Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #12305

Re: Fixed-point arithmetic library

Show all headers | View raw

On Wed, 22 Feb 2012 21:39:20 +0000, Tom Anderson
<twic@urchin.earth.li> wrote, quoted or indirectly quoted someone who
said :

>These numbers will mostly not be more than a bilion, and will probably 
>never be more than a hundred billion. Some of them, i will need to 
>represent to eight decimal places

So long max 9,223,372,036,854,775,807  would be sufficient, except for
intermediate results?  I had a similar problem back in 1985
implementing a 32-bit forth on a 16-bit 8086 architecture.

If your results are still 64 bits, just collecting the low order bits
will work.

If you need 128 bits, you could do it like this for unsigned multiply.

split your two numbers into two 32 bit quantities

a = bc
d = ef


a * d =  c*f +  (b*f + c*e) >> 32 + (b*e) >> 64

In assembler this is easier since you get the high bits too as a
matter of course from a multiply.

If you don't need much, rolling your own based on the way you did it
in grade 4 (considering your numbers as base 2^32 numbers rather than
base 10). might be much easier than introducing a full library.

In the process I bested Knuth and came up with a more efficient
multiprecision division algorithm.
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
One of the most useful comments you can put in a program is 
"If you change this, remember to change ?XXX? too".
 

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Find similar

Thread

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

csiph-web