Gas Optimizations

[code423n4]

1. Redundant memory slot in LibString library

There is function toString in LibString library. There 5 storage slots are used for the next purposes:

// The maximum value of a uint256 contains 78 digits (1 byte per digit), but we allocate 160 bytes
// to keep the free memory pointer word aligned. We'll need 1 word for the length, 1 word for the
// trailing zeros padding, and 3 other words for a max of 78 digits. In total: 5 * 32 = 160 bytes.

Actually, the last (fifth) storage slot is redundant, it is filled with zero value and never used later:

// Clean the last word of memory it may not be overwritten.
mstore(str, 0)

It is reasonable to not allocate such a slot at all (and to not store there zero value) to reduce gas consumption and make the code more clear.

2. Using preincrement instead of postcrement in loops

There are many places where the index in a loop is incremented by the postincrement i++. The more efficient way to increment the variable is an ++i preincrement. Also, the incrementation of variables can be put in unchecked brackets.

3. Using immutables for all unchangeable storage variables

Although the immutable keyword is used for many of the variables it is not used in all variables where it can be so. As an example, BASE_URI variable from ArtGobblers should be declared with immutable keyword.

[GalloDaSballo]

2k from Immutable

First report should be benchmarked as it's too specific to be accepted at face value