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 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. 14 * 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 20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, 21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 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. 25 * 26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ 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