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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
.file "strncat.s"
/
/ strncat(s1, s2, n)
/
/ Concatenates s2 on the end of s1. s1's space must be large enough.
/ At most n characters are moved.
/ Returns s1.
/
/ Fast assembly language version of the following C-program strncat
/ which represents the `standard' for the C-library.
/
/ char *
/ strncat(char *s1, const char *s2, size_t n)
/ {
/ char *os1 = s1;
/
/ n++;
/ while (*s1++)
/ ;
/ --s1;
/ while (*s1++ = *s2++)
/ if (--n == 0) {
/ s1[-1] = '\0';
/ break;
/ }
/ return (os1);
/ }
/
/ In this assembly language version, the following expression is used
/ to check if a 32-bit word data contains a null byte or not:
/ (((A & 0x7f7f7f7f) + 0x7f7f7f7f) | A) & 0x80808080
/ If the above expression geneates a value other than 0x80808080,
/ that means the 32-bit word data contains a null byte.
/
/ The above has been extended for 64-bit support.
/
#include "SYS.h"
ENTRY(strncat) /* (char *, char *, size_t) */
movq %rdi, %rax / save return value
movabsq $0x7f7f7f7f7f7f7f7f, %r8 / %r8 = 0x7f...
movq %r8, %r9
notq %r9 / %r9 = 0x80...
testq $7, %rdi / if %rdi not quadword aligned
jnz .L1 / goto .L1
.align 4
.L2:
movq (%rdi), %r11 / move 1 quadword from (%rdi) to %r11
movq %r8, %rcx
andq %r11, %rcx / %rcx = %r11 & 0x7f7f7f7f
addq $8, %rdi / next quadword
addq %r8, %rcx / %rcx += 0x7f7f7f7f
orq %r11, %rcx / %rcx |= %r11
andq %r9, %rcx / %rcx &= 0x80808080
cmpq %r9, %rcx / if no null byte in this quadword
je .L2 / goto .L2
subq $8, %rdi / post-incremented
.L1:
cmpb $0, (%rdi) / if a byte in (%rdi) is null
je .L3 / goto .L3
incq %rdi / next byte
testq $7, %rdi / if %rdi not quadword aligned
jnz .L1 / goto .L1
jmp .L2 / goto .L2 (%rdi quadword aligned)
.align 4
.L3:
/ %rdi points to a null byte in destination string
testq $7, %rsi / if %rsi not quadword aligned
jnz .L4 / goto .L4
cmpq $8, %rdx / if number of bytes < 8
jb .L7 / goto .L7
.align 4
.L5:
movq (%rsi), %r11 / move 1 quadword from (%rsi) to %r11
movq %r8, %rcx
andq %r11, %rcx / %rcx = %r11 & 0x7f7f7f7f
addq $8, %rsi / next quadword
addq %r8, %rcx / %rcx += 0x7f7f7f7f
orq %r11, %rcx / %rcx |= %r11
andq %r9, %rcx / %rcx &= 0x80808080
cmpq %r9, %rcx / if null byte in this quadword
jne .L6 / goto .L6
movq %r11, (%rdi) / copy this quadword to (%rdi)
subq $8, %rdx / decrement number of bytes by 8
addq $8, %rdi / next quadword
cmpq $8, %rdx / if number of bytes >= 8
jae .L5 / goto .L5
jmp .L7 / goto .L7
.L6:
subq $8, %rsi / post-incremented
.align 4
.L7:
/ number of bytes < 8 or a null byte found in the quadword
cmpq $0, %rdx / if number of bytes == 0
jz .L8 / goto .L8 (finished)
movb (%rsi), %r11b / %r11b = a byte in (%rsi)
decq %rdx / decrement number of bytes by 1
movb %r11b, (%rdi) / copy %r11b to (%rdi)
incq %rsi / next byte
incq %rdi / next byte
cmpb $0, %r11b / compare %r11b with a null byte
je .L9 / if %r11b is a null, goto .L9
jmp .L7 / goto .L7
.align 4
.L4:
/ %rsi not aligned
cmpq $0, %rdx / if number of bytes == 0
jz .L8 / goto .L8 (finished)
movb (%rsi), %r11b / %r11b = a byte in (%rsi)
decq %rdx / decrement number of bytes by 1
movb %r11b, (%rdi) / copy %r11b to (%rdi)
incq %rdi / next byte
incq %rsi / next byte
cmpb $0, %r11b / compare %r11b with a null byte
je .L9 / if %r11b is a null, goto .L9
jmp .L4 / goto .L4
.align 4
.L8:
movb $0, (%rdi) / null termination
.L9:
ret
SET_SIZE(strncat)
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