sdcc/device/lib/mos65c02/_mulint.s

   1 ;-------------------------------------------------------------------------
   2 ;   _mulint.s - routine for multiplication of 16 bit (unsigned) int
   3 ;
   4 ;   Copyright (C) 2009, Ullrich von Bassewitz
   5 ;   Copyright (C) 2022, Gabriele Gorla
   6 ;
   7 ;   This library is free software; you can redistribute it and/or modify it
   8 ;   under the terms of the GNU General Public License as published by the
   9 ;   Free Software Foundation; either version 2, or (at your option) any
  10 ;   later version.
  11 ;
  12 ;   This library is distributed in the hope that it will be useful,
  13 ;   but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 ;   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 ;   GNU General Public License for more details.
  16 ;
  17 ;   You should have received a copy of the GNU General Public License
  18 ;   along with this library; see the file COPYING. If not, write to the
  19 ;   Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  20 ;   MA 02110-1301, USA.
  21 ;
  22 ;   As a special exception, if you link this library with other files,
  23 ;   some of which are compiled with SDCC, to produce an executable,
  24 ;   this library does not by itself cause the resulting executable to
  25 ;   be covered by the GNU General Public License. This exception does
  26 ;   not however invalidate any other reasons why the executable file
  27 ;   might be covered by the GNU General Public License.
  28 ;-------------------------------------------------------------------------
  29
  30         .module _mulint
  31
  32 ;--------------------------------------------------------
  33 ; exported symbols
  34 ;--------------------------------------------------------
  35         .globl __mulint_PARM_2
  36         .globl __mulint
  37
  38 ;--------------------------------------------------------
  39 ; overlayable function parameters in zero page
  40 ;--------------------------------------------------------
  41         .area   OSEG    (PAG, OVR)
  42 __mulint_PARM_2:
  43         .ds 2
  44
  45 ;--------------------------------------------------------
  46 ; local aliases
  47 ;--------------------------------------------------------
  48         .define tmp "___SDCC_m6502_ret2"
  49
  50 ;--------------------------------------------------------
  51 ; code
  52 ;--------------------------------------------------------
  53         .area CODE
  54
  55 __mulint:
  56         sta     *___SDCC_m6502_ret0
  57         stx     *___SDCC_m6502_ret1
  58         lda     #0
  59         sta     *tmp
  60         ldy     #16
  61         lsr     *___SDCC_m6502_ret1
  62         ror     *___SDCC_m6502_ret0
  63 next_bit:
  64         bcc     skip
  65         clc
  66         adc     *__mulint_PARM_2+0
  67         tax
  68         lda     *__mulint_PARM_2+1
  69         adc     *tmp
  70         sta     *tmp
  71         txa
  72 skip:
  73         ror     *tmp
  74         ror     a
  75         ror     *___SDCC_m6502_ret1
  76         ror     *___SDCC_m6502_ret0
  77         dey
  78         bne     next_bit
  79
  80         lda     *___SDCC_m6502_ret0
  81         ldx     *___SDCC_m6502_ret1
  82         rts