/* * Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved. * * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. The rights granted to you under the License * may not be used to create, or enable the creation or redistribution of, * unlawful or unlicensed copies of an Apple operating system, or to * circumvent, violate, or enable the circumvention or violation of, any * terms of an Apple operating system software license agreement. * * Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ */ ; #include <ppc/asm.h> #include <ppc/proc_reg.h> ; ; int memcmp(const void *LHS, const void *RHS, size_t len); ; ; Memcmp returns the difference between the first two different bytes, ; or 0 if the two strings are equal. Because we compare a word at a ; time, this requires a little additional processing once we find a ; difference. ; r3 - LHS ; r4 - RHS ; r5 - len .align 5 .globl EXT(memcmp) LEXT(memcmp) cmpwi cr1,r5,6 ; six is the most common length mr r6,r3 ; we want to use r3 for compare result mr. r3,r5 ; test length for 0 bgt cr1,Llong ; handle long strings blt cr1,Lshort ; and short strings ; six char strings are special cased because they are the most common Lsix: lwz r8,0(r6) ; first 4 bytes of LHS lwz r7,0(r4) ; and RHS xor. r3,r8,r7 ; compare first 4 bne Ldifferent ; first 4 differed lhz r8,4(r6) ; last 2 of LHS lhz r7,4(r4) ; last 2 of RHS xor. r3,r8,r7 ; compare last 2 beqlr ; done if equal ; strings differ, so we must compute difference between first two ; differing bytes. ; r8 = LHS bytes ; r7 = RHS bytes ; r3 = r8 xor r7 (r3!=0) Ldifferent: cntlzw r9,r3 ; count leading 0s in xor rlwinm r10,r9,0,0,28 ; mask off low 3 bits, so r10 = 0, 8, 16, or 24 subfic r6,r10,24 ; r6 := (24 - r10) srw r4,r8,r6 ; r4 = LHS differing byte srw r5,r7,r6 ; r5 = RHS differing byte sub r3,r4,r5 ; r3 = difference blr ; handle long strings Llong: srwi r0,r5,2 ; r0 = word length mtctr r0 ; set up for loop Llongloop: lwz r8,0(r6) ; next 4 bytes from LHS addi r6,r6,4 lwz r7,0(r4) ; next 4 from RHS addi r4,r4,4 xor. r3,r8,r7 ; compare next 4 bytes bdnzt+ eq,Llongloop ; loop if ctr!=0 and cr0_eq bne Ldifferent ; these 4 bytes not equal andi. r5,r5,3 ; more to go? ; compare short strings (0-5 bytes long) ; r5 = length (0-5) ; cr0= set on length ; r3 = if r5=0, then r3=0 Lshort: beqlr ; 0-length strings are defined to be equal (r3=0) mtctr r5 Lshortloop: lbz r8,0(r6) ; get next byte from LHS addi r6,r6,1 lbz r7,0(r4) ; and next byte from RHS addi r4,r4,1 sub. r3,r8,r7 ; compare bdnzt+ eq,Lshortloop ; lloop if ctr!=0 and cr0_eq blr ; done, r3 set correctly by the subtract