Stephane Bortzmeyer wrote:
But he can write one in PostgreSQL quite easily. Rational numbers are always the first exercice in CS courses about Abstract Data Types :-)
It's a little tricky to get good performance for all the operations:
The addition and subtraction operations are complex. They will require approximately two gcd operations, 3 divisions, 3 multiplications and an addition on the underlying integer type. The multiplication and division operations require two gcd operations, two multiplications, and four divisions. The comparison operations require two gcd operations, two multiplications, four divisions and a comparison in the worst case. On the assumption that IntType comparisons are the cheapest of these operations (and that comparisons agains zero may be cheaper still), these operations have a number of special case optimisations to reduce the overhead where possible. In particular, equality and inequality tests are only as expensive as two of the equivalent tests on the underlying integer type.
(From the Booost rational package - http://www.boost.org/libs/ rational/rational.html)
I'd try to link to an existing library that provides rationals, or model my code closely after one.
- John D. Burger MITRE
