C# `float` vs `double`: Performance Considerations

In C# there're 3 floating-point numeric types:

• Single precision 32-bit/4-byte float
• Double precision 64-bit/8-byte double
• 128-bit/16-byte decimal

As long as you don't need extended precision, will 32-bit floats perform better? Intuition suggests that smaller types will be faster.

I tested this hypothesis with Mandelbrot calculation. I.e. I have implemented the same algorithm twice, the only difference being different variable types:

...

public struct Complex
{
  public double Real { get; set; }
  public double Imaginary { get; set; } 
  ...
}

...

public struct ComplexF
{
  public float Real { get; set; }
  public float Imaginary { get; set; }
  ...
}

...

// Part of calculation
private static int[] MandelbrotF()
{
  var output = new int[Height * Width];
  for (int h = 0, idx = 0; h < Height; h++, idx += Width)
  {
    float cy = MinYf + h * ScaleYf;
    for (int w = 0; w < Width; w++)
    {
      float cx = MinXf + w * ScaleXf;
      output[idx + w] = Mandelbrot_0F(new ComplexF(cx, cy));
    }
  }
  return output;
}
..

Turns out, float is slower. Tested it many times on different machines and it was always behind double.

dotnet run -c Release

Platform	Precision	Avg Time (ms)	StdDev (%)	Sum
Apple M1 Pro	double	392.70	0.14	78513425
Apple M1 Pro	float	395.49	0.38	78520223
Intel® Core™ i5-8257U CPU @ 1.40GHz	double	355.99	13.13	78513425
Intel® Core™ i5-8257U CPU @ 1.40GHz	float	372.59	1.13	78520223
AMD 5900x	double	185.80	0.97	78513425
AMD 5900x	float	207.49	0.75	78520223

dotnet build -c Release

Platform	Precision	Avg Time (ms)	StdDev (%)	Sum
Apple M1 Pro	double	392.42	0.11	78513425
Apple M1 Pro	float	395.35	0.13	78520223
Intel® Core™ i5-8257U CPU @ 1.40GHz	double	327.30	3.82	78513425
Intel® Core™ i5-8257U CPU @ 1.40GHz	float	370.90	1.48	78520223

• Tested with .NET 7.0.307
• Sum column shows how different types produced different results (summarising resulting array elements)