[stableswap]: Convert all core stableswap arithmetic to use BigDec (#…

…2777)

* convert all core stableswap arithmetic to use bigdec

* fix conversion from sdkDec to BigDec

* use correct precision for conversions

* improve readability and update Sdk -> SDK in function names

* fix merge conflicts

osmomath/decimal.go

@@ -498,22 +498,27 @@ func (d BigDec) MustFloat64() float64 {
 
 // SdkDec returns the Sdk.Dec representation of a BigDec.
 // Values in any additional decimal places are truncated.
-func (d BigDec) SdkDec() sdk.Dec {
+func (d BigDec) SDKDec() sdk.Dec {
 	precisionDiff := Precision - sdk.Precision
 	precisionFactor := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(precisionDiff)), nil)
 
 	if precisionDiff < 0 {
 		panic("invalid decimal precision")
 	}
 
-	truncatedDec := sdk.NewDecFromBigIntWithPrec(new(big.Int).Quo(d.BigInt(), precisionFactor), sdk.Precision)
+	// Truncate any additional decimal values that exist due to BigDec's additional precision
+	// This relies on big.Int's Quo function doing floor division
+	intRepresentation := new(big.Int).Quo(d.BigInt(), precisionFactor)
+
+	// convert int representation back to SDK Dec precision
+	truncatedDec := sdk.NewDecFromBigIntWithPrec(intRepresentation, sdk.Precision)
 
 	return truncatedDec
 }
 
 // BigDecFromSdkDec returns the BigDec representation of an SdkDec.
 // Values in any additional decimal places are truncated.
-func BigDecFromSdkDec(d sdk.Dec) BigDec {
+func BigDecFromSDKDec(d sdk.Dec) BigDec {
 	return NewDecFromBigIntWithPrec(d.BigInt(), sdk.Precision)
 }
 

osmomath/decimal_test.go

@@ -167,9 +167,9 @@ func (s *decimalTestSuite) TestSdkDec() {
 	}
 	for tcIndex, tc := range tests {
 		if tc.expPanic {
-			s.Require().Panics(func() { tc.d.SdkDec() })
+			s.Require().Panics(func() { tc.d.SDKDec() })
 		} else {
-			value := tc.d.SdkDec()
+			value := tc.d.SDKDec()
 			s.Require().Equal(tc.want, value, "bad SdkDec(), index: %v", tcIndex)
 		}
 	}
@@ -192,9 +192,9 @@ func (s *decimalTestSuite) TestBigDecFromSdkDec() {
 	}
 	for tcIndex, tc := range tests {
 		if tc.expPanic {
-			s.Require().Panics(func() { BigDecFromSdkDec(tc.d) })
+			s.Require().Panics(func() { BigDecFromSDKDec(tc.d) })
 		} else {
-			value := BigDecFromSdkDec(tc.d)
+			value := BigDecFromSDKDec(tc.d)
 			s.Require().Equal(tc.want, value, "bad BigDecFromSdkDec(), index: %v", tcIndex)
 		}
 	}

x/gamm/pool-models/stableswap/amm.go

@@ -360,9 +360,9 @@ func (p *Pool) calcOutAmtGivenIn(tokenIn sdk.Coin, tokenOutDenom string, swapFee
 	}
 	tokenInSupply, tokenOutSupply := reserves[0], reserves[1]
 	// We are solving for the amount of token out, hence x = tokenOutSupply, y = tokenInSupply
-	cfmmOut := solveCfmm(osmomath.BigDecFromSdkDec(tokenOutSupply), osmomath.BigDecFromSdkDec(tokenInSupply), osmomath.BigDecFromSdkDec(tokenIn.Amount.ToDec()))
+	cfmmOut := solveCfmm(osmomath.BigDecFromSDKDec(tokenOutSupply), osmomath.BigDecFromSDKDec(tokenInSupply), osmomath.BigDecFromSDKDec(tokenIn.Amount.ToDec()))
 	outAmt := p.getDescaledPoolAmt(tokenOutDenom, cfmmOut)
-	return outAmt.SdkDec(), nil
+	return outAmt.SDKDec(), nil
 }
 
 // returns inAmt as a decimal
@@ -374,9 +374,9 @@ func (p *Pool) calcInAmtGivenOut(tokenOut sdk.Coin, tokenInDenom string, swapFee
 	tokenInSupply, tokenOutSupply := reserves[0], reserves[1]
 	// We are solving for the amount of token in, cfmm(x,y) = cfmm(x + x_in, y - y_out)
 	// x = tokenInSupply, y = tokenOutSupply, yIn = -tokenOutAmount
-	cfmmIn := solveCfmm(osmomath.BigDecFromSdkDec(tokenInSupply), osmomath.BigDecFromSdkDec(tokenOutSupply), osmomath.BigDecFromSdkDec(tokenOut.Amount.ToDec().Neg()))
+	cfmmIn := solveCfmm(osmomath.BigDecFromSDKDec(tokenInSupply), osmomath.BigDecFromSDKDec(tokenOutSupply), osmomath.BigDecFromSDKDec(tokenOut.Amount.ToDec().Neg()))
 	inAmt := p.getDescaledPoolAmt(tokenInDenom, cfmmIn.Neg())
-	return inAmt.SdkDec(), nil
+	return inAmt.SDKDec(), nil
 }
 
 func (p *Pool) calcSingleAssetJoinShares(tokenIn sdk.Coin, swapFee sdk.Dec) (sdk.Int, error) {

x/gamm/pool-models/stableswap/pool.go

@@ -243,9 +243,9 @@ func (p Pool) SpotPrice(ctx sdk.Context, baseAssetDenom string, quoteAssetDenom
 		return sdk.Dec{}, err
 	}
 
-	scaledSpotPrice := spotPrice(osmomath.BigDecFromSdkDec(reserves[0]), osmomath.BigDecFromSdkDec(reserves[1]))
+	scaledSpotPrice := spotPrice(osmomath.BigDecFromSDKDec(reserves[0]), osmomath.BigDecFromSDKDec(reserves[1]))
 	spotPrice := p.getDescaledPoolAmt(baseAssetDenom, scaledSpotPrice)
-	spotPriceSdkDec := spotPrice.SdkDec()
+	spotPriceSdkDec := spotPrice.SDKDec()
 
 	return spotPriceSdkDec, nil
 }