1/* 2 * Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved. 3 * 4 * @APPLE_LICENSE_HEADER_START@ 5 * 6 * The contents of this file constitute Original Code as defined in and 7 * are subject to the Apple Public Source License Version 1.1 (the 8 * "License"). You may not use this file except in compliance with the 9 * License. Please obtain a copy of the License at 10 * http://www.apple.com/publicsource and read it before using this file. 11 * 12 * This Original Code and all software distributed under the License are 13 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER 14 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, 15 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 16 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the 17 * License for the specific language governing rights and limitations 18 * under the License. 19 * 20 * @APPLE_LICENSE_HEADER_END@ 21 */ 22; 23#include <ppc/asm.h> 24#include <ppc/proc_reg.h> 25; 26; int memcmp(const void *LHS, const void *RHS, size_t len); 27; 28; Memcmp returns the difference between the first two different bytes, 29; or 0 if the two strings are equal. Because we compare a word at a 30; time, this requires a little additional processing once we find a 31; difference. 32; r3 - LHS 33; r4 - RHS 34; r5 - len 35 36 .align 5 37 .globl EXT(memcmp) 38LEXT(memcmp) 39 40 cmpwi cr1,r5,6 ; six is the most common length 41 mr r6,r3 ; we want to use r3 for compare result 42 mr. r3,r5 ; test length for 0 43 bgt cr1,Llong ; handle long strings 44 blt cr1,Lshort ; and short strings 45 46 ; six char strings are special cased because they are the most common 47Lsix: 48 lwz r8,0(r6) ; first 4 bytes of LHS 49 lwz r7,0(r4) ; and RHS 50 xor. r3,r8,r7 ; compare first 4 51 bne Ldifferent ; first 4 differed 52 lhz r8,4(r6) ; last 2 of LHS 53 lhz r7,4(r4) ; last 2 of RHS 54 xor. r3,r8,r7 ; compare last 2 55 beqlr ; done if equal 56 57 ; strings differ, so we must compute difference between first two 58 ; differing bytes. 59 ; r8 = LHS bytes 60 ; r7 = RHS bytes 61 ; r3 = r8 xor r7 (r3!=0) 62Ldifferent: 63 cntlzw r9,r3 ; count leading 0s in xor 64 rlwinm r10,r9,0,0,28 ; mask off low 3 bits, so r10 = 0, 8, 16, or 24 65 subfic r6,r10,24 ; r6 := (24 - r10) 66 srw r4,r8,r6 ; r4 = LHS differing byte 67 srw r5,r7,r6 ; r5 = RHS differing byte 68 sub r3,r4,r5 ; r3 = difference 69 blr 70 71 ; handle long strings 72Llong: 73 srwi r0,r5,2 ; r0 = word length 74 mtctr r0 ; set up for loop 75Llongloop: 76 lwz r8,0(r6) ; next 4 bytes from LHS 77 addi r6,r6,4 78 lwz r7,0(r4) ; next 4 from RHS 79 addi r4,r4,4 80 xor. r3,r8,r7 ; compare next 4 bytes 81 bdnzt+ eq,Llongloop ; loop if ctr!=0 and cr0_eq 82 bne Ldifferent ; these 4 bytes not equal 83 84 andi. r5,r5,3 ; more to go? 85 86 ; compare short strings (0-5 bytes long) 87 ; r5 = length (0-5) 88 ; cr0= set on length 89 ; r3 = if r5=0, then r3=0 90Lshort: 91 beqlr ; 0-length strings are defined to be equal (r3=0) 92 mtctr r5 93Lshortloop: 94 lbz r8,0(r6) ; get next byte from LHS 95 addi r6,r6,1 96 lbz r7,0(r4) ; and next byte from RHS 97 addi r4,r4,1 98 sub. r3,r8,r7 ; compare 99 bdnzt+ eq,Lshortloop ; lloop if ctr!=0 and cr0_eq 100 blr ; done, r3 set correctly by the subtract 101