available effective value calc

[nialexsan]

align changes with DeFi Actions Math Utilis to UInt128 and 10^24 decimal places
tweaked variance to address rounding errors in tests

[codecov]

Codecov Report

❌ Patch coverage is 67.56757% with 36 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cadence/contracts/TidalProtocol.cdc	67.56%	36 Missing ⚠️

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[sisyphusSmiling]

Nice work @nialexsan! The utils are much less verbose and rounding operations look good.

[sisyphusSmiling]

Curious why we no longer have to concern ourselves with these conditions

[nialexsan]

for this comment

$$\begin{aligned} C = effectiveCollateralAfterDeposit \\\ D = effectiveDebtAfterDeposit \\\ H = healthAfterDeposit \\\ T = targetHealth \\\ \\\ H = C / D \\\ \\\ availableHealth = H - T \\\ \end{aligned}$$

availableHealth could be UInt128.max only when effectiveDebtAfterDeposit($$D$$) is 0, which should set
$$availableEffectiveValue = C - T * D = C - T * 0 = C$$

and the second branch is the same as the one-liner:

$$\begin{aligned} availableHealth * D = \\ = (H - T) * D = \\\ = H * D - T * D = \\\ = {C * \cancel{D} \over \cancel{D}} - T * D = \\\ = C - T*D \end{aligned}$$

[sisyphusSmiling]

Is there a reason we can't implement this directly? Something like

let base = DeFiActionsMathUtils.mul(oldIndex, perSecondRate)
// would require pow to take UInt128 exponent value
return DeFiActionsMathUtils.pow(base, to: DeFiActionsMathUtils.toUInt128(elapsedSeconds))

Maybe because the bitwise operations are more performant, but we should explicitly state that in a comment since the implementation is not as intuitive as the direct implementation.

[nialexsan]

I'll need to look into it again