1/* 2 * CDDL HEADER START 3 * 4 * The contents of this file are subject to the terms of the 5 * Common Development and Distribution License (the "License"). 6 * You may not use this file except in compliance with the License. 7 * 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9 * or http://www.opensolaris.org/os/licensing. 10 * See the License for the specific language governing permissions 11 * and limitations under the License. 12 * 13 * When distributing Covered Code, include this CDDL HEADER in each 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15 * If applicable, add the following below this CDDL HEADER, with the 16 * fields enclosed by brackets "[]" replaced with your own identifying 17 * information: Portions Copyright [yyyy] [name of copyright owner] 18 * 19 * CDDL HEADER END 20 */ 21/* 22 * Copyright 2004 Sun Microsystems, Inc. All rights reserved. 23 * Use is subject to license terms. 24 */ 25 26 .file "strncpy.s" 27 28/ 29/ strncpy(s1, s2, n) 30/ 31/ Copies s2 to s1, truncating or null-padding to always copy n bytes 32/ Returns s1 33/ 34/ Fast assembly language version of the following C-program strncpy 35/ which represents the `standard' for the C-library. 36/ 37/ char * 38/ strncpy(char *s1, const char *s2, size_t n) 39/ { 40/ char *os1 = s1; 41/ 42/ n++; 43/ while ((--n != 0) && ((*s1++ = *s2++) != '\0')) 44/ ; 45/ if (n != 0) 46/ while (--n != 0) 47/ *s1++ = '\0'; 48/ return (os1); 49/ } 50/ 51/ In this assembly language version, the following expression is used 52/ to check if a 32-bit word data contains a null byte or not: 53/ (((A & 0x7f7f7f7f) + 0x7f7f7f7f) | A) & 0x80808080 54/ If the above expression geneates a value other than 0x80808080, 55/ that means the 32-bit word data contains a null byte. 56/ 57 58/ Assume relatively long strings and small numbers of nulls at end. 59 60#include "SYS.h" 61 62 ENTRY(strncpy) 63 pushl %edi / save register variables 64 pushl %esi 65 66 movl 16(%esp), %eax / %eax = source string address 67 movl 12(%esp), %edi / %edi = destination string address 68 movl 20(%esp), %esi / %esi = number of bytes 69 70 testl $3, %eax / if %eax not word aligned 71 jnz .L1 / goto .L1 72.L8: 73 cmpl $4, %esi / if number of bytes < 4 74 jb .L4 / goto .L4 75 .align 4 76.L2: 77 movl (%eax), %edx / move 1 word from (%eax) to %edx 78 movl $0x7f7f7f7f, %ecx 79 andl %edx, %ecx / %ecx = %edx & 0x7f7f7f7f 80 addl $4, %eax / next word 81 addl $0x7f7f7f7f, %ecx / %ecx += 0x7f7f7f7f 82 orl %edx, %ecx / %ecx |= %edx 83 andl $0x80808080, %ecx / %ecx &= 0x80808080 84 cmpl $0x80808080, %ecx / if null byte in this word 85 jne .L3 / goto .L3 86 movl %edx, (%edi) / copy this word to (%edi) 87 subl $4, %esi / decrement number of bytes by 4 88 addl $4, %edi / next word 89 cmpl $4, %esi / if number of bytes >= 4 90 jae .L2 / goto .L2 91 jmp .L4 / goto .L4 92.L3: 93 subl $4, %eax / post-incremented 94 .align 4 95.L4: 96 / (number of bytes < 4) or (a null byte found in the word) 97 cmpl $0, %esi / if number of bytes == 0 98 je .L7 / goto .L7 (finished) 99 movb (%eax), %dl / %dl = a byte in (%eax) 100 decl %esi / decrement number of bytes by 1 101 movb %dl, (%edi) / copy %dl to (%edi) 102 incl %eax / next byte 103 incl %edi / next byte 104 cmpb $0, %dl / compare %dl with a null byte 105 je .L5 / if %dl is a null, goto .L5 106 jmp .L4 / goto .L4 107 .align 4 108.L1: 109 / %eax not aligned 110 cmpl $0, %esi / if number of bytes == 0 111 je .L7 / goto .L7 (finished) 112 movb (%eax), %dl / %dl = a byte in (%eax) 113 decl %esi / decrement number of bytes by 1 114 movb %dl, (%edi) / copy %dl to (%edi) 115 incl %edi / next byte 116 incl %eax / next byte 117 cmpb $0, %dl / compare %dl with a null byte 118 je .L5 / if %dl is a null, goto .L5 119 testl $3, %eax / if %eax word aligned 120 jz .L8 / goto .L8 121 jmp .L1 / goto .L1 (not word aligned) 122 .align 4 123.L5: 124 movl %esi, %ecx / %ecx = length to copy null bytes 125 xorl %eax, %eax / clear %eax 126 shrl $2, %ecx / %ecx = words to copy null bytes 127 rep ; sstol / rep;sstol is optimal 128 andl $3, %esi / %esi = leftover bytes 129.L6: 130 cmpl $0, %esi / if number of bytes == 0 131 jz .L7 / goto .L7 (finished) 132 movb $0, (%edi) / move a null byte to (%edi) 133 decl %esi / decrement number of bytes by 1 134 incl %edi / next byte 135 jmp .L6 / goto .L6 136 .align 4 137.L7: 138 movl 12(%esp), %eax / return the destination address 139 popl %esi / restore register variables 140 popl %edi 141 ret 142 SET_SIZE(strncpy) 143