Gas inefficiencies in `KittyMinting`

[Arachnid]

Description

There are a couple of gas inefficiencies in KittyMinting that could be resolved for significantly lower gas consumption:

• promoCreationLimit and gen0CreationLimit are both defined as variables. Making them constant would allow the compiler to optimise them out, saving 40k of deployment-time gas, and ~200 gas each time they are read.
• createPromoKitty increments both variables, costing ~10k. Incrementing only promoCreatedCount, and checking the sum of the two variables instead of each separately, would save ~5k gas at update time.

[dete]

promoCreationLimit and gen0CreationLimit are both defined as variables

Weirdly, I just learned about constant Solidity variables just this morning, I think there some others we can probably fix, also.

createPromoKitty increments both variables

Your suggestion would result in two reads (instead of one) in createGen0Auction, but it's still a net gas savings. We'll definitely look at this!

Thanks again, @Arachnid! Love these reports!

[MacroChip]

@dete As you suspected, here are two more than can be constant https://github.com/axiomzen/cryptokitties-bounty/blob/03b51a8872d2438851d0ef77cfe29c74a079d26a/contracts/KittyOwnership.sol#L13
https://github.com/axiomzen/cryptokitties-bounty/blob/03b51a8872d2438851d0ef77cfe29c74a079d26a/contracts/KittyOwnership.sol#L14

[kimcope]

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