root/arch/alpha/lib/strncat.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * arch/alpha/lib/strncat.S
   4  * Contributed by Richard Henderson (rth@tamu.edu)
   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 #include <asm/export.h>
  14         .text
  15 
  16         .align 3
  17         .globl strncat
  18         .ent strncat
  19 strncat:
  20         .frame $30, 0, $26
  21         .prologue 0
  22 
  23         mov     $16, $0         # set up return value
  24         beq     $18, $zerocount
  25 
  26         /* Find the end of the string.  */
  27 
  28         ldq_u   $1, 0($16)      # load first quadword ($16 may be misaligned)
  29         lda     $2, -1($31)
  30         insqh   $2, $16, $2
  31         andnot  $16, 7, $16
  32         or      $2, $1, $1
  33         cmpbge  $31, $1, $2     # bits set iff byte == 0
  34         bne     $2, $found
  35 
  36 $loop:  ldq     $1, 8($16)
  37         addq    $16, 8, $16
  38         cmpbge  $31, $1, $2
  39         beq     $2, $loop
  40 
  41 $found: negq    $2, $3          # clear all but least set bit
  42         and     $2, $3, $2
  43 
  44         and     $2, 0xf0, $3    # binary search for that set bit
  45         and     $2, 0xcc, $4
  46         and     $2, 0xaa, $5
  47         cmovne  $3, 4, $3
  48         cmovne  $4, 2, $4
  49         cmovne  $5, 1, $5
  50         addq    $3, $4, $3
  51         addq    $16, $5, $16
  52         addq    $16, $3, $16
  53 
  54         /* Now do the append.  */
  55 
  56         bsr     $23, __stxncpy
  57 
  58         /* Worry about the null termination.  */
  59 
  60         zapnot  $1, $27, $2     # was last byte a null?
  61         bne     $2, 0f
  62         ret
  63 
  64 0:      cmplt   $27, $24, $2    # did we fill the buffer completely?
  65         or      $2, $18, $2
  66         bne     $2, 2f
  67 
  68         and     $24, 0x80, $2   # no zero next byte
  69         bne     $2, 1f
  70 
  71         /* Here there are bytes left in the current word.  Clear one.  */
  72         addq    $24, $24, $24   # end-of-count bit <<= 1
  73 2:      zap     $1, $24, $1
  74         stq_u   $1, 0($16)
  75         ret
  76 
  77 1:      /* Here we must read the next DST word and clear the first byte.  */
  78         ldq_u   $1, 8($16)
  79         zap     $1, 1, $1
  80         stq_u   $1, 8($16)
  81 
  82 $zerocount:
  83         ret
  84 
  85         .end strncat
  86         EXPORT_SYMBOL(strncat)