/*
 * Written by J.T. Conklin <jtc@acorntoolworks.com>
 * Public domain.
 */

#include <machine/asm.h>

#if defined(LIBC_SCCS)
        RCSID("$NetBSD: strcpy.S,v 1.2 2014/03/22 19:38:46 jakllsch Exp $")
#endif

/*
 * This strcpy implementation copies a byte at a time until the
 * source pointer is aligned to a word boundary, it then copies by
 * words until it finds a word containing a zero byte, and finally
 * copies by bytes until the end of the string is reached.
 *
 * While this may result in unaligned stores if the source and
 * destination pointers are unaligned with respect to each other,
 * it is still faster than either byte copies or the overhead of
 * an implementation suitable for machines with strict alignment
 * requirements.
 */

ENTRY(strcpy)
        pushl   %ebx
        movl    8(%esp),%ecx
        movl    12(%esp),%eax

        /*
         * Align source to a word boundary.
         * Consider unrolling loop?
         */
        _ALIGN_TEXT
.Lalign:
        testl   $3,%eax
        je      .Lword_aligned
        movb    (%eax),%bl
        incl    %eax
        movb    %bl,(%ecx)
        incl    %ecx
        testb   %bl,%bl
        jne     .Lalign
        jmp     .Ldone

        _ALIGN_TEXT
.Lloop:
        movl    %ebx,(%ecx)
        addl    $4,%ecx
.Lword_aligned:
        movl    (%eax),%ebx
        addl    $4,%eax
        leal    -0x01010101(%ebx),%edx
        testl   $0x80808080,%edx
        je      .Lloop

        /*
         * In rare cases, the above loop may exit prematurely. We must
         * return to the loop if none of the bytes in the word equal 0.
         */

        movb    %bl,(%ecx)
        incl    %ecx
        testb   %bl,%bl
        je      .Ldone

        movb    %bh,(%ecx)
        incl    %ecx
        testb   %bh,%bh
        je      .Ldone

        shrl    $16,%ebx
        movb    %bl,(%ecx)
        incl    %ecx
        testb   %bl,%bl
        je      .Ldone

        movb    %bh,(%ecx)
        incl    %ecx
        testb   %bh,%bh
        jne     .Lword_aligned

.Ldone:
        movl    8(%esp),%eax
        popl    %ebx
        ret
END(strcpy)