miden-field

A unified field element type for Miden Rust code that needs to run in two very different environments:

• Off-chain (native, or regular Wasm): Felt is a thin wrapper around Plonky3’s Goldilocks field element.
• On-chain (Wasm compiled for the Miden VM): Felt is represented using Miden compiler intrinsics.

Motivation

In the Miden on-chain execution environment, field elements are currently represented by the compiler using a Wasm primitive type (f32) that the compiler “reinterprets” as a felt. That works for on-chain code generation, but it means the on-chain Felt is not the same type as the off-chain Felt used throughout the Rust ecosystem.

The result is that any code meant to be shared between on-chain and off-chain ends up either:

• duplicated, or
• littered with #[cfg(...)] gates and wrapper types to bridge the two representations.

miden-field exists to provide a single miden_field::Felt API surface that compiles in both contexts without forcing downstream crates to pick a side.

How it works

miden-field uses conditional compilation to select the backing implementation:

• cfg(all(target_family = "wasm", miden)) (on-chain): Felt is a #[repr(transparent)] record with an inner: f32 field (matching the WIT shape expected by bindings). Arithmetic and conversions are implemented by calling Miden compiler intrinsics (e.g. intrinsics::felt::add), and f32 is never treated as a floating-point number.
• otherwise (off-chain): Felt is #[repr(transparent)] over p3_goldilocks::Goldilocks and implements the usual field traits. The modulus is the Goldilocks prime 2^64 - 2^32 + 1.

The rest of the crate (e.g. Word) builds on top of Felt and therefore works in both environments as well.