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/*

 * arch/alpha/lib/ev67-strncat.S

 * 21264 version contributed by Rick Gorton 

 *

 * 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