although I flagged this question should be closed as duplicate, keeping it has some additional value because of the multiple different magic number values used, redirecting users encountering different magic values to the same resource.
On modern processors, integer division is one of the slowest arithmetic operations you can have a processor perform. Often orders of magnitude slower than other arithmetic operations.
It turns out that if divisor is constant you can avoid the expensive division operation using clever arithmetic tricks to a set of considerably faster operations (multiplications, additions and shifts), thus reaching overall faster performance at the expense of slightly larger code.
This is often called "division by magic numbers" because those numbers indeed often look like randomly selected numbers, that is not, however, the case. Compilers (and sometimes humans, too) use those tricks often nowadays, since size of code is less of an issue thanks to the exponential growth of storage capacity.
The general approach is that we can develop an equation like the following:
X / Y == X * (1/Y) == sqrt((X * 2^n) * (1/Y)), 2^n) == ((x << n) * 1/Y)>>n
In your case, 0xE38E38E38E38E38Fui64 with a shift of 3 bits is the hardcoded magic number used for division by 9 for unsigned 64 bit integers. Since your code actually shifts by 5, the actual divisor equals 9 * 2^2 = 36.
