sdcc/device/lib/mos6502/_mullong.s

   1 ;-------------------------------------------------------------------------
   2 ;   _mullong.s - routine for multiplication of 32 bit (unsigned) long
   3 ;
   4 ;   Copyright (C) 1998, 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 _mullong
  31
  32 ;--------------------------------------------------------
  33 ; exported symbols
  34 ;--------------------------------------------------------
  35         .globl __mullong_PARM_2
  36         .globl __mullong_PARM_1
  37         .globl __mullong
  38
  39 ;--------------------------------------------------------
  40 ; overlayable function parameters in zero page
  41 ;--------------------------------------------------------
  42         .area   OSEG    (PAG, OVR)
  43 __mullong_PARM_1:
  44         .ds 4
  45 __mullong_PARM_2:
  46         .ds 4
  47
  48 ;--------------------------------------------------------
  49 ; local aliases
  50 ;--------------------------------------------------------
  51         .define tmp  "___SDCC_m6502_ret4"
  52         .define res0 "__mullong_PARM_1+0"
  53         .define res1 "__mullong_PARM_1+1"
  54         .define res2 "___SDCC_m6502_ret2"
  55         .define res3 "___SDCC_m6502_ret3"
  56
  57 ;--------------------------------------------------------
  58 ; code
  59 ;--------------------------------------------------------
  60         .area CODE
  61
  62 __mullong:
  63
  64         ldx     *__mullong_PARM_1+3
  65         stx     *res3
  66         ldx     *__mullong_PARM_1+2
  67         stx     *res2
  68 ;        ldx    *__mullong_PARM_1+1
  69 ;        stx    *res1
  70 ;        ldx    *__mullong_PARM_1+0
  71 ;        stx    *res0
  72
  73         lda     #0
  74         sta     *tmp+2
  75         sta     *tmp+1
  76         sta     *tmp+0
  77
  78         ldy     #32
  79 next_bit:
  80         lsr     *tmp+2
  81         ror     *tmp+1
  82         ror     *tmp+0
  83         ror     a
  84         ror     *res3
  85         ror     *res2
  86         ror     *res1
  87         ror     *res0
  88         bcc     skip
  89         clc
  90         adc     *__mullong_PARM_2+0
  91         tax
  92         lda     *__mullong_PARM_2+1
  93         adc     *tmp+0
  94         sta     *tmp+0
  95         lda     *__mullong_PARM_2+2
  96         adc     *tmp+1
  97         sta     *tmp+1
  98         lda     *__mullong_PARM_2+3
  99         adc     *tmp+2
 100         sta     *tmp+2
 101         txa
 102 skip:
 103         dey
 104         bpl     next_bit
 105         ldx     *res1
 106         lda     *res0
 107         rts