This is an unsigned int, so the expectation would be to do integer division, which would not get you the same result as multiplying by the inverse.
> On Skylake [...] 32/64-bit floating point multiplication has a 4 cycle latency with a throughput of 2 instructions / cycle.
Of course, there are some operations that are very expensive (trigonometric functions, for example), but they're not necessary here, and they're also very expensive on the GPU.