Assuming the basic shape of the expression is correct (so, you want to express the change as a percentage of UInt32.MaxValue, not as a percentage of the old or new value), the problem is that multiplying the difference by 100 overflows. It could be fixed by temporarily using an ulong like this:
uint OriginInt=32654, NewInt=4256321445;
(uint)(((ulong)NewInt - OriginInt) * 100 / uint.MaxValue);
The result is 99.
Of course since this is still integer arithmetic, it will still be the case that the result is rounded down, so a small percentages (below 1) would still result in zero.
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