sdcc/device/lib/z80/mul.s

   1 ;--------------------------------------------------------------------------
   2 ;  mul.s
   3 ;
   4 ;  Copyright (C) 2000, Michael Hope
   5 ;  Copyright (C) 2021, Philipp Klaus Krause
   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 mul
  31         .optsdcc -mz80 sdcccall(1)
  32
  33 .area   _CODE
  34
  35 .globl  __mulint
  36
  37 __mulint:
  38         ld      c, l
  39         ld      b, h
  40
  41         ;; 16-bit multiplication
  42         ;;
  43         ;; Entry conditions
  44         ;; bc = multiplicand
  45         ;; de = multiplier
  46         ;;
  47         ;; Exit conditions
  48         ;; de = less significant word of product
  49         ;;
  50         ;; Register used: AF,BC,DE,HL
  51 __mul16::
  52         xor     a,a
  53         ld      l,a
  54         or      a,b
  55         ld      b,#16
  56
  57         ;; Optimise for the case when this side has 8 bits of data or
  58         ;; less.  This is often the case with support address calls.
  59         jr      NZ,2$
  60         ld      b,#8
  61         ld      a,c
  62 1$:
  63         ;; Taken from z88dk, which originally borrowed from the
  64         ;; Spectrum rom.
  65         add     hl,hl
  66 2$:
  67         rl      c
  68         rla                     ;DLE 27/11/98
  69         jr      NC,3$
  70         add     hl,de
  71 3$:
  72         djnz    1$
  73         ex      de, hl
  74         ret
  75