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Performance/Floating point

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Haskell Performance Resource

Constructs:
Data Types - Functions
Overloading - FFI - Arrays
Strings - Integers - I/O
Floating point - Concurrency
Modules - Monads

Techniques:
Strictness - Laziness
Avoiding space leaks
Accumulating parameter

Implementation-Specific:
GHC - nhc98 - Hugs
Yhc - JHC

Don't use Float

Floats (probably 32-bits) are almost always a bad idea, anyway, unless you Really Know What You Are Doing. Use Doubles. There's rarely a speed disadvantage—modern machines will use the same floating-point unit for both. With Doubles, you are much less likely to hang yourself with numerical errors.

One time when Float might be a good idea is if you have a lot of them, say a giant array of Floats. An unboxed array of Float (see Performance:Arrays) takes up half the space in the heap compared to an unboxed array of Double. However, boxed Floats might take up less space than boxed Doubles if you are on a 32-bit machine (on a 64-bit machine, a Float still takes up 64 bits).