What is the best way to evenly scale one byte?

Question

In C I need to scale a uint8_t from 0 - 255 to 0 - 31

What is the best way to do this evenly?

Answer 1

If you're trying to scale from 8 bits to 5 bits, you can do a 3 bit shift;

uint8_t scaled = (uint8_t)(original >> 3);

This drops the lower 3 bits.

Answer 2

You can use some simple multiplication and division:

uint8_t scaled = (uint8_t)(((uint32_t)original * 32U) / 256U);