root/arch/alpha/lib/ev67-strcat.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * arch/alpha/lib/ev67-strcat.S
   4  * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
   5  *
   6  * Append a null-terminated string from SRC to DST.
   7  *
   8  * Much of the information about 21264 scheduling/coding comes from:
   9  *      Compiler Writer's Guide for the Alpha 21264
  10  *      abbreviated as 'CWG' in other comments here
  11  *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  12  * Scheduling notation:
  13  *      E       - either cluster
  14  *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  15  *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  16  * Try not to change the actual algorithm if possible for consistency.
  17  * Commentary: It seems bogus to walk the input string twice - once
  18  * to determine the length, and then again while doing the copy.
  19  * A significant (future) enhancement would be to only read the input
  20  * string once.
  21  */
  22 
  23 #include <asm/export.h>
  24         .text
  25 
  26         .align 4
  27         .globl strcat
  28         .ent strcat
  29 strcat:
  30         .frame $30, 0, $26
  31         .prologue 0
  32 
  33         mov     $16, $0         # E : set up return value
  34         /* Find the end of the string.  */
  35         ldq_u   $1, 0($16)      # L : load first quadword (a0 may be misaligned)
  36         lda     $2, -1          # E :
  37         insqh   $2, $16, $2     # U :
  38 
  39         andnot  $16, 7, $16     # E :
  40         or      $2, $1, $1      # E :
  41         cmpbge  $31, $1, $2     # E : bits set iff byte == 0
  42         bne     $2, $found      # U :
  43 
  44 $loop:  ldq     $1, 8($16)      # L :
  45         addq    $16, 8, $16     # E :
  46         cmpbge  $31, $1, $2     # E :
  47         beq     $2, $loop       # U :
  48 
  49 $found: cttz    $2, $3          # U0 :
  50         addq    $16, $3, $16    # E :
  51         /* Now do the append.  */
  52         mov     $26, $23        # E :
  53         br      __stxcpy        # L0 :
  54 
  55         .end strcat
  56         EXPORT_SYMBOL(strcat)