/*
 * 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 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

        .file   "strcpy.s"

/
/ strcpy(s1, s2)
/
/ Copies string s2 to s1.  s1 must be large enough.
/ Returns s1
/
/
/ Fast assembly language version of the following C-program strcpy
/ which represents the `standard' for the C-library.
/
/       char *
/       strcpy(char *s1, const char *s2)
/       {
/               char    *os1 = s1;
/
/               while (*s1++ = *s2++)
/                       ;
/               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.
/

#include "SYS.h"

        ENTRY(strcpy)
        push    %edi                            / save reg as per calling cvntn
        mov     12(%esp), %ecx                  / src ptr
        mov     8(%esp), %edi                   / dst ptr
        mov     %ecx, %eax                      / src
        sub     %edi, %ecx                      / src - dst
        and     $3, %eax                        / check src alignment
        jz      load
        sub     $4, %eax

byte_loop:
        movb    (%edi, %ecx, 1), %dl            / load src byte
        movb    %dl, (%edi)                     / load dest byte
        inc     %edi                            / increment src and dest
        testb   %dl, %dl                        / is src zero?
        jz      done
        inc     %eax                            / check src alignment
        jnz     byte_loop
        jmp     load

store:
        mov     %eax, (%edi)                    / store word
        add     $4, %edi                        / incrment src and dest by 4
load:
        mov     (%edi, %ecx, 1), %eax           / load word
        lea     -0x01010101(%eax), %edx         / (word - 0x01010101)
        not     %eax                            / ~word
        and     %eax, %edx                      / (word - 0x01010101) & ~word
        not     %eax                            / word
        and     $0x80808080, %edx       / (wd - 0x01010101) & ~wd & 0x80808080
        jz      store                           / store word w/o zero byte

has_zero_byte:
        movb    %al, (%edi)                     / store first byte
        testb   %al, %al                        / check first byte for zero
        jz      done
        movb    %ah, 1(%edi)                    / continue storing and checking
        testb   %ah, %ah
        jz      done
        shr     $16, %eax                       / grab last two bytes
        movb    %al, 2(%edi)
        testb   %al, %al
        jz      done
        movb    %ah, 3(%edi)
done:
        mov     8(%esp), %eax                   / return ptr to dest
        pop     %edi                            / restore as per calling cvntn
        ret
        SET_SIZE(strcpy)