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/ The above has been extended for 64-bit support. 62/ 63 64#include "SYS.h" 65 66 ENTRY(strncat) /* (char *, char *, size_t) */ 67 movq %rdi, %rax / save return value 68 movabsq $0x7f7f7f7f7f7f7f7f, %r8 / %r8 = 0x7f... 69 movq %r8, %r9 70 notq %r9 / %r9 = 0x80... 71 testq $7, %rdi / if %rdi not quadword aligned 72 jnz .L1 / goto .L1 73 .align 4 74.L2: 75 movq (%rdi), %r11 / move 1 quadword from (%rdi) to %r11 76 movq %r8, %rcx 77 andq %r11, %rcx / %rcx = %r11 & 0x7f7f7f7f 78 addq $8, %rdi / next quadword 79 addq %r8, %rcx / %rcx += 0x7f7f7f7f 80 orq %r11, %rcx / %rcx |= %r11 81 andq %r9, %rcx / %rcx &= 0x80808080 82 cmpq %r9, %rcx / if no null byte in this quadword 83 je .L2 / goto .L2 84 subq $8, %rdi / post-incremented 85.L1: 86 cmpb $0, (%rdi) / if a byte in (%rdi) is null 87 je .L3 / goto .L3 88 incq %rdi / next byte 89 testq $7, %rdi / if %rdi not quadword aligned 90 jnz .L1 / goto .L1 91 jmp .L2 / goto .L2 (%rdi quadword aligned) 92 .align 4 93.L3: 94 / %rdi points to a null byte in destination string 95 96 testq $7, %rsi / if %rsi not quadword aligned 97 jnz .L4 / goto .L4 98 cmpq $8, %rdx / if number of bytes < 8 99 jb .L7 / goto .L7 100 .align 4 101.L5: 102 movq (%rsi), %r11 / move 1 quadword from (%rsi) to %r11 103 movq %r8, %rcx 104 andq %r11, %rcx / %rcx = %r11 & 0x7f7f7f7f 105 addq $8, %rsi / next quadword 106 addq %r8, %rcx / %rcx += 0x7f7f7f7f 107 orq %r11, %rcx / %rcx |= %r11 108 andq %r9, %rcx / %rcx &= 0x80808080 109 cmpq %r9, %rcx / if null byte in this quadword 110 jne .L6 / goto .L6 111 movq %r11, (%rdi) / copy this quadword to (%rdi) 112 subq $8, %rdx / decrement number of bytes by 8 113 addq $8, %rdi / next quadword 114 cmpq $8, %rdx / if number of bytes >= 8 115 jae .L5 / goto .L5 116 jmp .L7 / goto .L7 117.L6: 118 subq $8, %rsi / post-incremented 119 .align 4 120.L7: 121 / number of bytes < 8 or a null byte found in the quadword 122 cmpq $0, %rdx / if number of bytes == 0 123 jz .L8 / goto .L8 (finished) 124 movb (%rsi), %r11b / %r11b = a byte in (%rsi) 125 decq %rdx / decrement number of bytes by 1 126 movb %r11b, (%rdi) / copy %r11b to (%rdi) 127 incq %rsi / next byte 128 incq %rdi / next byte 129 cmpb $0, %r11b / compare %r11b with a null byte 130 je .L9 / if %r11b is a null, goto .L9 131 jmp .L7 / goto .L7 132 .align 4 133 134.L4: 135 / %rsi not aligned 136 cmpq $0, %rdx / if number of bytes == 0 137 jz .L8 / goto .L8 (finished) 138 movb (%rsi), %r11b / %r11b = a byte in (%rsi) 139 decq %rdx / decrement number of bytes by 1 140 movb %r11b, (%rdi) / copy %r11b to (%rdi) 141 incq %rdi / next byte 142 incq %rsi / next byte 143 cmpb $0, %r11b / compare %r11b with a null byte 144 je .L9 / if %r11b is a null, goto .L9 145 jmp .L4 / goto .L4 146 .align 4 147.L8: 148 movb $0, (%rdi) / null termination 149.L9: 150 ret 151 SET_SIZE(strncat) 152