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

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * arch/alpha/lib/ev67-strncat.S
   4  * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
   5  *
   6  * Append no more than COUNT characters from the null-terminated string SRC
   7  * to the null-terminated string DST.  Always null-terminate the new DST.
   8  *
   9  * This differs slightly from the semantics in libc in that we never write
  10  * past count, whereas libc may write to count+1.  This follows the generic
  11  * implementation in lib/string.c and is, IMHO, more sensible.
  12  *
  13  * Much of the information about 21264 scheduling/coding comes from:
  14  *      Compiler Writer's Guide for the Alpha 21264
  15  *      abbreviated as 'CWG' in other comments here
  16  *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  17  * Scheduling notation:
  18  *      E       - either cluster
  19  *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  20  *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  21  * Try not to change the actual algorithm if possible for consistency.
  22  */
  23 
  24 #include <asm/export.h>
  25         .text
  26 
  27         .align 4
  28         .globl strncat
  29         .ent strncat
  30 strncat:
  31         .frame $30, 0, $26
  32         .prologue 0
  33 
  34         mov     $16, $0         # set up return value
  35         beq     $18, $zerocount # U :
  36         /* Find the end of the string.  */
  37         ldq_u   $1, 0($16)      # L : load first quadword ($16 may be misaligned)
  38         lda     $2, -1($31)     # E :
  39 
  40         insqh   $2, $0, $2      # U :
  41         andnot  $16, 7, $16     # E :
  42         nop                     # E :
  43         or      $2, $1, $1      # E :
  44 
  45         nop                     # E :
  46         nop                     # E :
  47         cmpbge  $31, $1, $2     # E : bits set iff byte == 0
  48         bne     $2, $found      # U :
  49 
  50 $loop:  ldq     $1, 8($16)      # L :
  51         addq    $16, 8, $16     # E :
  52         cmpbge  $31, $1, $2     # E :
  53         beq     $2, $loop       # U :
  54 
  55 $found: cttz    $2, $3          # U0 :
  56         addq    $16, $3, $16    # E :
  57         nop                     # E :
  58         bsr     $23, __stxncpy  # L0 :/* Now do the append.  */
  59 
  60         /* Worry about the null termination.  */
  61 
  62         zapnot  $1, $27, $2     # U : was last byte a null?
  63         cmplt   $27, $24, $5    # E : did we fill the buffer completely?
  64         bne     $2, 0f          # U :
  65         ret                     # L0 :
  66 
  67 0:      or      $5, $18, $2     # E :
  68         nop
  69         bne     $2, 2f          # U :
  70         and     $24, 0x80, $3   # E : no zero next byte
  71 
  72         nop                     # E :
  73         bne     $3, 1f          # U :
  74         /* Here there are bytes left in the current word.  Clear one.  */
  75         addq    $24, $24, $24   # E : end-of-count bit <<= 1
  76         nop                     # E :
  77 
  78 2:      zap     $1, $24, $1     # U :
  79         nop                     # E :
  80         stq_u   $1, 0($16)      # L :
  81         ret                     # L0 :
  82 
  83 1:      /* Here we must clear the first byte of the next DST word */
  84         stb     $31, 8($16)     # L :
  85         nop                     # E :
  86         nop                     # E :
  87         ret                     # L0 :
  88 
  89 $zerocount:
  90         nop                     # E :
  91         nop                     # E :
  92         nop                     # E :
  93         ret                     # L0 :
  94 
  95         .end strncat
  96         EXPORT_SYMBOL(strncat)