C#system.math.pow和SQL-Server Pow函数中的问题 [英] Issue in C# system.math.pow and SQL-Server Pow function

问题描述

HI，

当我们使用system.math.pow函数时，我们面临一个问题.最多2个POW 56，其工作状况良好.我将结果与sql server POW(2.0,56)比较.

从57岁的Pow开始，当与c#和Sql Server结果相适应时，我们在C#和Sql Server中得到了不同的值

示例:

C#
(long)system.math.pow(2,57)

结果-144115188075855872

SQL Server

选择cast(POW(2.0,57)as bigint)

结果-144115188075855870


问候，
Senthil S

We are facing a problem when we use system.math.pow function. Upto 2 POW 56 its working fine. I am comparing the result with sql server POW(2.0,56).

From Pow of 57 onwards,when comaparing c# and Sql Server result we are getting different values in C# and Sql Server

Example:

C#
(long)system.math.pow(2,57)

Result - 144115188075855872

SQL Server

Select cast(POW(2.0,57) as bigint)

Result - 144115188075855870


Regards,
Senthil S

推荐答案

只有当它是整数值时，您才能确定正确的结果.类型System.UInt64足够大，仅因为57< c0; 64，但不是System.UInt32(57> 32).

对2的幂使用Pow函数只是愚蠢的.您需要使用<<向左移动1.运算符，但是对于System.UInt64来说却不是那么容易，因为仅为int定义了该运算符.您可以使用System.BitConverter类非常简单地执行此操作，请参见:
http://msdn.microsoft.com/en-us/library/system.bitconverter.aspx [^ ].

以下是获得确切答案的方法:

You can be sure in a right result only if this is integer value. The type System.UInt64 is big enough, just because 57 < 64, but not System.UInt32 (57 > 32).

Using Pow function for powers of 2 is just silly. You need to shift 1 to the left using << operator, but for System.UInt64 this is not so easy because this operator is only defined for int. You can do it very simply using the class System.BitConverter, please see:
http://msdn.microsoft.com/en-us/library/system.bitconverter.aspx[^].

Here is how to get an exact answer:

static System.UInt64 PowerOfTwo(byte power) {
    byte[] bytes = new byte[sizeof(System.UInt64)];
    int bitShift = power % 8;
    int byteIndex = power / 8;
    bytes[byteIndex] = (byte)(1 << bitShift);
    return System.BitConverter.ToUInt64(bytes, 0);
}

测试中……答案是144115188075855872；您的C#结果正确，SQL Server是骗子！

如果需要更大的值，则唯一的机会就是类型System.Numerics.BigInteger；请参阅:
http://msdn.microsoft.com/en-us/library/system.numerics. biginteger.aspx [ ^ ].

—SA

Testing… the answer is 144115188075855872; your C# result was correct, SQL Server is a liar!

If you need bigger values, your only chance is the type System.Numerics.BigInteger; please see:
http://msdn.microsoft.com/en-us/library/system.numerics.biginteger.aspx[^].

—SA

如果它们不同，则它们也不同.它们在两个地方进行计算.您坐下来确定哪个是正确的吗?

If they are different, then they are different. They are being calculated in two places. Have you sat down to work out which is correct ?

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