[gsg]

That's one possible design, but it's common to use a constant pool. Placing constants in the instruction stream is possible but awkward, since there is no guarantee that they are either aligned or of the right endianness (assuming you are trying to write a more or less portable system).

Constants that fit in a byte don't have this problem and can be easily placed in the instruction stream using dedicated byte constant instructions, sometimes including dedicated single-byte instructions for common constants like zero, one, etc.