[apple/xnu.git] / libkern / ppc / memcmp.s

/*
 * Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_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
Commit	Line	Data
0b4e3aa0 A	1	/*
	2	* Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved.
	3	*
	4	* @APPLE_LICENSE_HEADER_START@
	5	*
37839358 A	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.
0b4e3aa0	11	*
37839358 A	12	* This Original Code and all software distributed under the License are
37839358 A	13	* distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
0b4e3aa0 A	14	* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
0b4e3aa0 A	15	* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
37839358 A	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.
0b4e3aa0 A	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)
	38	LEXT(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
	47	Lsix:
	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)
	62	Ldifferent:
	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
	72	Llong:
	73	srwi r0,r5,2 ; r0 = word length
	74	mtctr r0 ; set up for loop
	75	Llongloop:
	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
90	Lshort:
91	beqlr ; 0-length strings are defined to be equal (r3=0)
92	mtctr r5
93	Lshortloop:
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