Reduce uint256 fields to smaller integer types for gas and storage savings

[pali101]

Description

Currently most fields in structs use uint256 even when their values will never approach 2²⁵⁶ - 1. This wastes storage slots (→ higher SLOAD/SSTORE gas) and bloats contract size.

Proposal

Reduce integer size to smallest size that can hold maximum possible value, then reorder fields so they pack into 32-byte slots wherever possible.

Proposed changes:

• Rail
  • lockupPeriod - uint64 (timestamp / block number)
  • settledUpTo - uint64 (timestamp / block number)
  • endEpoch - uint64 (timestamp / block number)
  • commissionRateBps - uint16 (shares the same range as COMMISSION_MAX_BPS, i.e., 0 to 10,000)
• Account
  • lockupLastSettledAt - uint64 (timestamp / block number)
• PayeeCommissionLimit
  • maxbps - uint16 (0 to 10,000 limit)

Using uint64 for timestamps or block numbers fields enables efficient storage packing, and reduce gas costs. It remains future proof, as 64 bits cover for over 584 billion years of Unix time and block numbers will never approach 2⁶⁴ in any realistic timeframe.

Rationale

Using minimal width integers to tightly pack struct fields can significantly reduce storage gas costs[1].

Next steps

1. Reorder struct fields so contiguous small types pack together.
2. Benchmark gas usage.

[1]: "Tight Variable Packing | Solidity Patterns" https://fravoll.github.io/solidity-patterns/tight_variable_packing.html

[Stebalien]

Yeah, this seems quite reasonable and should save a nice chunk of gas.

[pali101]

Thanks @Stebalien for confirming this approach. I’ve opened PR #85 with the struct-packing optimizations and would appreciate your review.