CODEWITHSUNDEEP
c#
MistyK
MistyK

Reputation: 6232

Modulo vs overflow in int gives different result

I was doing advent of code day15 and as part of it I got an unexpected result. I had to basically calculate 16807 * 16807 * 65 and the value shouldn't be bigger than int.maxValue. I noticed that my result doesn't match with the expected result so when I simplified it, it basically boils down to this(unchecked wasn't used, it's just here to satisfy compiler):

 int a = unchecked(16807 * 16807 * 65); //1181022001
 long b = 16807L * 16807 * 65 % int.MaxValue; //1181022009

There may be something obvious I'm missing.

Upvotes: 0

Views: 84

Answers (1)

Servy
Servy

Reputation: 203825

int.MaxValue + 1, when cast to an integer (in an unchecked context) is int.MinValue (-2,147,483,648). (int.MaxValue + 1L) % int.MaxValue is 1. So yes, they're both different, because they're both defined to do different things.

Upvotes: 2

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