Comparisons and overflow/underflow on `Felt`
- 主要言語
- TypeScript
- スター
- 10
- フォーク
- 50
- 平均マージ
- 22日 23時間
- マージ済み PR(30日)
- 1
説明
## Felt Comparison
https://docs.miden.xyz/builder/tutorials/rust-compiler/miden-bank/constants-constraints#safe-felt-comparisons says:
> Never use `<`, `>`, `<=`, or `>=` operators directly on `Felt` values. They produce incorrect results due to field element ordering.
Is this still accurate? It looks like `miden_field::Felt` properly uses the built-in instructions for this which shouldn't produce "incorrect" results (I'm not sure what exactly we mean by that).
## Safe Arithmetic
Similarly, the miden bank tutorial has a large section on the dangers of underflows: https://docs.miden.xyz/builder/tutorials/rust-compiler/miden-bank/asset-management#step-2-add-the-withdraw-method-skeleton.
Ideally this would be easy for users to avoid, e.g. by implementing `checked*` arithmetic for the `miden_field::Felt` type , so users can easily do things like `current_balance.checked_sub(withdraw_amount).expect("insufficient balance")`.
If correct/agreed, we'd have to open an issue in `miden-crypto`.
An even safer alternative, at least for on-chain users, would be to let `impl Add for Felt` (and all such related impls) panic instead of wrap around. We'd implement `wrapping_add` and such instead for explicit use. In other words, it'd be ideal to follow the safe design of arithmetic functionality on the Rust primitive types and have `Felt::{wrapping_add, checked_add, overflowing_add, ...}`.
Maybe we could selectively do this only for the `miden_field::Felt` type in `wasm32`, which would be ideal to not have to touch the non-wasm parts, though even that might be doable.
cc @greenhat for thoughts
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