如何解析有符号零? [英] How to parse signed zero?

问题描述

是否可以解析带符号的零? 我尝试了几种方法，但没有人给出正确的结果:

Is it possible to parse signed zero? I tried several approaches but no one gives the proper result:

float test1 = Convert.ToSingle("-0.0");
float test2 = float.Parse("-0.0");
float test3;
float.TryParse("-0.0", out test3);

如果我使用直接初始化的值就可以了:

If I use the value directly initialized it is just fine:

float test4 = -0.0f;

所以问题似乎出在c#的解析过程中.我希望有人能告诉您是否有某些选择或解决方法.

So the problem seems to be in the parsing procedures of c#. I hope somebody could tell if there is some option or workaround for that.

只能通过转换为二进制来看到区别:

The difference could only be seen by converting to binary:

var bin= BitConverter.GetBytes(test4);

推荐答案

我认为没有办法强制float.Parse(或Convert.ToSingle)尊重负零.它就是这样工作的(在这种情况下忽略符号).因此，您必须检查一下自己，例如:

I think there is no way to force float.Parse (or Convert.ToSingle) to respect negative zero. It just works like this (ignores sign in this case). So you have to check that yourself, for example:

string target = "-0.0";            
float result = float.Parse(target, CultureInfo.InvariantCulture);
if (result == 0f && target.TrimStart().StartsWith("-"))
    result = -0f;

如果我们查看源代码对于coreclr，我们将看到(跳过所有不相关的部分):

If we look at source code for coreclr, we'll see (skipping all irrelevant parts):

private static bool NumberBufferToDouble(ref NumberBuffer number, ref double value)
{
    double d = NumberToDouble(ref number);
    uint e = DoubleHelper.Exponent(d);
    ulong m = DoubleHelper.Mantissa(d);

    if (e == 0x7FF)
    {
        return false;
    }

    if (e == 0 && m == 0)
    {
        d = 0; // < relevant part
    }

    value = d;
    return true;
}

如您所见，如果尾数和指数均为零，则将值显式分配给0.因此，您无法更改它.

As you see, if mantissa and exponent are both zero - value is explicitly assigned to 0. So there is no way you can change that.

.NET的完整实现具有NumberBufferToDouble作为InternalCall(在纯C \ C ++中实现)，但是我认为它执行的操作类似.

Full .NET implementation has NumberBufferToDouble as InternalCall (implemented in pure C\C++), but I assume it does something similar.

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