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/*
 * arch/alpha/lib/strncat.S
 * Contributed by Richard Henderson (rth@tamu.edu)
 *
 * Append no more than COUNT characters from the null-terminated string SRC
 * to the null-terminated string DST.  Always null-terminate the new DST.
 *
 * This differs slightly from the semantics in libc in that we never write
 * past count, whereas libc may write to count+1.  This follows the generic
 * implementation in lib/string.c and is, IMHO, more sensible.
 */

        .text

        .align 3
        .globl strncat
        .ent strncat
strncat:
        .frame $30, 0, $26
        .prologue 0

        mov     $16, $0         # set up return value
        beq     $18, $zerocount

        /* Find the end of the string.  */

        ldq_u   $1, 0($16)      # load first quadword ($16 may be misaligned)
        lda     $2, -1($31)
        insqh   $2, $16, $2
        andnot  $16, 7, $16
        or      $2, $1, $1
        cmpbge  $31, $1, $2     # bits set iff byte == 0
        bne     $2, $found

$loop:  ldq     $1, 8($16)
        addq    $16, 8, $16
        cmpbge  $31, $1, $2
        beq     $2, $loop

$found: negq    $2, $3          # clear all but least set bit
        and     $2, $3, $2

        and     $2, 0xf0, $3    # binary search for that set bit
        and     $2, 0xcc, $4
        and     $2, 0xaa, $5
        cmovne  $3, 4, $3
        cmovne  $4, 2, $4
        cmovne  $5, 1, $5
        addq    $3, $4, $3
        addq    $16, $5, $16
        addq    $16, $3, $16

        /* Now do the append.  */

        bsr     $23, __stxncpy

        /* Worry about the null termination.  */

        zapnot  $1, $27, $2     # was last byte a null?
        bne     $2, 0f
        ret

0:      cmplt   $27, $24, $2    # did we fill the buffer completely?
        or      $2, $18, $2
        bne     $2, 2f

        and     $24, 0x80, $2   # no zero next byte
        bne     $2, 1f

        /* Here there are bytes left in the current word.  Clear one.  */
        addq    $24, $24, $24   # end-of-count bit <<= 1
2:      zap     $1, $24, $1
        stq_u   $1, 0($16)
        ret

1:      /* Here we must read the next DST word and clear the first byte.  */
        ldq_u   $1, 8($16)
        zap     $1, 1, $1
        stq_u   $1, 8($16)

$zerocount:
        ret

        .end strncat