Re: precise floats

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Matthew said

<<Actually, it's not necessary anyway.  The compiler will reject the
declaration

   type Fail_If_Not_Precise_Enough is digits N;

if it can't give you at least N digits.
>>


The whole idea of requesting the precision you need at this level of
detail (number of decimal digits) is to me a bit bogus. It sounds good
if you are not doing serious numerical analysis, but in real life the
idea that you sit down with your program, figure out you need 12 digits,
then ask for it, and hope to get it, is very rarely the case.

Indeed there are quite a few algorithms where even if you could do this
kind of analysis, it would not work, because these algorithms fail if
you have too much precision. In general extra unwanted precision can
be quite an enemy to efficient floating-point code.

Especially in these days where virtually all machines use IEEE float formats,
even if they (increasingly, GRRR) don't provide 100% full IEEE arithmetic
semantics, the whole business about taking a high level abstract view of
precision requirements is dubious.