A single 1 byte could be from 0 to 255. I intend to rescale it to be from 0 to 7. I have done this:

bit8 := uint8(136)

// To re-scale 1 byte from 0 to 2^3-1 i.e. 0 to 7
bit3 := bit8 / 0xff * 0b0111

The resulting bit3 is 0, but I expect it to be 3 or 4 depending upon rounding down or up. Since the floating point exact value would be 136/255*7 = 3.733333333.

How can I achieve my desired output? Rounding up and down doesn't matter at this point. Whatever is convenient is fine.

Note

I want the operation to be as efficient as possible. Because it's going to be done inside a loop. So, the solutions like below are not optimal:

bit8 := uint8(136)

// To re-scale 1 byte from 0 to 2^3-1 i.e. 0 to 7
bit3 := uint8(float64(bit8) / 255.0 * 7.0)

Take the top 3 bits of the byte (this rounds down):

bit3 := bit8 >> 5