SHL : logic SHift Left (multiply by a power of two)

The bits of the source register (snd) are shifted towards the MSB, by a number of bits indicated either by

• a 4-bit immediate value (short immediate or extended immediate forms)
• the other register (si4) (short register or extended register forms)
• a 16-bit value (long immediate form).

The LSB of the result are filled with 0s.