rom/utility/umult32.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Unsigned 32 bit multiplication function.
   6     Lang: english
   7 */
   8 #include "intern.h"
   9
  10 /*****************************************************************************
  11
  12     NAME */
  13 #include <proto/utility.h>
  14
  15         AROS_LH2(ULONG, UMult32,
  16
  17 /*  SYNOPSIS */
  18         AROS_LHA(ULONG        , arg1, D0),
  19         AROS_LHA(ULONG        , arg2, D1),
  20
  21 /*  LOCATION */
  22         struct UtilityBase *, UtilityBase, 24, Utility)
  23
  24 /*  FUNCTION
  25         Performs an unsigned 32-bit multiplication of arg1 * arg2 and
  26         returns a 32 bit value.
  27
  28     INPUTS
  29         arg1, arg2  -   32 bit unsigned longs
  30
  31     RESULT
  32         arg1 * arg2
  33
  34     NOTES
  35         This can perform the multiplication either using the machines
  36         native instructions (if they exist), or in software using a
  37         simple algorithm (three multiplications, two shifts and
  38         an addition.
  39
  40         The utility.library math functions are unlike all other utility
  41         functions in that they don't require the library base to be
  42         loaded in register A6, and they also save the values of the
  43         address registers A0/A1.
  44
  45         This function is mainly to support assembly programers, and is
  46         probably of limited use to higher-level language programmers.
  47
  48     EXAMPLE
  49
  50         LONG a = 352543;
  51         LONG b = 52464;
  52         LONG c = UMult32(a,b);
  53         c == 1315946768
  54
  55     BUGS
  56
  57     SEE ALSO
  58         SMult32(), UMult64(), SMult64()
  59
  60     INTERNALS
  61         May be handled by code in config/$(KERNEL), may not be...
  62
  63         It is for m68k-native...
  64
  65         To emulate this operation we are performing the operation:
  66
  67             (2^16 * a + b) * (2^16 * c + d)
  68           = 2^32 * ab + 2^16 * ad + 2^16 * bc + bd
  69           = 2^32 * ab + 2^16 ( ad + bc ) + bd
  70
  71         Now since the result is a 32-bit number, the 2^32 term will have
  72         no effect. (Since 2^32 > max (32-bit number).
  73
  74         Therefore:
  75         product = 2^16( ad + bc ) + bd
  76
  77     HISTORY
  78         29-10-95    digulla automatically created from
  79                             utility_lib.fd and clib/utility_protos.h
  80         18-08-96    iaint   Implemented as described above.
  81
  82 *****************************************************************************/
  83 {
  84     AROS_LIBFUNC_INIT
  85
  86     /* If we have native support for 32 * 32 -> 32, use that. */
  87
  88     return arg1 * arg2;
  89
  90 #if 0
  91     /* This is the equivalent to the emulating code,
  92         see also config/m68k-native/sumult32.s
  93     */
  94     UWORD a0, a1, b0, b1;
  95
  96     a1 = (arg1 >> 16) & 0xffff;
  97     a0 = arg1 & 0xffff;
  98     b1 = (arg2 >> 16) & 0xffff;
  99     b0 = arg2 & 0xffff;
 100
 101     return (((a0 * b1) + (a1 * b0)) << 16) + (b0 * a0);
 102 #endif
 103
 104     AROS_LIBFUNC_EXIT
 105 } /* UMult32 */