/*      $OpenBSD: strcmp.S,v 1.6 2022/12/07 19:26:39 guenther Exp $     */
/*      $NetBSD: strcmp.S,v 1.2 2014/03/22 19:16:34 jakllsch Exp $      */

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

#include <machine/asm.h>

ENTRY(strcmp)
        RETGUARD_SETUP(strcmp, r10)
        /*
         * Align s1 to word boundary.
         * Consider unrolling loop?
         */
.Ls1align:
        testb   $7,%dil
        je      .Ls1aligned
        movb    (%rdi),%al
        incq    %rdi
        movb    (%rsi),%dl
        incq    %rsi
        testb   %al,%al
        je      .Ldone
        cmpb    %al,%dl
        je      .Ls1align
        jmp     .Ldone

        /*
         * Check whether s2 is aligned to a word boundary.  If it is, we
         * can compare by words.  Otherwise we have to compare by bytes.
         */
.Ls1aligned:
        testb   $7,%sil
        jne     .Lbyte_loop

        movabsq $0x0101010101010101,%r8
        subq    $8,%rdi
        movabsq $0x8080808080808080,%r9
        subq    $8,%rsi

        _ALIGN_TEXT
.Lword_loop:
        movq    8(%rdi),%rax
        addq    $8,%rdi
        movq    8(%rsi),%rdx
        addq    $8,%rsi
        cmpq    %rax,%rdx
        jne     .Lbyte_loop
        subq    %r8,%rdx
        notq    %rax
        andq    %rax,%rdx
        testq   %r9,%rdx
        je      .Lword_loop

        _ALIGN_TEXT
.Lbyte_loop:
        movb    (%rdi),%al
        incq    %rdi
        movb    (%rsi),%dl
        incq    %rsi
        testb   %al,%al
        je      .Ldone
        cmpb    %al,%dl
        je      .Lbyte_loop

.Ldone:
        movzbq  %al,%rax
        movzbq  %dl,%rdx
        subq    %rdx,%rax
        RETGUARD_CHECK(strcmp, r10)
        ret
        lfence
END(strcmp)