Hand coded factorial program in CIL assembly

fact.il

.assembly 'fact'
{
}

.namespace Factorial
{
  .class public Factorial
  {
    .method public static void Main(string[] argv)
    {
      .entrypoint

      ldarg.0
      ldlen

      brtrue MAIN
      ldstr "Usage: fact.exe n"
      call void class [mscorlib]System.Console::WriteLine(string)
      ret

      MAIN:
      ldarg.0
      ldc.i4.0
      ldelem.ref
      call int32 class [mscorlib]System.Convert::ToInt32(string)
      call int32 class Factorial.Factorial::Fact(int32)
      call void class [mscorlib]System.Console::WriteLine(int32)

      ret
    }

    .method private static int32 Fact(int32 n)
    {
      ldarg.0
      ldc.i4.0
      bgt NONZERO
      ldc.i4.1
      ret

      NONZERO:
      ldarg.0
      ldarg.0
      ldc.i4.1
      sub
      call int32 class Factorial.Factorial::Fact(int32)
      mul
      ret
    }
  }
}