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F# imperative performance
f#c#

Hello all,

I've been experimenting with f# and liked its syntax and powerful type inference mechanism. But I have some question about its performance while writing in imperative style, namely about 'for' loop. My code:

open System

let mutable arr = [|1..100000|]

let dt1 = DateTime.Now;

let func_calc arrayValue =

for i = 0 to 99999 do

arr.[ i ] := arrayValue

for i = 0 to 1000 do

func_calc i

let dt2 = DateTime.Now;

let ts1 = dt2 - dt1;

printfn "%f" ts1.TotalMilliseconds

System.Console.Read();

This code fulfills in 3500 ms while similar code written in c# fulfills in about 500 ms. Is this ok? Why?

.

The JIT in the CLR is very sensitive to the exact format of iterating over an array regarding when it can optimize away the index boundary checks. Can you try using the form

for i in 0 to arrayValue.Length - 1 do

and check the result? (Also ensure you are in 'release' mode or compiling with optimizations enabled.)

By on 11/4/2009 12:34 PM ()

Thank you, with your recommendations code completes in 900ms. Code modification was

...

let arrUpperBound = arr.Length - 1

....

for i = 0 to arrUpperBound do

...

By on 11/4/2009 12:49 PM ()

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