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Subject: Re: [boost] [mp_int] new release
From: Kevin Sopp (baraclese_at_[hidden])
Date: 2008-10-09 19:21:54

> First there is no A % B operation which is const (boost::rational complained
> as it tries to do a mod operation on a const int_type.) I added one and got
> past this.

How does the function you added look like? I'm not sure I understand
why you would want to do a mod operation on a constant type.
a = b % c; // b and c are constant
a %= b; // b is constant
Both are supported.

> During the normalization step of boost::rational the numerator and
> denominator are normalized by the gcd of the two. In one case I was testing
> the %= operator of mp_int<> was causing an infinite loop in the
> boost::math::gcd call. I made an attempt at a fix (though I didn't really
> spend much time on it.. so I'm not sure what if any side-effects)
> ...
> The case I had fail was when normalizing (-16384)/(16384). (-1/1). So it was
> infinite looping on boost::math::gcd( mp_int<>( -16384 ), mp_int<>( 16384 )
> );

Is it possible for Boost.Rational to delegate to the mp_math::gcd
(which should be faster than math::gcd)? mp_math::gcd handles mixed
negative/positive numbers just fine.

> double rational_cast( const boost::rational< boost::mp_math::mp_int<> >& src
> )
> {
> ...
> }

I cannot confirm that you hit a bug here. While trying to see what is
going on I discovered an unrelated bug in the to_string conversion
using decimal output which happens in rare cases (it will swallow a
midnumber zero when it lies on a certain boundary). Can you provide me
with some starting values?

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