Re: [boost] [MPL.Math] divergent results for double.cpp

From: Cromwell Enage (sponage_at_[hidden])
Date: 2005-10-25 14:32:37

--- Peder Holt wrote:
> I think the results are to be expected, if I
> understand them correctly.

Okay.

> 1. BOOST_MPL_MATH_DOUBLE uses built-in double
> arithmetics to extract the mantissa and the
> exponent at compile time.  Since the mantissa of
> double is limited to 52 bits, it uses rounding to
> get a best match.
> 
> 2. string_c_to_double on the other hand has ~60 bits
> available.

Should I then change big_integral_mantissa,
whole_part, and rational_part to account for the extra
bits?

> The only way to get these results to match, is to
> reintroduce the strict rounding to 52 bits on all
> double_'s but this would lead to a less-than-52-bit
> precision on mathematical functions such as sine.
> 
> We could of course also limit string_c_to_double's
> built in precision to 52 bits, but it seems such a
> waste to throw away the extra information :)

Indeed!

                              Cromwell D. Enage

                
__________________________________ 
Yahoo! FareChase: Search multiple travel sites in one click.
http://farechase.yahoo.com