Richard O'Keefe ha scritto:
On 5 Feb 2009, at 10:38 am, Manlio Perillo wrote:
I'm looking for an exact integer division that avoids overflows, if
possible.
What this sounds like to me is a request that the Prelude
function 'fromRational' should work well.
Just found that it actually works well, with Ratio Integer.
There is a specialized function in GHC.Float that does the right job.
[...]
You'd actually use scaleFloat; if the difference sp-sq is outside
the range of Int the answer is going to be a signed zero or a signed
infinity anyway. decodeIntegerAsFloat would sit very well in the
RealFloat class alongside its model, decodeFloat. It has other uses.
For example, you can use it to compute logarithms of Integers with
much less worry about overflow.
By the way, in GHC.Float there is a (private):
-- Compute the (floor of the) log of i in base b.
-- Simplest way would be just divide i by b until it's smaller then b,
-- but that would be very slow! We are just slightly more clever.
integerLogBase :: Integer -> Integer -> Int
Regards Manlio Perillo
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