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/*
 * arch/alpha/lib/ev67-strncat.S
 * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
 *
 * 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.
 *
 * Much of the information about 21264 scheduling/coding comes from:
 *      Compiler Writer's Guide for the Alpha 21264
 *      abbreviated as 'CWG' in other comments here
 *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
 * Scheduling notation:
 *      E       - either cluster
 *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
 *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
 * Try not to change the actual algorithm if possible for consistency.
 */


        .text

        .align 4
        .globl strncat
        .ent strncat
strncat:
        .frame $30, 0, $26
        .prologue 0

        mov     $16, $0         # set up return value
        beq     $18, $zerocount # U :
        /* Find the end of the string.  */
        ldq_u   $1, 0($16)      # L : load first quadword ($16 may be misaligned)
        lda     $2, -1($31)     # E :

        insqh   $2, $0, $2      # U :
        andnot  $16, 7, $16     # E :
        nop                     # E :
        or      $2, $1, $1      # E :

        nop                     # E :
        nop                     # E :
        cmpbge  $31, $1, $2     # E : bits set iff byte == 0
        bne     $2, $found      # U :

$loop:  ldq     $1, 8($16)      # L :
        addq    $16, 8, $16     # E :
        cmpbge  $31, $1, $2     # E :
        beq     $2, $loop       # U :

$found: cttz    $2, $3          # U0 :
        addq    $16, $3, $16    # E :
        nop                     # E :
        bsr     $23, __stxncpy  # L0 :/* Now do the append.  */

        /* Worry about the null termination.  */

        zapnot  $1, $27, $2     # U : was last byte a null?
        cmplt   $27, $24, $5    # E : did we fill the buffer completely?
        bne     $2, 0f          # U :
        ret                     # L0 :

0:      or      $5, $18, $2     # E :
        nop
        bne     $2, 2f          # U :
        and     $24, 0x80, $3   # E : no zero next byte

        nop                     # E :
        bne     $3, 1f          # U :
        /* Here there are bytes left in the current word.  Clear one.  */
        addq    $24, $24, $24   # E : end-of-count bit <<= 1
        nop                     # E :

2:      zap     $1, $24, $1     # U :
        nop                     # E :
        stq_u   $1, 0($16)      # L :
        ret                     # L0 :

1:      /* Here we must clear the first byte of the next DST word */
        stb     $31, 8($16)     # L :
        nop                     # E :
        nop                     # E :
        ret                     # L0 :

$zerocount:
        nop                     # E :
        nop                     # E :
        nop                     # E :
        ret                     # L0 :

        .end strncat