array_performance.fs

open System.Diagnostics

let sum1 (a:array<_>) total =
    total := 0
    for i = 0 to a.Length-1 do
        total := !total + a.[i]
    !total

let sum2 (a:array<_>) total =
    total := 0
    let mutable i = 0
    while i < a.Length do
        total := !total + a.[i]
        i <- i + 1
    !total

let sum3 (a:array<_>) total =
    total := 0
    let rec iterate i =
        if i < a.Length then
            total := !total + a.[i]
            iterate (i+1)
    iterate 0
    !total

let t f a =
    let sw = Stopwatch.StartNew ()
    let total = ref 0
    if f a total <> 10000000 then
        failwith "boom!"
    sw.ElapsedMilliseconds


[<EntryPoint>]
let main argv = 
    let data = Array.zeroCreate 10000000
    for i = 0 to data.Length-1 do
        data.[i] <- 1

    let z = t sum1 data
    let z = t sum2 data
    let z = t sum3 data

    let mutable _1 = 0L
    let mutable _2 = 0L
    let mutable _3 = 0L

    for i = 1 to 5 do
        for i = 1 to 50 do
            _1 <- _1 + t sum1 data
            _2 <- _2 + t sum2 data
            _3 <- _3 + t sum3 data

        printfn "%d\t%d\t%d" _1 _2 _3
    0