LXR linux/arch/alpha/lib/ev67-strncat.S

   1/*
   2 * arch/alpha/lib/ev67-strncat.S
   3 * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
   4 *
   5 * Append no more than COUNT characters from the null-terminated string SRC
   6 * to the null-terminated string DST.  Always null-terminate the new DST.
   7 *
   8 * This differs slightly from the semantics in libc in that we never write
   9 * past count, whereas libc may write to count+1.  This follows the generic
  10 * implementation in lib/string.c and is, IMHO, more sensible.
  11 *
  12 * Much of the information about 21264 scheduling/coding comes from:
  13 *      Compiler Writer's Guide for the Alpha 21264
  14 *      abbreviated as 'CWG' in other comments here
  15 *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  16 * Scheduling notation:
  17 *      E       - either cluster
  18 *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  19 *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  20 * Try not to change the actual algorithm if possible for consistency.
  21 */
  22
  23
  24        .text
  25
  26        .align 4
  27        .globl strncat
  28        .ent strncat
  29strncat:
  30        .frame $30, 0, $26
  31        .prologue 0
  32
  33        mov     $16, $0         # set up return value
  34        beq     $18, $zerocount # U :
  35        /* Find the end of the string.  */
  36        ldq_u   $1, 0($16)      # L : load first quadword ($16 may be misaligned)
  37        lda     $2, -1($31)     # E :
  38
  39        insqh   $2, $0, $2      # U :
  40        andnot  $16, 7, $16     # E :
  41        nop                     # E :
  42        or      $2, $1, $1      # E :
  43
  44        nop                     # E :
  45        nop                     # E :
  46        cmpbge  $31, $1, $2     # E : bits set iff byte == 0
  47        bne     $2, $found      # U :
  48
  49$loop:  ldq     $1, 8($16)      # L :
  50        addq    $16, 8, $16     # E :
  51        cmpbge  $31, $1, $2     # E :
  52        beq     $2, $loop       # U :
  53
  54$found: cttz    $2, $3          # U0 :
  55        addq    $16, $3, $16    # E :
  56        nop                     # E :
  57        bsr     $23, __stxncpy  # L0 :/* Now do the append.  */
  58
  59        /* Worry about the null termination.  */
  60
  61        zapnot  $1, $27, $2     # U : was last byte a null?
  62        cmplt   $27, $24, $5    # E : did we fill the buffer completely?
  63        bne     $2, 0f          # U :
  64        ret                     # L0 :
  65
  660:      or      $5, $18, $2     # E :
  67        nop
  68        bne     $2, 2f          # U :
  69        and     $24, 0x80, $3   # E : no zero next byte
  70
  71        nop                     # E :
  72        bne     $3, 1f          # U :
  73        /* Here there are bytes left in the current word.  Clear one.  */
  74        addq    $24, $24, $24   # E : end-of-count bit <<= 1
  75        nop                     # E :
  76
  772:      zap     $1, $24, $1     # U :
  78        nop                     # E :
  79        stq_u   $1, 0($16)      # L :
  80        ret                     # L0 :
  81
  821:      /* Here we must clear the first byte of the next DST word */
  83        stb     $31, 8($16)     # L :
  84        nop                     # E :
  85        nop                     # E :
  86        ret                     # L0 :
  87
  88$zerocount:
  89        nop                     # E :
  90        nop                     # E :
  91        nop                     # E :
  92        ret                     # L0 :
  93
  94        .end strncat
  95