2 ms·
> you could burn the top 2b to mark instructions as 2/4/6/8 bytes (or whatever) in length. FWIW, this is exactly what RISC-V does.
by atq2119 6y ago
> you could burn the top 2b to mark instructions as 2/4/6/8 bytes (or whatever) in length.
FWIW, this is exactly what RISC-V does.
- TwoBit 6y agoHow is this so? I thought RISC-V was fixed length, except for 16 bit compressed instructions. And afaik those aren't identified by a singular particular bit.
- atq2119 6y agoSee section 1.5 ("Base Instruction-Length Encoding") of the RISC-V spec. It's actually a bit more complex than just using 2 bits (I had forgotten those details), but the basic idea is the same in that there is a fixed cascade of bits identifying the instruction length. There aren't any standard extensions with instructions >32b yet, but the extensibility is there in the base spec.