LXR linux/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
  30strncat:
  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
  670:      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
  782:      zap     $1, $24, $1     # U :
  79        nop                     # E :
  80        stq_u   $1, 0($16)      # L :
  81        ret                     # L0 :
  82
  831:      /* 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)
  97