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

/*
 * 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
Commit	Line	Data
0b4e3aa0 A	1	/*
	2	* Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved.
	3	*
2d21ac55	4	* @APPLE_OSREFERENCE_LICENSE_HEADER_START@
0b4e3aa0	5	*
2d21ac55 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 License
	10	* may not be used to create, or enable the creation or redistribution of,
	11	* unlawful or unlicensed copies of an Apple operating system, or to
	12	* circumvent, violate, or enable the circumvention or violation of, any
	13	* terms of an Apple operating system software license agreement.
8f6c56a5	14	*
2d21ac55 A	15	* Please obtain a copy of the License at
	16	* http://www.opensource.apple.com/apsl/ and read it before using this file.
	17	*
	18	* The Original Code and all software distributed under the License are
	19	* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
8f6c56a5 A	20	* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
8f6c56a5 A	21	* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
2d21ac55 A	22	* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
	23	* Please see the License for the specific language governing rights and
	24	* limitations under the License.
8f6c56a5	25	*
2d21ac55	26	* @APPLE_OSREFERENCE_LICENSE_HEADER_END@
0b4e3aa0 A	27	*/
	28	;
	29	#include <ppc/asm.h>
	30	#include <ppc/proc_reg.h>
	31	;
	32	; int memcmp(const void LHS, const void RHS, size_t len);
	33	;
	34	; Memcmp returns the difference between the first two different bytes,
	35	; or 0 if the two strings are equal. Because we compare a word at a
	36	; time, this requires a little additional processing once we find a
	37	; difference.
	38	; r3 - LHS
	39	; r4 - RHS
	40	; r5 - len
	41
	42	.align 5
	43	.globl EXT(memcmp)
	44	LEXT(memcmp)
	45
	46	cmpwi cr1,r5,6 ; six is the most common length
	47	mr r6,r3 ; we want to use r3 for compare result
	48	mr. r3,r5 ; test length for 0
	49	bgt cr1,Llong ; handle long strings
	50	blt cr1,Lshort ; and short strings
	51
	52	; six char strings are special cased because they are the most common
	53	Lsix:
	54	lwz r8,0(r6) ; first 4 bytes of LHS
	55	lwz r7,0(r4) ; and RHS
	56	xor. r3,r8,r7 ; compare first 4
	57	bne Ldifferent ; first 4 differed
	58	lhz r8,4(r6) ; last 2 of LHS
	59	lhz r7,4(r4) ; last 2 of RHS
	60	xor. r3,r8,r7 ; compare last 2
	61	beqlr ; done if equal
	62
	63	; strings differ, so we must compute difference between first two
	64	; differing bytes.
	65	; r8 = LHS bytes
	66	; r7 = RHS bytes
	67	; r3 = r8 xor r7 (r3!=0)
	68	Ldifferent:
	69	cntlzw r9,r3 ; count leading 0s in xor
	70	rlwinm r10,r9,0,0,28 ; mask off low 3 bits, so r10 = 0, 8, 16, or 24
	71	subfic r6,r10,24 ; r6 := (24 - r10)
	72	srw r4,r8,r6 ; r4 = LHS differing byte
	73	srw r5,r7,r6 ; r5 = RHS differing byte
	74	sub r3,r4,r5 ; r3 = difference
	75	blr
	76
	77	; handle long strings
	78	Llong:
	79	srwi r0,r5,2 ; r0 = word length
	80	mtctr r0 ; set up for loop
	81	Llongloop:
	82	lwz r8,0(r6) ; next 4 bytes from LHS
	83	addi r6,r6,4
	84	lwz r7,0(r4) ; next 4 from RHS
	85	addi r4,r4,4
	86	xor. r3,r8,r7 ; compare next 4 bytes
	87	bdnzt+ eq,Llongloop ; loop if ctr!=0 and cr0_eq
	88	bne Ldifferent ; these 4 bytes not equal
	89
	90	andi. r5,r5,3 ; more to go?
91
92	; compare short strings (0-5 bytes long)
93	; r5 = length (0-5)
94	; cr0= set on length
95	; r3 = if r5=0, then r3=0
96	Lshort:
97	beqlr ; 0-length strings are defined to be equal (r3=0)
98	mtctr r5
99	Lshortloop:
100	lbz r8,0(r6) ; get next byte from LHS
101	addi r6,r6,1
102	lbz r7,0(r4) ; and next byte from RHS
103	addi r4,r4,1
104	sub. r3,r8,r7 ; compare
105	bdnzt+ eq,Lshortloop ; lloop if ctr!=0 and cr0_eq
106	blr ; done, r3 set correctly by the subtract