CODEWITHSUNDEEP
c#integer-division
GazTheDestroyer
GazTheDestroyer

Reputation: 21261

Dividing integer types - Are results predictable?

I have a 64-bit long that I want to round down to the nearest 10,000, so I am doing a simple:

long myLong = 123456789
long rounded = (myLong / 10000) * 10000; //rounded = 123450000

This appears to do what I expect, but as I'm not 100% on the internals of how integer types get divided, I am just slightly concerned that there may be situations where this doesn't work as expected.

Will this still work at very large numbers / edge cases?

Upvotes: 1

Views: 401

Answers (2)

Daniel Daranas
Daniel Daranas

Reputation: 22644

Yes, it will work. The semantics of integer division guarantee what you expect.

However it may be good to write some tests for your specific use case, including edge cases. This will reassure you.

Upvotes: 1

Kieren Johnstone
Kieren Johnstone

Reputation: 42013

Yes, it will work, so long as no result, intermediate or otherwise, exceeds long.MaxValue.

To be explicit about your constants you could use the L specifier at the end, e.g. 123456789L.

For straightforward calculations like this, can I suggest Pex from Microsoft ( http://research.microsoft.com/en-us/projects/pex/ ), which looks for edge cases and tests them. This is a clean-cut example, but if you were building up lots of logic based on things you are unsure of, it's a great tool.

Upvotes: 4

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