In the roundAheadWithPrice function, if zeroForOne and the roundedTick is negative, the tickSpacing is subtracted from the rounded tick. Otherwise if !zeroForOne and the roundedTick is positive, the tickSpacing is added to the rounded tick.

Therefore for the zeroForOne case a positive roundedTick is rounded down and not adjusted upwards, meanwhile a negative roundedTick is adjusted to be more negative. Both of these are rounding back rather than rounding ahead for a zeroForOne position.

For the !zeroForOne case a positive roundedTick is adjusted upwards, meanwhile a negative roundedTick is rounded to be less negative and is not adjusted to be more negative. Both of these are rounding back rather than rounding ahead for a !zeroForOne position.

Ultimately this results in the beginning of a position being resized to the roundedBack tick rather than the roundedAhead tick which unexpectedly alters the user’s overall execution price and unexpectedly sets the latest swapEpoch on the roundedBack tick.

Additionally, the roundAhead function implements incorrect tick rounding where for zeroForOne cases where the roundedTick is negative it is rounded up twice. First the magnitude of the negative tick is reduced with rounding and then it is further adjusted up by the tickSpacing. On the other hand, positive roundedTicks are rounded down and not adjusted up. The inverses are true for the !zeroForOne case.

In the picture above it is clear that tick 5 is incorrectly rounded to tick 0 when it should be rounded to tick 10 and tick -15 is rounded up twice to tick 0 when it should be rounded to tick -10.

In addition to the issues mentioned above, the roundBack, roundBackWithPrice, roundAhead and roundAheadWithPrice functions do not behave appropriately when the roundedTick is 0. If the roundedTick is 0, the original tick may have been either positive or negative and the roundedTick needs to be adjusted by a tickSpacing accordingly.

Recommendation

Use the following cases to accurately round ahead:

if (zeroForOne && (roundedTick > 0 || (roundedTick == 0 && tick > 0))) roundedTick += tickSpacing;
else if (!zeroForOne && (roundedTick < 0 || (roundedTick == 0 && tick < 0))) roundedTick -= tickSpacing;

And use the following cases to accurately round back:

if (zeroForOne && (roundedTick < 0 || (roundedTick == 0 && tick < 0))) roundedTick -= tickSpacing;
else if (!zeroForOne && (roundedTick > 0 || (roundedTick == 0 && tick > 0))) roundedTick += tickSpacing;