⚡️ Optimize SignedWadMath edge case check

[Philogy]

Description

I've changed the SignedWadMul.wadMul to do the overflow & edge case check in one if:

if iszero(
    and(
        or(iszero(x), eq(sdiv(r, x), y)),
        or(lt(x, not(0)), sgt(y, 0x8000000000000000000000000000000000000000000000000000000000000000))
    )
) {
    revert(0, 0)
}

This saves gas at runtime for all cases except the edge case because the resulting bytecode only uses 1 JUMPI vs. 2 to check the conditions. Branches are currently quite expensive making it worth the slightly higher cost of combining multiple expressions.

To save further gas I've transformed the !(x == -1 && y == type(int256).min) check into x != -1 || y != type(int256).min to minimize the use of ISZERO. The inequality checks both need to have binary results so the resulting bitwise expression and(no_overflow, or(x_not_neg1, y_not_min_signed)) equates the logical expression across the whole set of values. To achieve this LT and SGT are abused as != operators, this is possible here as -1 represents the highest possible unsigned integer and 0x8000000000000000000000000000000000000000000000000000000000000000 the lowest signed number.

The final inline-assembly expression represents:

require(
    (x == 0 || (r / x == y))
    && (x != -1 || y != type(int256).min)
);

Checklist

• Ran forge snapshot?
• Ran npm run lint?
• Ran forge test?

Pull requests with an incomplete checklist will be thrown out.

[transmissions11]

nice, lgtm!