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

#include <machine/asm.h>

#if defined(LIBC_SCCS)
        RCSID("$NetBSD: strchr.S,v 1.3 2014/03/22 19:38:46 jakllsch Exp $")
#endif

ENTRY(strchr)
        pushl   %esi
        pushl   %ebx
        movl    12(%esp),%eax
        movzbl  16(%esp),%ecx

        /*
         * Align to word boundary.
         * Consider unrolling loop?
         */
.Lalign:
        testb   $3,%al
        je      .Lword_aligned
        movb    (%eax),%bl
        cmpb    %cl,%bl
        je      .Ldone
        testb   %bl,%bl
        je      .Lzero
        incl    %eax
        jmp     .Lalign

.Lword_aligned:
        /* copy char to all bytes in word */
        movb    %cl,%ch
        movl    %ecx,%edx
        sall    $16,%ecx
        orl     %edx,%ecx

        /* Check whether any byte in the word is equal to ch or 0. */
        _ALIGN_TEXT
.Lloop:
        movl    (%eax),%ebx
        addl    $4,%eax
        movl    %ebx,%esi
        leal    -0x01010101(%ebx),%edx
        xorl    %ecx,%esi
        subl    $0x01010101,%esi
        orl     %esi,%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 match
         * ch or are equal to 0.
         */

        /*
         * Alignment here avoids a stall on the Athlon, even though
         * it's not a branch target.
         */

        _ALIGN_TEXT
        cmpb    %cl,%bl         /* 1st byte == ch? */
        jne     1f
        subl    $4,%eax
        jmp     .Ldone
1:      testb   %bl,%bl         /* 1st byte == 0? */
        je      .Lzero

        cmpb    %cl,%bh         /* 2nd byte == ch? */
        jne     1f
        subl    $3,%eax
        jmp     .Ldone
1:      testb   %bh,%bh         /* 2nd byte == 0? */
        je      .Lzero

        shrl    $16,%ebx
        cmpb    %cl,%bl         /* 3rd byte == ch? */
        jne     1f
        subl    $2,%eax
        jmp     .Ldone
1:      testb   %bl,%bl         /* 3rd byte == 0? */
        je      .Lzero

        cmpb    %cl,%bh         /* 4th byte == ch? */
        jne     1f
        decl    %eax
        jmp     .Ldone
1:      testb   %bh,%bh         /* 4th byte == 0? */
        jne     .Lloop

.Lzero:
        /* If a ch wasn't found, return 0. */
        xorl    %eax,%eax

.Ldone:
        popl    %ebx
        popl    %esi
        ret
END(strchr)

STRONG_ALIAS(index,strchr)