- class (C a, Ord a) => C a where
- roundSimple :: (C a, C b) => a -> b
- fastSplitFraction :: (RealFrac a, C a, C b) => (a -> Int) -> (Int -> a) -> a -> (b, a)
- fixSplitFraction :: (C a, C b, Ord a) => (b, a) -> (b, a)
- fastFraction :: (RealFrac a, C a) => (a -> a) -> a -> a
- preludeFraction :: (RealFrac a, C a) => a -> a
- fixFraction :: (C a, Ord a) => a -> a
- splitFractionInt :: (C a, Ord a) => (a -> Int) -> (Int -> a) -> a -> (Int, a)
- floorInt :: (C a, Ord a) => (a -> Int) -> (Int -> a) -> a -> Int
- ceilingInt :: (C a, Ord a) => (a -> Int) -> (Int -> a) -> a -> Int
- roundInt :: (C a, Ord a) => (a -> Int) -> (Int -> a) -> a -> Int
- roundSimpleInt :: (C a, C a, Ord a) => (a -> Int) -> (Int -> a) -> a -> Int
- approxRational :: (C a, C a) => a -> a -> Rational
- powersOfTwo :: C a => [a]
- pairsOfPowersOfTwo :: (C a, C b) => [(a, b)]
- genericFloor :: (Ord a, C a, C b) => a -> b
- genericCeiling :: (Ord a, C a, C b) => a -> b
- genericTruncate :: (Ord a, C a, C b) => a -> b
- genericRound :: (Ord a, C a, C b) => a -> b
- genericFraction :: (Ord a, C a) => a -> a
- genericSplitFraction :: (Ord a, C a, C b) => a -> (b, a)
- genericPosFloor :: (Ord a, C a, C b) => a -> b
- genericPosCeiling :: (Ord a, C a, C b) => a -> b
- genericHalfPosFloorDigits :: (Ord a, C a, C b) => a -> ((a, b), [Bool])
- genericPosRound :: (Ord a, C a, C b) => a -> b
- genericPosFraction :: (Ord a, C a) => a -> a
- genericPosSplitFraction :: (Ord a, C a, C b) => a -> (b, a)
- decisionPosFraction :: (C a, C a) => a -> a
- decisionPosFractionSqrTime :: (C a, C a) => a -> a
There are probably more laws, but some laws are
splitFraction x === (fromInteger (floor x), fraction x) fromInteger (floor x) + fraction x === x floor x <= x x < floor x + 1 ceiling x - 1 < x x <= ceiling x 0 <= fraction x fraction x < 1
- ceiling x === floor (-x) truncate x === signum x * floor (abs x) ceiling (toRational x) === ceiling x :: Integer truncate (toRational x) === truncate x :: Integer floor (toRational x) === floor x :: Integer
The new function
fraction doesn't return the integer part of the number.
This also removes a type ambiguity if the integer part is not needed.
Many people will associate rounding with fractional numbers,
and thus they are surprised about the superclass being
The reason is that all of these methods can be defined
exclusively with functions from
The implementations of
genericFloor and other functions demonstrate that.
They implement power-of-two-algorithms
like the one for finding the number of digits of an
in FixedPoint-fractions module.
They are even reasonably efficient.
I am still uncertain whether it was a good idea
to add instances for
Integer and friends,
fraction on an integer may well indicate a bug.
The rounding functions are just the identity function
fraction is constant zero.
However, I decided to associate our class with
Ring rather than
after I found myself using repeated subtraction and testing
rather than just calling
just in order to get the constraint
(Ring a, Ord a)
that was more general than
For the results of the rounding functions
we have chosen the constraint
Ring instead of
since this is more flexible to use,
but it still signals to the user that only integral numbers can be returned.
This is so, because the plain
Ring class only provides
one and operations that allow to reach all natural numbers but not more.
As an aside, let me note the similarities
splitFraction x and
divMod x 1 (if that were defined).
In particular, it might make sense to unify the rounding modes somehow.
The new methods
They always round to
This means that the fraction is always non-negative and
is always smaller than 1.
This is more useful in practice and
can be generalised to more than real numbers.
T denominator type
T can provide
e.g. fractions of polynomials.
Ring constraint for the ''integral'' part of
is too weak in order to generate polynomials.
After all, I am uncertain whether this would be useful or not.
We might also add a round method, that rounds 0.5 always up or always down. This is much more efficient in inner loops and is acceptable or even preferable for many applications.
This function rounds to the closest integer.
fraction x == 0.5 it rounds away from zero.
This function is not the result of an ingenious mathematical insight,
but is simply a kind of rounding that is the fastest
on IEEE floating point architectures.
TODO: Should be moved to a continued fraction module.
generic implementation of round functions
The generic rounding functions need a number of operations proportional to the number of binary digits of the integer portion. If operations like multiplication with two and comparison need time proportional to the number of binary digits, then the overall rounding requires quadratic time.
Needs linear time with respect to the number of digits.
This and other functions using OrderDecision
floor where argument and result are the same
may be moved to a new module.