C#编译器不限制浮点文字的小数部分的位数

Question

这仅用于学术目的.

我注意到对于整数文字,我们可以声明 18446744073709551615哪个是2^64-1或ulong.MaxValue.定义大于此值会产生编译时错误.

对于浮点文字,我们可以使用整数部分声明它们999...999(9重复308次).再次使用更多数字声明整数部分会产生编译时错误.我感兴趣的一件事是编译器似乎允许我们指定小数部分无限数字的位数.实际上,小数部分的无限数字位数没有意义.

问题:

1. 是否有一个常量表示C#编译器内部定义的最大位数,用于浮点数的小数部分？

2. 如果存在这样的常量,当用户指定超出其限制的小数部分时,为什么C#编译器不会抛出编译时错误？

最小工作示例1

namespace FloatingPoint
{
    class Program
    {
        static void Main(string[] args)
        {
            const ulong @ulong = 18446744073709551615;
            const double @double = 99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;

        }
    }
}

最小工作示例2

using System;

namespace FloatingPoint
{
    class Program
    {
        static void Main(string[] args)
        {

            const double x01 = 0.9;
            const double x02 = 0.99;
            const double x03 = 0.999;
            const double x04 = 0.9999;

            const double x05 = 0.99999;
            const double x06 = 0.999999;
            const double x07 = 0.9999999;
            const double x08 = 0.99999999;

            const double x09 = 0.999999999;
            const double x10 = 0.9999999999;
            const double x11 = 0.99999999999;
            const double x12 = 0.999999999999;

            const double x13 = 0.9999999999999;
            const double x14 = 0.99999999999999;
            const double x15 = 0.999999999999999;
            const double x16 = 0.9999999999999999;

            const double x17 = 0.99999999999999999;
            const double x18 = 0.999999999999999999;
            const double x19 = 0.9999999999999999999;
            const double x20 = 0.99999999999999999999;

            Console.WriteLine(x01);
            Console.WriteLine(x02);
            Console.WriteLine(x03);
            Console.WriteLine(x04);
            Console.WriteLine(x05);
            Console.WriteLine(x06);
            Console.WriteLine(x07);
            Console.WriteLine(x08);
            Console.WriteLine(x09);
            Console.WriteLine(x10);
            Console.WriteLine(x11);
            Console.WriteLine(x12);
            Console.WriteLine(x13);
            Console.WriteLine(x14);
            Console.WriteLine(x15);
            Console.WriteLine(x16);
            Console.WriteLine(x17);
            Console.WriteLine(x18);
            Console.WriteLine(x19);
            Console.WriteLine(x20);

        }
    }
}

/* output:

0.9
0.99
0.999
0.9999
0.99999
0.999999
0.9999999
0.99999999
0.999999999
0.9999999999
0.99999999999
0.999999999999
0.9999999999999
0.99999999999999
0.999999999999999
1
1
1
1
1
*/

IL:

.method private hidebysig static void  Main(string[] args) cil managed
{
  .entrypoint
  // Code size       302 (0x12e)
  .maxstack  1
  IL_0000:  nop
  IL_0001:  ldc.r8     0.90000000000000002
  IL_000a:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_000f:  nop
  IL_0010:  ldc.r8     0.98999999999999999
  IL_0019:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_001e:  nop
  IL_001f:  ldc.r8     0.999
  IL_0028:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_002d:  nop
  IL_002e:  ldc.r8     0.99990000000000001
  IL_0037:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_003c:  nop
  IL_003d:  ldc.r8     0.99999000000000005
  IL_0046:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_004b:  nop
  IL_004c:  ldc.r8     0.99999899999999997
  IL_0055:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_005a:  nop
  IL_005b:  ldc.r8     0.99999990000000005
  IL_0064:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_0069:  nop
  IL_006a:  ldc.r8     0.99999998999999995
  IL_0073:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_0078:  nop
  IL_0079:  ldc.r8     0.99999999900000003
  IL_0082:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_0087:  nop
  IL_0088:  ldc.r8     0.99999999989999999
  IL_0091:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_0096:  nop
  IL_0097:  ldc.r8     0.99999999999
  IL_00a0:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00a5:  nop
  IL_00a6:  ldc.r8     0.99999999999900002
  IL_00af:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00b4:  nop
  IL_00b5:  ldc.r8     0.99999999999989997
  IL_00be:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00c3:  nop
  IL_00c4:  ldc.r8     0.99999999999999001
  IL_00cd:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00d2:  nop
  IL_00d3:  ldc.r8     0.999999999999999
  IL_00dc:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00e1:  nop
  IL_00e2:  ldc.r8     0.99999999999999989
  IL_00eb:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00f0:  nop
  IL_00f1:  ldc.r8     1.
  IL_00fa:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_00ff:  nop
  IL_0100:  ldc.r8     1.
  IL_0109:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_010e:  nop
  IL_010f:  ldc.r8     1.
  IL_0118:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_011d:  nop
  IL_011e:  ldc.r8     1.
  IL_0127:  call       void [mscorlib]System.Console::WriteLine(float64)
  IL_012c:  nop
  IL_012d:  ret
} // end of method Program::Main

Answer 1

1. 是的，但它们不是十进制数字
2. 当规范是十进制并且表示是二进制时，超出精确表示它们的能力的小数部分的规范是很容易的。 0.3已经需要近似。