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负到-1,0到0,正到1

.net

serhio · 技术社区 · 15 年前

MyEnum (Neg -1; None 0; Pos 1)

CompareTo() 初始化该枚举的对象。

性能最好的 如何在.NET中执行(负到-1,0到0,正到1)?

注意。

9 回复 | 直到 13 年前

Henrik 15 年前

看一看 Math.Sign

knittl 15 年前

Math.Sign 在.net框架中

stevehipwell 15 年前

Math.Sign . 但是,如果您对.Net框架在幕后做什么感兴趣,下面的代码已经从Reflector中出来了。

public static int Sign(int value)
{
  if (value < 0)
  {
    return -1;
  }
  if (value > 0)
  {
    return 1;
  }
  return 0;
}

mbeckish 15 年前

Math.Sign(value)

GvS 15 年前

比较结果为负、零或正。如果你看其他答案,Math.Sign使用2个If语句返回int。

(如果这不是家庭作业,我会给出一个代码示例,但你应该从中学习)。

在那之后,测试它,看看什么是最有效的。

serhio 15 年前

测试结果(双核,x86):

''''''''''''''''''''' DEBUG MODE '''
= 1 =
Division took    00:00:06.2482408 ms
BuiltInSign took 00:00:05.0293383 ms <<<
BitTestSign took 00:00:05.2092181 ms
CustomSign took  00:00:05.2512802 ms

= 2 =
Division took    00:00:06.2477787 ms
BuiltInSign took 00:00:05.0330921 ms <<<
BitTestSign took 00:00:05.2114098 ms
CustomSign took  00:00:05.2556966 ms

= 3 =
Division took    00:00:06.2506690 ms
BuiltInSign took 00:00:05.0388615 ms <<<
BitTestSign took 00:00:05.2306954 ms
CustomSign took  00:00:05.2512391 ms


''''''''''''''''''' RELEASE MODE '''
= 1 =
Division took    00:00:01.0974078 ms
BuiltInSign took 00:00:00.3195232 ms
BitTestSign took 00:00:00.6392142 ms
CustomSign took  00:00:00.3194230 ms <<<

= 2 =
Division took    00:00:01.1007138 ms
BuiltInSign took 00:00:00.3197784 ms <<<
BitTestSign took 00:00:00.6395294 ms
CustomSign took  00:00:00.3202774 ms

= 3 =
Division took    00:00:01.0977087 ms
BuiltInSign took 00:00:00.3194622 ms <<<
BitTestSign took 00:00:00.6394220 ms
CustomSign took  00:00:00.3201607 ms

代码:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        Stopwatch sw = new Stopwatch();
        MyEnum myEnum = MyEnum.None;

        const int max = 100000000;

        sw.Start();
        for (int i = -max; i < max; i++)
        {
            myEnum = Division(i);
        }
        sw.Stop();
        Console.WriteLine("Division took {0} ms", sw.Elapsed);
        sw.Reset();

        sw.Start();
        for (int i = -max; i < max; i++)
        {
            myEnum = BuiltInSign(i);
        }
        sw.Stop();
        Console.WriteLine("BuiltInSign took {0} ms", sw.Elapsed);
        sw.Reset();

        sw.Start();
        for (int i = -max; i < max; i++)
        {
            myEnum = BitTestSign(i);
        }
        sw.Stop();
        Console.WriteLine("BitTestSign took {0} ms", sw.Elapsed);
        sw.Reset();

        sw.Start();
        for (int i = -max; i < max; i++)
        {
            myEnum = CustomSign(i);
        }
        sw.Stop();
        Console.WriteLine("CustomSign took {0} ms", sw.Elapsed);
    }

    private MyEnum Division(int value)
    {
        return value == 0 ? 0 : (MyEnum)(value / Math.Abs(value));
    }

    private MyEnum BuiltInSign(int value)
    {
        return (MyEnum)Math.Sign(value);
    }

    private MyEnum CustomSign(int value)
    {
        if (value < 0)
            return MyEnum.Neg;

        if (value > 0)
            return MyEnum.Pos;

        return MyEnum.None;
    }

    MyEnum BitTestSign(int value)
    {
        // Shifts the variable over 31 places, 
        // if the MSB is 1, the statement is true
        if ((value >> 31) == 1)
        {
            return MyEnum.Neg;
        }
        else
        {
            if (value == 0)
            {
                return MyEnum.None;
            }
            else
            {
                return MyEnum.Pos;
            }
        }
    }

    private enum MyEnum
    {
        Pos = 1,
        None = 0,
        Neg = -1
    }
}

Donnie 15 年前

伪代码:

if(num == 0)
  return 0;

if(num has msb set)
  return -1;

return 1;

Turing Complete 15 年前

如果我理解正确的话,您希望返回-1表示负值,0表示零值,1表示正值。

我同意:

public static MyEnum GetSign(int value)
{
    return value == 0 ? 0 : (MyEnum)(value / Math.Abs(value));
}

还是我做错什么了?

Jan Gorzny 15 年前

int Sign(int value){
    if (value >> 31) { //Shifts the variable over 31 places, if the MSB is 1, the statement is true
         return -1;
    } else {
        if (value == 0){
            return 0;
        } else {
            return 1;
        }
    }  }

(例如编辑)