1/*
2 * Copyright (c) 2000-2001 Apple Computer, Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
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
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14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
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20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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27 */
28;
29;
30; Strlen, optimized for PPC.  The routine we use is 2-3x faster
31; then the simple loop which checks each byte for zero.
32; For 0- and 1-byte strings, the simple routine is faster, but
33; only by a few cycles.  The algorithm used was adapted from the
34; Mac OS 9 stdCLib strcopy routine, which was originally
35; written by Gary Davidian.  It relies on the following rather
36; inobvious but very efficient test:
37;
38;	y =  dataWord + 0xFEFEFEFF
39;	z = ~dataWord & 0x80808080
40;	if ( y & z ) = 0 then all bytes in dataWord are non-zero
41;
42; The test maps any non-zero byte to zeros and any zero byte to 0x80,
43; with one exception: 0x01 bytes preceeding the first zero are also
44; mapped to 0x80.
45;
46#include <ppc/asm.h>
47#include <ppc/proc_reg.h>
48;
49; int	strlen(ptr)
50;
51;
52
53	.align	5
54	.globl	EXT(strlen)
55LEXT(strlen)
56
57	andi.	r4,r3,0x03		; test alignment first
58	mr	r9,r3			; store the original address for later use....
59	bne	LalignSource		; align the source addr if not already aligned
60Llentry:
61	lis	r5,hi16(0xFEFEFEFF)
62	lis	r6,hi16(0x80808080)
63	subi	r3,r3,0x04		; pre-decrement r3 for the lwzu
64	ori	r5,r5,lo16(0xFEFEFEFF)	; r5=0xFEFEFEFF
65	ori	r6,r6,lo16(0x80808080)	; r6=0x80808080
66
67LLoop:
68	lwzu	r8,4(r3)		; get the first 4 bytes and increment address
69	add	r4,r5,r8		; r4= data + 0xFEFEFEFF
70	andc	r7,r6,r8		; r7= ~data & 0x80808080
71	and.	r4,r4,r7		; r4= r4 & r7
72	beq	LLoop			; if r4 is zero, then all bytes are non-zero
73
74; Now we know one of the bytes in r8 is zero,
75; we just have to figure out which one.
76; We have mapped 0 bytes to 0x80, and nonzero bytes to 0x00,
77; with one exception:
78; 0x01 bytes preceeding the first zero are also mapped to 0x80.
79; So we have to mask out the 0x80s caused by 0x01s before
80; counting leading zeroes to get the bytes in last word.
81
82	rlwinm	r5,r8,7,0,31		; move 0x01 bits to 0x80 position
83	subf	r3,r9,r3		; start to compute string length
84	andc	r4,r4,r5		; turn off false hits from 0x0100 worst case
85	cntlzw	r7,r4			; now we can count leading 0s
86	srwi	r7,r7,3			; convert 0,8,16,24 to 0,1,2,3
87	add	r3,r3,r7		; add in nonzero bytes in last word
88	blr
89
90; We must align the source address for two reasons: to avoid spurious page
91; faults, and for speed.
92;	r4 = low 2 bits of address (1,2, or 3)
93;	r3 = address
94;	r9 = original address (still same as r3)
95
96LalignSource:
97	lbz	r5,0(r3)		; get the first byte...
98	subic.	r4,r4,2			; test for 1, 2 or 3 bytes
99	addi	r3,r3,1			; increment address
100	addi	r6,r9,1			; now r6==r3
101	cmpwi	cr1,r5,0		; zero?
102	beq	cr1,Lreturn		; if its zero return zero
103	bgt	Llentry			; address is aligned now if low bits were 3
104
105	lbz	r5,0(r3)		; get the next byte...
106	addi	r3,r3,1			; increment address
107	cmpwi	cr1,r5,0		; zero?
108	beq	cr1,Lreturn		; if its zero return one
109	beq	Llentry			; addr is aligned now if low bits were 2
110
111	lbz	r5,0(r3)		; get the next byte...
112	addi	r3,r3,1			; increment address
113	cmpwi	cr1,r5,0		; zero?
114	bne	cr1,Llentry		; not zero, continue check (now aligned)
115Lreturn:
116	sub	r3,r3,r6		; get string length (0, 1, or 2)
117	blr
118
119