Shell Protocol - Shubham's results

Low Risk Issues

Non-Critical Issues

[L-01] Dead Code in _getUtility function

Utility is the pool's internal measure of how much value it holds. The _getUtility function returns the utility based in the input x & y parameters. After performing the necessary calculations, there are checks to ensure the correct value of utility to be returned. But the if condition will never be executed because the value of a & b will never be less than 0. Thus everytime the else statement will be executed.

720:      if(a < 0 && b < 0) utility = (r0 > r1) ? r1 : r0;

[L-02] Confusing code comments deviates from function logic

The mentioned comments above certain checks/functions make it difficult to understand what the code actually wants to implement. For example in most places it says that the "amount cannot be less than 0" but the require statement just below it states the complete opposite.

295:          // amount cannot be less than 0
296:          require(result < 0);


450:          // amount cannot be less than 0
451:          require(result < 0);


459:          @dev We use FEE_UP because we want to increase the perceived amount of     //@note - should be FEE_DOWN
             ..........
481:         FEE_DOWN,


487:          // amount cannot be less than 0
488:          require(result < 0);

[L-03] No check for duration in the constructor

duration is used to set the time for which the curve will evolve. It is used in the Config struct to set the t_final which is used in calculating various parameters. Add a valid check to ensure the duration is not set to the default value.

        constructor(
        int128 py_init,
        int128 px_init,
        int128 py_final,
        int128 px_final,
        uint256 duration
    ) { 
        // price value checks
        if (py_init >= MAX_PRICE_VALUE || py_final >= MAX_PRICE_VALUE) revert MaximumAllowedPriceExceeded();
        if (px_init <= MIN_PRICE_VALUE || px_final <= MIN_PRICE_VALUE) revert MinimumAllowedPriceExceeded();

        // at all times x price should be less than y price
        if (py_init <= px_init) revert InvalidPrice();
        if (py_final <= px_final) revert InvalidPrice();

        // max. price ratio check
        if (py_init.div(py_init.sub(px_init)) > ABDKMath64x64.divu(uint(MAX_PRICE_RATIO), 1)) revert MaximumAllowedPriceRatioExceeded();
        if (py_final.div(py_final.sub(px_final)) > ABDKMath64x64.divu(uint(MAX_PRICE_RATIO), 1)) revert MaximumAllowedPriceRatioExceeded();

        config = LibConfig.newConfig(py_init, px_init, py_final, px_final, duration);
    }

[NC-1] Use of extra parenthesis in the code

Remove extra parenthesis as they serve no purpose & just increase the code size.

515:           {
516:               roundedSpecifiedAmount = _applyFeeByRounding(
517:                   specifiedAmount,
518:                   feeDirection
519:               );
520:           }


525:           {
                ....................
544:           }