FastVsSlow.fs

open System
open BenchmarkDotNet.Attributes
open BenchmarkDotNet.Running
open BenchmarkDotNet.Diagnosers

[<HardwareCounters(HardwareCounter.BranchMispredictions, HardwareCounter.CacheMisses)>]
[<DisassemblyDiagnoser(printSource = true, exportHtml = true)>]
type Benchmarks () =

    let rng = Random 123
    let arraySize = 1_000

    let lookupValues =
        [| for _ = 1 to arraySize do rng.Next (0, 100) |]

    let arrayOrderedFast (a: array<int>) =
        let mutable result = 0
        let mutable i = 0
        while i < a.Length - 1 do
            result <- a[i]
            i <- i + 1
        result

    [<Benchmark>]
    member _.ArrayOrderedSlow () =
        let mutable result = 0
        let mutable i = 0
        while i < lookupValues.Length - 1 do
            result <- lookupValues[i]
            i <- i + 1
        result

    [<Benchmark>]
    member _.ArrayOrderedFast () =
        arrayOrderedFast lookupValues