sdcc/device/lib/z180/mul.s

   1 ;--------------------------------------------------------------------------
   2 ;  mul.s
   3 ;
   4 ;  Copyright (C) 2017-2021, 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 .hd64
  30 .area   _CODE
  31
  32 ; 16 x 16 -> 16 multiplication.
  33
  34 .globl  __mulint
  35
  36 __mulint:
  37         ;; 16-bit multiplication
  38         ;;
  39         ;; Entry conditions
  40         ;; hl = multiplicand
  41         ;; de = multiplier
  42         ;;
  43         ;; Exit conditions
  44         ;; hl = less significant word of product
  45         ;;
  46         ;; Register used: AF,BC,DE,HL
  47
  48 __mul16::
  49
  50         ; Swap lower bytes while also copying them.
  51         ld      c, e
  52         ld      b, h
  53         ld      h, d
  54         ld      d, l
  55
  56         mlt     bc
  57         mlt     hl
  58         mlt     de
  59
  60         ld      a, c
  61         add     a, l
  62         add     a, d
  63         ld      d, a
  64
  65         ret
  66