Re: [boost] [mpl][math] double accuracy

From: Andy Little (andy_at_[hidden])
Date: 2005-09-25 09:18:18

"Peder Holt" <peder.holt_at_[hidden]> wrote in message
news:4c1c5632050924115073d9251c_at_mail.gmail.com...
> What should we do about the accuracy of double_ operations?
>
> The implementation of plus,minus,times and divide mimics the behaviour
> of the runtime equivalent, double. This means that the mantissa is
> trunkated from 61 to 52 bit for every fundamental operation. The
> result of this, is that complex functions such as sine and exponential
> will differ from their runtime counterpart, unless a specialization is
> made for double_. The problem would disappear if we allow calculations
> with double_ to be more accurate than calculations with double. Is
> this a problem?

 There is neverending discussion on comp.lang.c++.mod regarding differences 
between runtime floats on various platforms. IMO this is an ideal opportunity to 
create a platform independent floating point type, IOW one with an exact length 
of  mantissa and exponent specified and with a consistent policy on rounding 
etc. I think this is how it is done in Java though the only link I can find 
is:http://www.concentric.net/~Ttwang/tech/javafloat.htm
Other question is ... What sort of rounding do you use?
Also ... I'm assuming it is simple enough to program the length of mantissa and 
exponent?.  By making them length adjustable you would be able to regain 
platform dependence via typedefs where required. thus providing the best of both 
worlds.

regards
Andy Little