[Solved] why < is much faster than !=?

Question

When you call cycle with the input value 113383, the process eventually sets n to
827370449, and 3*827370449+1 is 2482111348, which is greater than the maximum signed int and is interpreted as -1812855948. So there’s your first negative number where there should be no negative number.

If this process then eventually sets n to -2, it will loop infinitely between -2 and -1 from then on. There may be other loops I haven’t considered.

If you were to use an unsigned int, there is a possibility (I haven’t checked) that this too will overflow eventually, which will not result in a negative value but will result in an incorrect value, invalidating your results.

No matter what integer representation you use, it would probably be a good idea to compare n with (maximum-1)/3 at the top of each loop, where maximum is the largest possible positive value of your integer type, just to be sure you do not overflow.

Accepted Answer

When you call cycle with the input value 113383, the process eventually sets n to
827370449, and 3*827370449+1 is 2482111348, which is greater than the maximum signed int and is interpreted as -1812855948. So there’s your first negative number where there should be no negative number.

If this process then eventually sets n to -2, it will loop infinitely between -2 and -1 from then on. There may be other loops I haven’t considered.

If you were to use an unsigned int, there is a possibility (I haven’t checked) that this too will overflow eventually, which will not result in a negative value but will result in an incorrect value, invalidating your results.

No matter what integer representation you use, it would probably be a good idea to compare n with (maximum-1)/3 at the top of each loop, where maximum is the largest possible positive value of your integer type, just to be sure you do not overflow.