root/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
  28 strlen:
  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)