LXR linux/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
  19strncat:
  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
  640:      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
  732:      zap     $1, $24, $1
  74        stq_u   $1, 0($16)
  75        ret
  76
  771:      /* 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)
  87