Excluding the compact instruction set, the standard instructions in RISC-V are all 32 bits. Regardless, RISC-V leaves open the possibility of longer instructions. This is encoded with specific bits in instructions [1].

If \(x\) is the binary encoding of an instruction in RISC-V, then if

\(x \land 11_2 \neq 11_2\), then it is 16 bits.

\(x \land 11_2 = 11_2\) and \(x \land 11100_2 \neq 11100_2\), then it is 32 bits.

\(x \land 111111_2 = 011111_2\), then it is 48 bits.

\(x \land 1111111_2 = 0111111_2\), then it is 64 bits.

\(x \land 1111111_2 = 1111111_2\), \(x \land (111_2 \times 2^{12}) = n\), and \(n \neq 111_2\), then it is \((80+16n)\) bits.

\(x \land 1111111_2 = 1111111_2\) and \(x \land (111_2 \times 2^{12}) = 111_2 \times 2^{12}\), then it will be 192 bits or longer.

The specifics of encoding the length of instructions that are longer than 192 bits have yet to be specified.

## See also

## References

*The RISC-V instruction set manual, volume I: User-level ISA, document version 20191213*. RISC-V Foundation. Document Version 20191213