/*
 * 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)