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

   1/*
   2 * arch/alpha/lib/ev67-strlen.S
   3 * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
   4 *
   5 * Finds length of a 0-terminated string.  Optimized for the
   6 * Alpha architecture:
   7 *
   8 *      - memory accessed as aligned quadwords only
   9 *      - uses bcmpge to compare 8 bytes in parallel
  10 *
  11 * Much of the information about 21264 scheduling/coding comes from:
  12 *      Compiler Writer's Guide for the Alpha 21264
  13 *      abbreviated as 'CWG' in other comments here
  14 *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  15 * Scheduling notation:
  16 *      E       - either cluster
  17 *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  18 *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  19 */
  20
  21        .set noreorder
  22        .set noat
  23
  24        .globl  strlen
  25        .ent    strlen
  26        .align 4
  27strlen:
  28        ldq_u   $1, 0($16)      # L : load first quadword ($16  may be misaligned)
  29        lda     $2, -1($31)     # E :
  30        insqh   $2, $16, $2     # U :
  31        andnot  $16, 7, $0      # E :
  32
  33        or      $2, $1, $1      # E :
  34        cmpbge  $31, $1, $2     # E : $2  <- bitmask: bit i == 1 <==> i-th byte == 0
  35        nop                     # E :
  36        bne     $2, $found      # U :
  37
  38$loop:  ldq     $1, 8($0)       # L :
  39        addq    $0, 8, $0       # E : addr += 8
  40        cmpbge  $31, $1, $2     # E :
  41        beq     $2, $loop       # U :
  42
  43$found:
  44        cttz    $2, $3          # U0 :
  45        addq    $0, $3, $0      # E :
  46        subq    $0, $16, $0     # E :
  47        ret     $31, ($26)      # L0 :
  48
  49        .end    strlen
  50