffffff. */ | |
| 60 | orb $1, %al /* Change 0 to 1. */ | |
| 61 | ||
| 62 | L1: popl %esi /* Restore registers. */ | |
| 63 | movl %edx, %edi | |
| 64 | ||
| 65 | ret | |
| 6ed0492f | 66 | END (memcmp) |
| 8f5ca04b RM |
67 | |
| 68 | #undef bcmp | |
| 69 | weak_alias (memcmp, bcmp) |