64-bit RISC-V (RV64)

Development is underway for Jolt to move from 32-bit RISC-V (RV32IM) 64-bit RISC-V (RV64IMAC).

Benefits

Switching to 64-bit RISC-V should improve prover performance on many guest programs of real-world interest. Many algorithms are designed for 64-bit hardware architectures, e.g. hash functions like Keccak "naturally" operate on 64-bit values. Having larger registers is also conducive for proving big-integer arithmetic, e.g. the EVM natively supports 256-bit arithmetic, and elliptic curves used in cryptography typically have underlying fields of ~256 bits or more.

In addition, some high-level programming languages (notably, Go) support 64-bit RISC-V as a compilation target, but do not support any 32-bit RISC-V targets. By supporting RV64, Jolt will support guest programs written in a broader range of languages.

Performance

We expect the impact on prover time (per-cycle) of switching from RV32IM to RV64IMAC to be well within a factor of two. We hope this will be offsite by the benefits to prover performance of a 64-bit architecture for many guest programs (described above). The impact on proof size and verifier time will be marginal.