.NET与Mono：从2 ^ 32转换为int的不同结果

Question

TL;DR Why does the (int)Math.Pow(2,32) return 0 on Mono and Int32.MinValue on .NET ?

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While testing my .NET-written code on Mono I've stumbled upon the following line:

var i = X / ( (int)Math.Pow(2,32) ); well that line doesn't make much sense of course and I've already changed it to long .

I was however curious why didn't my code throw DivideByZeroException on .NET so I've checked the return value of that expression on both Mono and .NET

Can anyone please explain me the results?

Answer 1

IMHO the question is academic; the documentation promises only that "the result is an unspecified value of the destination type" , so each platform is free to do whatever it wants.

One should be very careful when casting results that might overflow. If there is a possibility of that, and it's important to get a specific result instead of whatever arbitrary implementation a given platform has provided, one should use the checked keyword and catch any OverflowException that might occur, handling it with whatever explicit behavior is desired.

Answer 2

"the result is an unspecified value of the destination type". I thought it would be interesting to see what's actually happening in the .NET implementation.

It's to do with the OpCodes.Conv_I4 Field in IL: " Conversion from floating-point numbers to integer values truncates the number toward zero. When converting from a float64 to a float32, precision can be lost. If value is too large to fit in a float32 (F), positive infinity (if value is positive) or negative infinity (if value is negative) is returned. If overflow occurs converting one integer type to another, the high order bits are truncated" It does once again say overflow is unspecified however.