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 "strncat.s" 27 28/ 29/ strncat(s1, s2, n) 30/ 31/ Concatenates s2 on the end of s1. s1's space must be large enough. 32/ At most n characters are moved. 33/ Returns s1. 34/ 35/ Fast assembly language version of the following C-program strncat 36/ which represents the `standard' for the C-library. 37/ 38/ char * 39/ strncat(char *s1, const char *s2, size_t n) 40/ { 41/ char *os1 = s1; 42/ 43/ n++; 44/ while (*s1++) 45/ ; 46/ --s1; 47/ while (*s1++ = *s2++) 48/ if (--n == 0) { 49/ s1[-1] = '\0'; 50/ break; 51/ } 52/ return (os1); 53/ } 54/ 55/ In this assembly language version, the following expression is used 56/ to check if a 32-bit word data contains a null byte or not: 57/ (((A & 0x7f7f7f7f) + 0x7f7f7f7f) | A) & 0x80808080 58/ If the above expression geneates a value other than 0x80808080, 59/ that means the 32-bit word data contains a null byte. 60/ 61 62#include "SYS.h" 63 64 ENTRY(strncat) 65 pushl %edi / save register variables 66 pushl %esi 67 movl 12(%esp), %edi / %edi = destination string address 68 testl $3, %edi / if %edi not word aligned 69 jnz .L1 / goto .L1 70 .align 4 71.L2: 72 movl (%edi), %edx / move 1 word from (%edi) to %edx 73 movl $0x7f7f7f7f, %ecx 74 andl %edx, %ecx / %ecx = %edx & 0x7f7f7f7f 75 addl $4, %edi / next word 76 addl $0x7f7f7f7f, %ecx / %ecx += 0x7f7f7f7f 77 orl %edx, %ecx / %ecx |= %edx 78 andl $0x80808080, %ecx / %ecx &= 0x80808080 79 cmpl $0x80808080, %ecx / if no null byte in this word 80 je .L2 / goto .L2 81 subl $4, %edi / post-incremented 82.L1: 83 cmpb $0, (%edi) / if a byte in (%edi) is null 84 je .L3 / goto .L3 85 incl %edi / next byte 86 testl $3, %edi / if %edi not word aligned 87 jnz .L1 / goto .L1 88 jmp .L2 / goto .L2 (%edi word aligned) 89 .align 4 90.L3: 91 / %edi points to a null byte in destination string 92 movl 16(%esp), %eax / %eax = source string address 93 movl 20(%esp), %esi / %esi = number of bytes 94 95 testl $3, %eax / if %eax not word aligned 96 jnz .L4 / goto .L4 97 cmpl $4, %esi / if number of bytes < 4 98 jb .L7 / goto .L7 99 .align 4 100.L5: 101 movl (%eax), %edx / move 1 word from (%eax) to %edx 102 movl $0x7f7f7f7f, %ecx 103 andl %edx, %ecx / %ecx = %edx & 0x7f7f7f7f 104 addl $4, %eax / next word 105 addl $0x7f7f7f7f, %ecx / %ecx += 0x7f7f7f7f 106 orl %edx, %ecx / %ecx |= %edx 107 andl $0x80808080, %ecx / %ecx &= 0x80808080 108 cmpl $0x80808080, %ecx / if null byte in this word 109 jne .L6 / goto .L6 110 movl %edx, (%edi) / copy this word to (%edi) 111 subl $4, %esi / decrement number of bytes by 4 112 addl $4, %edi / next word 113 cmpl $4, %esi / if number of bytes >= 4 114 jae .L5 / goto .L5 115 jmp .L7 / goto .L7 116.L6: 117 subl $4, %eax / post-incremented 118 .align 4 119.L7: 120 / number of bytes < 4 or a null byte found in the word 121 cmpl $0, %esi / if number of bytes == 0 122 jz .L8 / goto .L8 (finished) 123 movb (%eax), %dl / %dl = a byte in (%eax) 124 decl %esi / decrement number of bytes by 1 125 movb %dl, (%edi) / copy %dl to (%edi) 126 incl %eax / next byte 127 incl %edi / next byte 128 cmpb $0, %dl / compare %dl with a null byte 129 je .L9 / if %dl is a null, goto .L9 130 jmp .L7 / goto .L7 131 .align 4 132 133.L4: 134 / %eax not aligned 135 cmpl $0, %esi / if number of bytes == 0 136 jz .L8 / goto .L8 (finished) 137 movb (%eax), %dl / %dl = a byte in (%eax) 138 decl %esi / decrement number of bytes by 1 139 movb %dl, (%edi) / copy %dl to (%edi) 140 incl %edi / next byte 141 incl %eax / next byte 142 cmpb $0, %dl / compare %dl with a null byte 143 je .L9 / if %dl is a null, goto .L9 144 jmp .L4 / goto .L4 145 .align 4 146.L8: 147 movb $0, (%edi) / null termination 148.L9: 149 movl 12(%esp), %eax / return the destination address 150 popl %esi / restore register variables 151 popl %edi 152 ret 153 SET_SIZE(strncat) 154