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

   1/* SPDX-License-Identifier: GPL-2.0 */
   2/*
   3 * arch/alpha/lib/ev67-strlen.S
   4 * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
   5 *
   6 * Finds length of a 0-terminated string.  Optimized for the
   7 * Alpha architecture:
   8 *
   9 *      - memory accessed as aligned quadwords only
  10 *      - uses bcmpge to compare 8 bytes in parallel
  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 */
  21#include <asm/export.h>
  22        .set noreorder
  23        .set noat
  24
  25        .globl  strlen
  26        .ent    strlen
  27        .align 4
  28strlen:
  29        ldq_u   $1, 0($16)      # L : load first quadword ($16  may be misaligned)
  30        lda     $2, -1($31)     # E :
  31        insqh   $2, $16, $2     # U :
  32        andnot  $16, 7, $0      # E :
  33
  34        or      $2, $1, $1      # E :
  35        cmpbge  $31, $1, $2     # E : $2  <- bitmask: bit i == 1 <==> i-th byte == 0
  36        nop                     # E :
  37        bne     $2, $found      # U :
  38
  39$loop:  ldq     $1, 8($0)       # L :
  40        addq    $0, 8, $0       # E : addr += 8
  41        cmpbge  $31, $1, $2     # E :
  42        beq     $2, $loop       # U :
  43
  44$found:
  45        cttz    $2, $3          # U0 :
  46        addq    $0, $3, $0      # E :
  47        subq    $0, $16, $0     # E :
  48        ret     $31, ($26)      # L0 :
  49
  50        .end    strlen
  51        EXPORT_SYMBOL(strlen)
  52