| /* Compare two memory blocks for differences in the first COUNT bytes. |
| Copyright (C) 1995-2016 Free Software Foundation, Inc. |
| 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 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 BLK1 PARMS |
| #define BLK2 BLK1+4 |
| #define LEN BLK2+4 |
| |
| .text |
| ENTRY (memcmp) |
| |
| pushl %esi /* Save callee-safe registers. */ |
| cfi_adjust_cfa_offset (4) |
| movl %edi, %edx /* Note that %edx is not used and can |
| so be used to save %edi. It's faster. */ |
| cfi_register (edi, edx) |
| |
| movl BLK1(%esp), %esi |
| cfi_rel_offset (esi, 0) |
| movl BLK2(%esp), %edi |
| movl LEN(%esp), %ecx |
| |
| cld /* Set direction of comparison. */ |
| |
| xorl %eax, %eax /* Default result. */ |
| |
| repe /* Compare at most %ecx bytes. */ |
| cmpsb |
| jz L(1) /* If even last byte was equal we return 0. */ |
| |
| /* The memory blocks are not equal. So result of the last |
| subtraction is present in the carry flag. It is set when |
| the byte in block #2 is bigger. In this case we have to |
| return -1 (=0xffffffff), else 1. */ |
| sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set |
| or not depending on last subtraction. */ |
| |
| /* At this point %eax == 0, if the byte of block #1 was bigger, and |
| 0xffffffff if the last byte of block #2 was bigger. The latter |
| case is already correct but the former needs a little adjustment. |
| Note that the following operation does not change 0xffffffff. */ |
| orb $1, %al /* Change 0 to 1. */ |
| |
| L(1): popl %esi /* Restore registers. */ |
| cfi_adjust_cfa_offset (-4) |
| cfi_restore (esi) |
| movl %edx, %edi |
| cfi_restore (edi) |
| |
| ret |
| END (memcmp) |
| |
| #undef bcmp |
| weak_alias (memcmp, bcmp) |
| libc_hidden_builtin_def (memcmp) |