| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame^] | 1 | /* Compare two memory blocks for differences in the first COUNT bytes. |
| 2 | Copyright (C) 1995-2015 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | |
| 5 | The GNU C Library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public |
| 7 | License as published by the Free Software Foundation; either |
| 8 | version 2.1 of the License, or (at your option) any later version. |
| 9 | |
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 13 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with the GNU C Library; if not, see |
| 17 | <http://www.gnu.org/licenses/>. */ |
| 18 | |
| 19 | #include <sysdep.h> |
| 20 | #include "asm-syntax.h" |
| 21 | |
| 22 | #define PARMS 4+4 /* space for 1 saved reg */ |
| 23 | #define BLK1 PARMS |
| 24 | #define BLK2 BLK1+4 |
| 25 | #define LEN BLK2+4 |
| 26 | |
| 27 | .text |
| 28 | ENTRY (memcmp) |
| 29 | |
| 30 | pushl %esi /* Save callee-safe registers. */ |
| 31 | cfi_adjust_cfa_offset (4) |
| 32 | movl %edi, %edx /* Note that %edx is not used and can |
| 33 | so be used to save %edi. It's faster. */ |
| 34 | cfi_register (edi, edx) |
| 35 | |
| 36 | movl BLK1(%esp), %esi |
| 37 | cfi_rel_offset (esi, 0) |
| 38 | movl BLK2(%esp), %edi |
| 39 | movl LEN(%esp), %ecx |
| 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 L(1) /* 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 latter |
| 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 | L(1): popl %esi /* Restore registers. */ |
| 63 | cfi_adjust_cfa_offset (-4) |
| 64 | cfi_restore (esi) |
| 65 | movl %edx, %edi |
| 66 | cfi_restore (edi) |
| 67 | |
| 68 | ret |
| 69 | END (memcmp) |
| 70 | |
| 71 | #undef bcmp |
| 72 | weak_alias (memcmp, bcmp) |
| 73 | libc_hidden_builtin_def (memcmp) |