FastMathBenchmarks.cs

using System;
using BenchmarkDotNet.Running;
using BenchmarkDotNet.Attributes;

class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);
}

public class Case2_DivToMul
{
    [Benchmark(Baseline = true)]
    [Arguments(MathF.PI, 100)]
    public float Old(float value, int iterations)
    {
        for (int i = 0; i < iterations; i++)
            value = value / 10;
        return value;
    }

    [Benchmark]
    [Arguments(MathF.PI, 100)]
    public float New(float value, int iterations)
    {
        for (int i = 0; i < iterations; i++)
            value = value * 0.1f; 
        return value;
    }
}

public class Case1_Fmadd
{
    [Benchmark(Baseline = true)]
    [Arguments(42.51f, 1/3f, 100)]
    public float Old(float a, float b, int iterations)
    {
        float z = 1f;
        for (int i = 0; i < iterations; i++)
            z = z * a + b;
        return z;
    }

    [Benchmark]
    [Arguments(42.51f, 1 / 3f, 100)]
    public float New(float a, float b, int iterations)
    {
        float z = 1f;
        for (int i = 0; i < iterations; i++)
            z = MathF.FusedMultiplyAdd(z, a, b); // let's pretend JIT generates it
        return z;
    }
}

public class Case5
{
    [Benchmark(Baseline = true)]
    [Arguments(42.51f, 1 / 3f, 100)]
    public float Old(float a, float b, int iterations)
    {
        float z = 1f;
        for (int i = 0; i < iterations; i++)
            z = (z * a) + (z * b);
        return z;
    }

    [Benchmark]
    [Arguments(42.51f, 1 / 3f, 100)]
    public float New(float a, float b, int iterations)
    {
        float z = 1f;
        for (int i = 0; i < iterations; i++)
            z = z * (a + b);
        return z;
    }
}