projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 5929563f | 1 | /* Compare two memory blocks for differences in the first COUNT bytes. |
| dff8da6b | 2 | Copyright (C) 1995-2024 Free Software Foundation, Inc. |
| 5929563f | 3 | This file is part of the GNU C Library. |
| 8f5ca04b | 4 | |
| 5929563f | 5 | The GNU C Library is free software; you can redistribute it and/or |
| 41bdb6e2 AJ |
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. | |
| 8f5ca04b | 9 | |
| 5929563f UD |
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 | |
| 41bdb6e2 | 13 | Lesser General Public License for more details. |
| 8f5ca04b | 14 | |
| 41bdb6e2 | 15 | You should have received a copy of the GNU Lesser General Public |
| 59ba27a6 | 16 | License along with the GNU C Library; if not, see |
| 5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
| 8f5ca04b RM |
18 | |
| 19 | #include <sysdep.h> | |
| 20 | #include "asm-syntax.h" | |
| 21 | ||
| 2366713d | 22 | #define PARMS 4+4 /* space for 1 saved reg */ |
| 3f02f778 | 23 | #define BLK1 PARMS |
| 2366713d JM |
24 | #define BLK2 BLK1+4 |
| 25 | #define LEN BLK2+4 | |
| 8f5ca04b RM |
26 | |
| 27 | .text | |
| 2366713d | 28 | ENTRY (memcmp) |
| 3f02f778 | 29 | |
| 8f5ca04b | 30 | pushl %esi /* Save callee-safe registers. */ |
| 1ad9da69 | 31 | cfi_adjust_cfa_offset (4) |
| 8f5ca04b RM |
32 | movl %edi, %edx /* Note that %edx is not used and can |
| 33 | so be used to save %edi. It's faster. */ | |
| 1ad9da69 | 34 | cfi_register (edi, edx) |
| 8f5ca04b | 35 | |
| 3f02f778 | 36 | movl BLK1(%esp), %esi |
| 1ad9da69 | 37 | cfi_rel_offset (esi, 0) |
| 3f02f778 GM |
38 | movl BLK2(%esp), %edi |
| 39 | movl LEN(%esp), %ecx | |
| 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 | |
| 5929563f | 47 | jz L(1) /* If even last byte was equal we return 0. */ |
| 8f5ca04b RM |
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 | |
| 49c091e5 | 57 | 0xffffffff if the last byte of block #2 was bigger. The latter |
| 8f5ca04b RM |
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 | ||
| 92945b52 | 62 | L(1): popl %esi /* Restore registers. */ |
| 1ad9da69 UD |
63 | cfi_adjust_cfa_offset (-4) |
| 64 | cfi_restore (esi) | |
| 8f5ca04b | 65 | movl %edx, %edi |
| 1ad9da69 | 66 | cfi_restore (edi) |
| 8f5ca04b RM |
67 | |
| 68 | ret | |
| 2366713d | 69 | END (memcmp) |
| 8f5ca04b RM |
70 | |
| 71 | #undef bcmp | |
| 2366713d | 72 | weak_alias (memcmp, bcmp) |
| 44829b3d NG |
73 | #undef __memcmpeq |
| 74 | strong_alias (memcmp, __memcmpeq) | |
| 2366713d | 75 | libc_hidden_builtin_def (memcmp) |
| 9894127d | 76 | libc_hidden_def (__memcmpeq) |