[Haskell-cafe] Data.Complex.magnitude slow?

[Henning Thielemann]

On Thu, 17 Jul 2008, stefan kersten wrote:

> i've attached an example program which seems to indicate that the magnitude 
> function from Data.Complex is very slow compared to a more naive 
> implementation (for Complex Float). on my machine (intel core2 duo, osx 10.4) 
> the CPU time using the library function is about 6-7 times as much as when 
> using the other function. any ideas what might be going on? any flaws in my 
> measurement code?

Complex.magnitude must prevent overflows, that is, if you just square 
1e200::Double you get an overflow, although the end result may be also 
around 1e200. I guess, that to this end Complex.magnitude will separate 
mantissa and exponent, but this is done via Integers, I'm afraid.