sdcc/device/lib/z80/strlen.s

   1 ;--------------------------------------------------------------------------
   2 ;  strlen.s
   3 ;
   4 ;  Copyright (C) 2008-2021, Philipp Klaus Krause
   5 ;
   6 ;  This library is free software; you can redistribute it and/or modify it
   7 ;  under the terms of the GNU General Public License as published by the
   8 ;  Free Software Foundation; either version 2, or (at your option) any
   9 ;  later version.
  10 ;
  11 ;  This library is distributed in the hope that it will be useful,
  12 ;  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 ;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14 ;  GNU General Public License for more details.
  15 ;
  16 ;  You should have received a copy of the GNU General Public License
  17 ;  along with this library; see the file COPYING. If not, write to the
  18 ;  Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  19 ;   MA 02110-1301, USA.
  20 ;
  21 ;  As a special exception, if you link this library with other files,
  22 ;  some of which are compiled with SDCC, to produce an executable,
  23 ;  this library does not by itself cause the resulting executable to
  24 ;  be covered by the GNU General Public License. This exception does
  25 ;  not however invalidate any other reasons why the executable file
  26 ;   might be covered by the GNU General Public License.
  27 ;--------------------------------------------------------------------------
  28
  29         .module strlen
  30         .optsdcc -mz80 sdcccall(1)
  31
  32         .area   _CODE
  33
  34         .globl _strlen
  35
  36 ; The Z80 has the cpir instruction, which is perfect for implementing strlen().
  37
  38 _strlen:
  39         xor     a, a
  40         ld      b, a
  41         ld      c, a
  42         cpir
  43         ld      hl, #-1
  44         sbc     hl, bc  ; C flag still cleared from xor above.
  45         ex      de, hl
  46         ret
  47