When Generating Primes in F#, why is the “Sieve of Erosthenes” so slow in this particular implementatIon?

Question

IE,

What am I doing wrong here? Does it have to to with lists, sequences and arrays and the way the limitations work?

So here is the setup: I\'m trying to g

Answer 1

Based on my code here: stackoverflow.com/a/8371684/124259

Gets the first 1 million primes in 22 milliseconds in fsi - a significant part is probably compiling the code at this point.

#time "on"

let limit = 1000000
//returns an array of all the primes up to limit
let table =
    let table = Array.create limit true //use bools in the table to save on memory
    let tlimit = int (sqrt (float limit)) //max test no for table, ints should be fine
    let mutable curfactor = 1;
    while curfactor < tlimit-2 do
        curfactor <- curfactor+2
        if table.[curfactor]  then //simple optimisation
            let mutable v = curfactor*2
            while v < limit do
                table.[v] <- false
                v <- v + curfactor
    let out = Array.create (100000) 0 //this needs to be greater than pi(limit)
    let mutable idx = 1
    out.[0]<-2
    let mutable curx=1
    while curx < limit-2 do
        curx <- curx + 2
        if table.[curx] then
            out.[idx]<-curx
            idx <- idx+1
    out