sdcc/device/lib/z80n/mul.s

   1 ;--------------------------------------------------------------------------
   2 ;  mul.s
   3 ;
   4 ;  Copyright (C) 2000, Michael Hope
   5 ;  Copyright (C) 2021, Philipp Klaus Krause
   6 ;  Copyright (C) 2024, Peter Ped Helcmanovsky
   7 ;  Copyright (C) 2024, Janko Stamenović
   8 ;
   9 ;  This library is free software; you can redistribute it and/or modify it
  10 ;  under the terms of the GNU General Public License as published by the
  11 ;  Free Software Foundation; either version 2, or (at your option) any
  12 ;  later version.
  13 ;
  14 ;  This library is distributed in the hope that it will be useful,
  15 ;  but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 ;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  17 ;  GNU General Public License for more details.
  18 ;
  19 ;  You should have received a copy of the GNU General Public License
  20 ;  along with this library; see the file COPYING. If not, write to the
  21 ;  Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  22 ;   MA 02110-1301, USA.
  23 ;
  24 ;  As a special exception, if you link this library with other files,
  25 ;  some of which are compiled with SDCC, to produce an executable,
  26 ;  this library does not by itself cause the resulting executable to
  27 ;  be covered by the GNU General Public License. This exception does
  28 ;  not however invalidate any other reasons why the executable file
  29 ;   might be covered by the GNU General Public License.
  30 ;--------------------------------------------------------------------------
  31
  32         .zxn
  33
  34 .area   _CODE
  35
  36 .globl  __mulint
  37
  38 __mulint:
  39 __mul16_HL_DE_to_DE::
  40         ;; unsigned _mulint (unsigned m, unsigned n) __sdcccall(1);
  41         ;;
  42         ;; 16-bit multiplication
  43         ;;
  44         ;; Entry conditions
  45         ;; hl = multiplicand
  46         ;; de = multiplier
  47         ;;
  48         ;; Exit conditions
  49         ;; de = less significant word of product
  50         ;;
  51         ;; Registers used: AF, C,DE,HL
  52         ;
  53         ; Goal:  DE :=  H_0 L_0  *  D_0 E_0
  54         ; (_0 inital content of the registers,
  55         ;  16-bit register pairs contain
  56         ;  16-bit values to be multiplied.)
  57         ;
  58         ; see also: mul_16_16_16_AE (CC0)
  59         ld c, e
  60         ld e, l
  61         mlt de   ;
  62         ld a, e  ; A =  LOWBYTE( D_O*L_0 )
  63         ld e, c
  64         ld d, h
  65         mlt de   ;
  66         add a, e ; A += LOWBYTE( E_0*H_0 )
  67         ld e, c
  68         ld d, l
  69         mlt de   ; DE = E_0*L_0
  70         add a, d ; A += HIGHBYTE( E_0*L_0 )
  71         ld d, a
  72         ; total: 64T to here
  73         ; D = the upper product byte, summed
  74         ; E = LOW( E_0*L_0 )
  75         ret
  76