1/* 2 * Copyright (c) 2007 Apple Inc. All rights reserved. 3 * 4 * @APPLE_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. Please obtain a copy of the License at 10 * http://www.opensource.apple.com/apsl/ and read it before using this 11 * file. 12 * 13 * The Original Code and all software distributed under the License are 14 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER 15 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, 16 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 17 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. 18 * Please see the License for the specific language governing rights and 19 * limitations under the License. 20 * 21 * @APPLE_LICENSE_HEADER_END@ 22 */ 23 24 25// ***************** 26// * S T R L C P Y * 27// ***************** 28// 29// size_t strlcpy(char *dst, const char *src, size_t size); 30// 31// We optimize the move by doing it word parallel. This introduces 32// a complication: if we blindly did word load/stores until finding 33// a 0, we might get a spurious page fault by touching bytes past it. 34// To avoid this, we never do a load that crosses a page boundary, 35// or store unnecessary bytes. 36// 37// The test for 0s relies on the following inobvious but very efficient 38// word-parallel test: 39// x = dataWord + 0xFEFEFEFF 40// y = ~dataWord & 0x80808080 41// if (x & y) == 0 then no zero found 42// The test maps any non-zero byte to zero, and any zero byte to 0x80, 43// with one exception: 0x01 bytes preceeding the first zero are also 44// mapped to 0x80. 45// 46// On Core2 class machines, this word-parallel implementation seems to 47// be slightly faster than using SSE up to about 100 bytes. 48// It is faster than the naive byte-by-byte implementation for 49// operands longer than about 8 bytes. 50 51 .text 52 .globl _strlcpy 53 54 .align 4 55_strlcpy: // size_t *strlcpy(char *dst, const char *src, size_t size); 56 pushl %edi 57 pushl %esi 58 pushl %ebx 59 movl 16(%esp),%edi // get dest ptr 60 movl 20(%esp),%esi // get source ptr 61 movl 24(%esp),%ecx // get length of buffer 62 movl %esi,%edx // copy source ptr 63 negl %edx 64 andl $3,%edx // how many bytes to align source ptr? 65 jz LAligned // already aligned 66 67 68// Loop over bytes. 69// %edi = dest ptr 70// %esi = source ptr 71// %ecx = length remaining in buffer 72// %edx = number of bytes to copy (>0, may not fit in buffer) 73 74LLoopOverBytes: 75 movzb (%esi),%eax // get source byte before checking buffer length 76 testl %ecx,%ecx // buffer full? 77 jz L0NotFound // yes 78 inc %esi 79 dec %ecx 80 movb %al,(%edi) // pack into dest 81 inc %edi 82 testl %eax,%eax // 0? 83 jz LDone // yes, done 84 dec %edx // more to go? 85 jnz LLoopOverBytes 86 87 88// Source is aligned. Loop over words until end of buffer. We 89// align the source, rather than the dest, to avoid getting spurious page faults. 90// %edi = dest ptr (unaligned) 91// %esi = source ptr (word aligned) 92// %ecx = length remaining in buffer 93 94LAligned: 95 movl $5,%edx // if buffer almost exhausted, prepare to copy rest byte-by-byte 96 cmpl $4,%ecx // enough for at least one word? 97 jb LLoopOverBytes 98 99 100// Loop over words. 101// %edi = dest ptr (unaligned) 102// %esi = source ptr (word aligned) 103// %ecx = length remaining in buffer (>=4) 104 105LLoopOverWords: 106 movl (%esi),%eax // get next 4 bytes of source 107 subl $4,%ecx 108 addl $4,%esi 109 movl %eax,%edx // make 2 copies of word 110 movl %eax,%ebx 111 notl %edx // use magic word-parallel test for 0s 112 addl $0xFEFEFEFF,%ebx 113 andl $0x80808080,%edx 114 testl %ebx,%edx 115 jnz L0Found // one of the bytes of %eax is a 0 116 movl %eax,(%edi) // pack 4 bytes into destination 117 addl $4,%edi 118 cmpl $4,%ecx // room in buffer for another word? 119 jae LLoopOverWords // yes 120 121 movl %ecx,%edx // copy leftovers in byte loop 122 jmp LLoopOverBytes 123 124// Found a 0-byte in the word of source. Store a byte at a time until the 0. 125// %edi = dest ptr (unaligned) 126// %eax = last word of source, known to have a 0-byte 127 128LNextByte: 129 shrl $8,%eax // next byte 130L0Found: 131 movb %al,(%edi) // pack in next byte 132 incl %edi 133 testb %al,%al // 0? 134 jnz LNextByte 135 136// Done storing string. 137// %edi = ptr to byte after 0-byte 138 139LDone: 140 subl 16(%esp),%edi // subtract original dest ptr to get length stored 141 decl %edi // don't count the 0-byte 142 movl %edi,%eax // copy to return value 143LExit: 144 popl %ebx 145 popl %esi 146 popl %edi 147 ret 148 149// Buffer filled but 0-byte not found. We return the length of the source string. 150// This is not optimized, as it is an error condition. 151// %edi = dest ptr (ie, 1 past end of buffer) 152// %esi = source ptr (ptr to 1st byte that does not fit) 153 154L0NotFound: 155 movl 24(%esp),%eax // reload buffer length 156 testl %eax,%eax // null? 157 jz 1f // yes, cannot store a 0 158 xorl %edx,%edx // get a 0 159 movb %dl,-1(%edi) // store a 0 at end of buffer to delimit string 1601: 161 movzb (%esi),%edx // get next byte of source 162 incl %esi 163 incl %eax 164 testl %edx,%edx // 0? 165 jnz 1b 166 decl %eax // don't count the 0-byte 167 jmp LExit 168