Re: [boost] Large Integer Library

Subject: Re: [boost] Large Integer Library
From: John Maddock (boost.regex_at_[hidden])
Date: 2012-06-30 13:16:29

> (All taken from
> http://svn.boost.org/svn/boost/sandbox/big_number/libs/multiprecision/doc/html/boost_multiprecision/intro.html
> )
>
> * "Fixed at compile time values, for example 50 decimal digits"
>
> Boost.LargeInt is designed to stick-together two existing integer or
> integer-
> like types, so although also being fixed at compile-time, it is fixed to a
> number of binary-bits rather than decimal digits.

Please note the "for example" part.

Fixed precision integers are fixed to the number of bits in 
Boost.Multiprecision the same as yours are.

> * "A header-only Boost license version is always available (if somewhat
> slower)."
>
> Boost.LargeInt is solely header and template based, and so is fully
> compatible
> with, Boost License v1.0 without restriction.  So, it performs as 
> optimally
> as
> possible regardless of licensing requirements.

So no difference then?  ;-)

> * "You have to be careful to cast the result of an expression to the 
> actual
>   number type when passing an expression to a template function"
>
> The results of all arithmetic operators in Boost.LargeInt are themselves
> boost::large_int::large_int based types, and so their use is fully
> transparent.

You can turn expression templates off in the multiprecision lib, in which 
case it behaves as yours does - in fact the expression templates are turned 
off for the fixed precision integer part, as it adds nothing there.

>* All logical, arithmetic and bitwise operators in Boost.LargeInt
>  have constant, O(1) complexity; except for multiplication ('*'),
>  division ('/') and modulus ('%') which are O(n) on the number
>  of bits in the respective large_int type.  Hence support for non
>  power-of-2 large_ints of 96bits, 160bits or otherwise may
>  be used to improve calculation performance.

Congratulations, the Fields medal is clearly on it's way!

Seriously, you might want to think again on those complexities...

>* All boost::large_int::large_int based types are comparable
>  against long-type literal values.  (These get an automatic
>  promotion to a boost::large_int equivalent to service said
>  comparison.)

Likewise the multiprecision lib (in fact promotion to the extended type 
first isn't strictly necessary - you can do things more efficiently than 
that).

Cheers, John.