Convert UInt32 to float without rounding?

I need to convert a UInt32 type to a float without having it rounded.

That can't be done.

There are 2³² possible uint values. There are fewer than 2³² float values (there are 2³² bit patterns, but that includes various NaN values). Add to that the fact that there are obviously a lot of float values which can't be represented as uint (e.g. 0.5) and it becomes clear that you can't represent every uint value exactly in a float. However, every uint (and every int) can be represented exactly as a double, so that might be a solution to your problem.

The problem you're seeing in your original source code is that 4278190335 isn't exactly representable as a float; the closest float value is 4278190336. This isn't a problem with the conversion from float to uint - it's a problem with the conversion from the exact value you've specified in your source code into a float; the float to uint conversion happens separately (and again, can easily lose information).