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Re: Fixed-point arithmetic library

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On 2/26/2012 7:59 PM, glen herrmannsfeldt wrote:
> Robert Klemme<shortcutter@googlemail.com>  wrote:
>
> (snip)
>>> I would quite like to represent some numbers in fixed point,
>>> and do arithmetic with them.
>
>> Fixed point math is susceptible to precision issues which can
>> be more severe than those of float and double: 0.01 * 0.2 ->  0.00
>
> In PL/I, if you multiply, you get the appropriate number if digits
> after the radix point.
>
> FIXED DECIMAL(3,2) times FIXED DECIMAL(2,1) generates a
> product of FIXED DECIMAL(5,3). If you force it to throw away
> low order digits, then, yes you can lose precision.

That is rather similar to how BigDecimal works.

import java.math.BigDecimal;

public class Fixed {
	public static void main(String[] args) {
		BigDecimal d1 = new BigDecimal("12.3");
		System.out.println(d1 + " " + d1.scale());
		BigDecimal d2 = new BigDecimal("4.56");
		System.out.println(d2 + " " + d2.scale());
		BigDecimal d3 = d1.multiply(d2);
		System.out.println(d3 + " " + d3.scale());
	}
}

12.3 1
4.56 2
56.088 3

Arne

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Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-22 21:39 +0000
  Re: Fixed-point arithmetic library Jan Burse <janburse@fastmail.fm> - 2012-02-22 22:59 +0100
    Re: Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-23 21:15 +0000
      Re: Fixed-point arithmetic library markspace <-@.> - 2012-02-23 13:53 -0800
      Re: Fixed-point arithmetic library Robert Klemme <shortcutter@googlemail.com> - 2012-02-23 23:21 +0100
      Re: Fixed-point arithmetic library Jan Burse <janburse@fastmail.fm> - 2012-02-24 00:02 +0100
  Re: Fixed-point arithmetic library Robert Klemme <shortcutter@googlemail.com> - 2012-02-22 23:13 +0100
    Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-22 14:59 -0800
      Re: Fixed-point arithmetic library Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-23 01:05 +0000
        Re: Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-23 21:21 +0000
          Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-23 13:49 -0800
      Re: Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-23 21:16 +0000
        Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-23 14:03 -0800
          Re: Fixed-point arithmetic library Lew <noone@lewscanon.com> - 2012-02-23 14:42 -0800
            Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-23 15:08 -0800
        Re: Fixed-point arithmetic library Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-23 23:05 +0000
    Re: Fixed-point arithmetic library glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-27 00:59 +0000
      Re: Fixed-point arithmetic library Arne Vajhøj <arne@vajhoej.dk> - 2012-02-26 20:50 -0500
        Re: Fixed-point arithmetic library Robert Klemme <shortcutter@googlemail.com> - 2012-02-27 07:32 +0100
          Re: Fixed-point arithmetic library Jan Burse <janburse@fastmail.fm> - 2012-02-27 13:46 +0100
  Re: Fixed-point arithmetic library Roedy Green <see_website@mindprod.com.invalid> - 2012-02-24 16:26 -0800

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