projects / apple / xnu.git / blame
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|---|---|---|
| 0b4e3aa0 A |
1 | /* |
| 2 | * Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved. | |
| 3 | * | |
| 8ad349bb | 4 | * @APPLE_LICENSE_OSREFERENCE_HEADER_START@ |
| 0b4e3aa0 | 5 | * |
| 8ad349bb A |
6 | * This file contains Original Code and/or Modifications of Original Code |
| 7 | * as defined in and that are subject to the Apple Public Source License | |
| 8 | * Version 2.0 (the 'License'). You may not use this file except in | |
| 9 | * compliance with the License. The rights granted to you under the | |
| 10 | * License may not be used to create, or enable the creation or | |
| 11 | * redistribution of, unlawful or unlicensed copies of an Apple operating | |
| 12 | * system, or to circumvent, violate, or enable the circumvention or | |
| 13 | * violation of, any terms of an Apple operating system software license | |
| 14 | * agreement. | |
| 15 | * | |
| 16 | * Please obtain a copy of the License at | |
| 17 | * http://www.opensource.apple.com/apsl/ and read it before using this | |
| 18 | * file. | |
| 19 | * | |
| 20 | * The Original Code and all software distributed under the License are | |
| 21 | * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER | |
| 22 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, | |
| 23 | * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, | |
| 24 | * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. | |
| 25 | * Please see the License for the specific language governing rights and | |
| 26 | * limitations under the License. | |
| 27 | * | |
| 28 | * @APPLE_LICENSE_OSREFERENCE_HEADER_END@ | |
| 0b4e3aa0 A |
29 | */ |
| 30 | ; | |
| 31 | #include <ppc/asm.h> | |
| 32 | #include <ppc/proc_reg.h> | |
| 33 | ; | |
| 34 | ; int memcmp(const void *LHS, const void *RHS, size_t len); | |
| 35 | ; | |
| 36 | ; Memcmp returns the difference between the first two different bytes, | |
| 37 | ; or 0 if the two strings are equal. Because we compare a word at a | |
| 38 | ; time, this requires a little additional processing once we find a | |
| 39 | ; difference. | |
| 40 | ; r3 - LHS | |
| 41 | ; r4 - RHS | |
| 42 | ; r5 - len | |
| 43 | ||
| 44 | .align 5 | |
| 45 | .globl EXT(memcmp) | |
| 46 | LEXT(memcmp) | |
| 47 | ||
| 48 | cmpwi cr1,r5,6 ; six is the most common length | |
| 49 | mr r6,r3 ; we want to use r3 for compare result | |
| 50 | mr. r3,r5 ; test length for 0 | |
| 51 | bgt cr1,Llong ; handle long strings | |
| 52 | blt cr1,Lshort ; and short strings | |
| 53 | ||
| 54 | ; six char strings are special cased because they are the most common | |
| 55 | Lsix: | |
| 56 | lwz r8,0(r6) ; first 4 bytes of LHS | |
| 57 | lwz r7,0(r4) ; and RHS | |
| 58 | xor. r3,r8,r7 ; compare first 4 | |
| 59 | bne Ldifferent ; first 4 differed | |
| 60 | lhz r8,4(r6) ; last 2 of LHS | |
| 61 | lhz r7,4(r4) ; last 2 of RHS | |
| 62 | xor. r3,r8,r7 ; compare last 2 | |
| 63 | beqlr ; done if equal | |
| 64 | ||
| 65 | ; strings differ, so we must compute difference between first two | |
| 66 | ; differing bytes. | |
| 67 | ; r8 = LHS bytes | |
| 68 | ; r7 = RHS bytes | |
| 69 | ; r3 = r8 xor r7 (r3!=0) | |
| 70 | Ldifferent: | |
| 71 | cntlzw r9,r3 ; count leading 0s in xor | |
| 72 | rlwinm r10,r9,0,0,28 ; mask off low 3 bits, so r10 = 0, 8, 16, or 24 | |
| 73 | subfic r6,r10,24 ; r6 := (24 - r10) | |
| 74 | srw r4,r8,r6 ; r4 = LHS differing byte | |
| 75 | srw r5,r7,r6 ; r5 = RHS differing byte | |
| 76 | sub r3,r4,r5 ; r3 = difference | |
| 77 | blr | |
| 78 | ||
| 79 | ; handle long strings | |
| 80 | Llong: | |
| 81 | srwi r0,r5,2 ; r0 = word length | |
| 82 | mtctr r0 ; set up for loop | |
| 83 | Llongloop: | |
| 84 | lwz r8,0(r6) ; next 4 bytes from LHS | |
| 85 | addi r6,r6,4 | |
| 86 | lwz r7,0(r4) ; next 4 from RHS | |
| 87 | addi r4,r4,4 | |
| 88 | xor. r3,r8,r7 ; compare next 4 bytes | |
| 89 | bdnzt+ eq,Llongloop ; loop if ctr!=0 and cr0_eq | |
| 90 | bne Ldifferent ; these 4 bytes not equal | |
| 91 | ||
| 92 | andi. r5,r5,3 ; more to go? | |
| 93 | ||
| 94 | ; compare short strings (0-5 bytes long) | |
| 95 | ; r5 = length (0-5) | |
| 96 | ; cr0= set on length | |
| 97 | ; r3 = if r5=0, then r3=0 | |
| 98 | Lshort: | |
| 99 | beqlr ; 0-length strings are defined to be equal (r3=0) | |
| 100 | mtctr r5 | |
| 101 | Lshortloop: | |
| 102 | lbz r8,0(r6) ; get next byte from LHS | |
| 103 | addi r6,r6,1 | |
| 104 | lbz r7,0(r4) ; and next byte from RHS | |
| 105 | addi r4,r4,1 | |
| 106 | sub. r3,r8,r7 ; compare | |
| 107 | bdnzt+ eq,Lshortloop ; lloop if ctr!=0 and cr0_eq | |
| 108 | blr ; done, r3 set correctly by the subtract |