Andras Erdei wrote:
On Mon, 7 Mar 2005 17:50:48 -0700, Jonathan Turkanis <technews@kangaroologic.com> wrote:
I can't tell what template parameters you think rational should have.
(it is because i don't know myself :O)
Okay.
i think we need two parameters: one for specifying the precision, and one for specifying the variant to use
But this leaves out the int_type; users must be able to write rational<big_int> or similarly for any UDT which supports the euclidean algorithm.
the problems:
1. if we specify the precision as an integer, e.g. rational<1000> meaning a rational with numerator range (-1000,1000) and denominator range (1,1000), then we restrict the possible underlying types to the integer type used as the template parameter (and smaller)
a possible workaround is to specify the log of the limits instead, so e.g. rational<31> would mean (-2^31,2^31) and (1,2^31) -- this is less flexible, than the above one, but i can't come up with anything better
I believe precision should be specified by supplying an appropriate type as the int type, e.g., restricted_int<1000>.
2. i don't know how can we implement the selection of UDTs: let's say i have implemented a modular arithmetic bigint type, with up to a few hundred bits of precision -- how can i tell rational that it can select this as the underlying type?
It has to be specified as a template parameter. Even if we specified a whole range of types, including big_int, to serve as the underlying type depending on the specified precision, an arbitrary user-supplied type would never be selected.
<snip>
The above declaration was based on the assumption that multiple rounding policies should be supported. If there's only one way to round, then rounding can be merged into the checking policy.
i don't see how this depends on having more than one kind of rounding: either you round, or you check, cannot do both at the same time -- do i miss something?
Okay, I see. The various checking policies, such as assert_check, etc., are just rounding policies which alert the used that something has gone wrong as soon as it is determined that rounding is required. Good. So rational should look like: template<typename Elem, typename Rounding = use_default> class rational; On top of this could be built a restricted precision rational class. Jonathan