u256

A 256-bit unsigned integer in four 64-bit limbs, for EVM amounts, with checked arithmetic and hex parsing.

Rust has u128, which is not enough: a single wei balance in a realistic contract exceeds it, and every ABI word is 256 bits. Pulling in a bignum crate is usually the right answer in production, but it is a large dependency for a tool that only needs add, subtract, multiply and divide by small integers.

What is here

• from_hex / to_hex / to_decimal, tolerant of 0x, mixed case and leading zeros, rejecting anything over 32 bytes.
• checked_add, checked_sub, checked_mul_u64, checked_div_u64. All return Option, never wrap. Silent overflow on a balance is the bug that costs money.
• Big-endian byte conversion, which is the layout ABI encoding uses.

What is deliberately missing

• No general multiplication or division. Only by a u64. Full 256x256 multiplication is a different amount of code and not needed to display or compare amounts.
• No signed arithmetic. EVM's SDIV/SMOD are rarely needed off-chain.
• No modular exponentiation. Use a dedicated crate for anything cryptographic.

Development

cargo test

License

MIT