SciMark2 Monte Carlo in F#

module SciMark2

module Random =
  let m = Array.create 17 0
  let mutable i = 4
  let mutable j = 16
  let mdig = 32
  let m1 = (1 <<< mdig - 2) + ((1 <<< mdig - 2) - 1)
  let m2 = 1 <<< mdig / 2
  let dm1 = 1.0 / float m1

  do
    let seed = 101010
    let jseed = min (abs seed) m1;
    let mutable jseed = if jseed &&& 1 = 0 then jseed - 1 else jseed
    let k0 = 9069 % m2
    let k1 = 9069 / m2
    let mutable j0 = jseed % m2
    let mutable j1 = jseed / m2
    for i=0 to 16 do
      jseed <- j0 * k0
      j1 <- (jseed / m2 + j0 * k1 + j1 * k0) % (m2 / 2)
      j0 <- jseed % m2
      m.[i] <- j0 + m2 * j1
    i <- 4
    j <- 16

  let inline NextDouble() =
    let mutable k = m.[i] - m.[j]
    if k < 0 then k <- k + m1
    m.[j] <- k
    i <- if i = 0 then 16 else i - 1
    j <- if j = 0 then 16 else j - 1
    dm1 * float k

module MonteCarlo =
  let flops n = 4 * n
  
  let exec n =
    let sqr x = x * x
    let mutable c = 0
    for i=1 to n do
      if sqr(Random.NextDouble()) + sqr(Random.NextDouble()) <= 1. then
        c <- c + 1
    4. * float c / float n

MonteCarlo.exec 100000000
|> printfn "%0.15f"