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osmosis-labs · Sep 4, 2023 · 0b8dac1 · 0b8dac1
1 parent 9d4c77e
commit 0b8dac1
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Showing 3 changed files with 64 additions and 5 deletions.
diff --git a/osmomath/decimal.go b/osmomath/decimal.go
@@ -44,6 +44,11 @@ var (
 	oneInt               = big.NewInt(1)
 	tenInt               = big.NewInt(10)
 
+	// precisionFactorSDK is used to adjust the scale of BigDec values to match the precision expected by sdk.Dec
+	precisionFactorSDK *big.Int
+	// precisionDiffFromSDKDec is a difference in precision between BigDec and sdk.Dec
+	precisionDiffFromSDKDec int
+
 	// log_2(e)
 	// From: https://www.wolframalpha.com/input?i=log_2%28e%29+with+37+digits
 	logOfEbase2 = MustNewBigDecFromStr("1.442695040888963407359924681001892137")
@@ -69,6 +74,13 @@ func init() {
 	for i := 0; i <= PrecisionBigDec; i++ {
 		precisionMultipliers[i] = calcPrecisionMultiplier(int64(i))
 	}
+
+	precisionDiffFromSDKDec = PrecisionBigDec - sdk.Precision
+	if precisionDiffFromSDKDec < 0 {
+		panic("invalid decimal precision")
+	}
+
+	precisionFactorSDK = new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(precisionDiffFromSDKDec)), nil)
 }
 
 func precisionInt() *big.Int {
@@ -552,19 +564,25 @@ func (d BigDec) MustFloat64() float64 {
 // Dec returns the osmomath.Dec representation of a BigDec.
 // Values in any additional decimal places are truncated.
 func (d BigDec) Dec() Dec {
-	precisionDiff := PrecisionBigDec - PrecisionDec
-	precisionFactor := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(precisionDiff)), nil)
+	return d.DecWithPrecision(sdk.Precision)
+}
 
-	if precisionDiff < 0 {
-		panic("invalid decimal precision")
+func (d BigDec) DecWithPrecision(precision int64) Dec {
+	var precisionFactor *big.Int
+	if precision >= sdk.Precision {
+		precisionFactor = precisionFactorSDK
+		precision = sdk.Precision
+	} else {
+		precisionDiff := PrecisionBigDec - precision
+		precisionFactor = new(big.Int).Exp(big.NewInt(10), big.NewInt(precisionDiff), nil)
 	}
 
 	// 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 := NewDecFromBigIntWithPrec(intRepresentation, PrecisionDec)
+	truncatedDec := NewDecFromBigIntWithPrec(intRepresentation, precision)
 
 	return truncatedDec
 }

diff --git a/osmomath/decimal_test.go b/osmomath/decimal_test.go
@@ -7,6 +7,7 @@ import (
 	"math/big"
 	"testing"
 
+	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
 	"gopkg.in/yaml.v2"
@@ -1480,3 +1481,42 @@ func (s *decimalTestSuite) TestPower() {
 		})
 	}
 }
+
+func (s *decimalTestSuite) TestDecWithPrecision() {
+	tests := []struct {
+		d         osmomath.BigDec
+		want      osmomath.Dec
+		precision int64
+		expPanic  bool
+	}{
+		// test cases for basic SDKDec() conversion
+		{osmomath.NewBigDec(0), sdk.MustNewDecFromStr("0.000000000000000000"), sdk.Precision, false},
+		{osmomath.NewBigDec(1), sdk.MustNewDecFromStr("1.000000000000000000"), sdk.Precision, false},
+		{osmomath.NewBigDec(10), sdk.MustNewDecFromStr("10.000000000000000000"), sdk.Precision, false},
+		{osmomath.NewBigDec(12340), sdk.MustNewDecFromStr("12340.000000000000000000"), sdk.Precision, false},
+		{osmomath.NewBigDecWithPrec(12340, 4), sdk.MustNewDecFromStr("1.234000000000000000"), sdk.Precision, false},
+		{osmomath.NewBigDecWithPrec(12340, 5), sdk.MustNewDecFromStr("0.123400000000000000"), sdk.Precision, false},
+		{osmomath.NewBigDecWithPrec(12340, 8), sdk.MustNewDecFromStr("0.000123400000000000"), sdk.Precision, false},
+		{osmomath.NewBigDecWithPrec(1009009009009009009, 17), sdk.MustNewDecFromStr("10.090090090090090090"), sdk.Precision, false},
+		// test cases w/ custom precision:
+		{osmomath.NewBigDec(0), sdk.MustNewDecFromStr("0.000000000000"), 12, false},
+		{osmomath.NewBigDec(1), sdk.MustNewDecFromStr("1.000000000000"), 12, false},
+		// specified precision is the same as the initial precision: 12.3453123123 -> 12.3453123123
+		{osmomath.NewBigDecWithPrec(123453123123, 10), sdk.MustNewDecFromStr("12.3453123123"), 10, false},
+		// cut precision to 5 decimals: 3212.4623423462346 - 3212.46234
+		{osmomath.NewBigDecWithPrec(32124623423462346, 13), sdk.MustNewDecFromStr("3212.46234"), 5, false},
+		// no decimal point: 18012004 -> 18012004
+		{osmomath.NewBigDecWithPrec(18012004, 0), sdk.MustNewDecFromStr("18012004"), 13, false},
+		// if we try to convert to sdk.Dec while specifying bigger precision than sdk.Dec has, converts with maximum precision possible (sdk.Precision)
+		{osmomath.NewBigDecWithPrec(1009009009009009009, 17), sdk.MustNewDecFromStr("10.090090090090090090"), sdk.Precision + 2, false},
+	}
+
+	for tcIndex, tc := range tests {
+		if tc.expPanic {
+			s.Require().Panics(func() { tc.d.DecWithPrecision(tc.precision) })
+		} else {
+			value := tc.d.DecWithPrecision(tc.precision)
+			s.Require().Equal(tc.want, value, "bad SdkDec(), index: %v", tcIndex)
+		}
+	}
+}
diff --git a/osmomath/go.sum b/osmomath/go.sum
@@ -302,6 +302,7 @@ github.com/onsi/ginkgo v1.16.4/go.mod h1:dX+/inL/fNMqNlz0e9LfyB9TswhZpCVdJM/Z6Vv
 github.com/onsi/gomega v1.7.1/go.mod h1:XdKZgCCFLUoM/7CFJVPcG8C1xQ1AJ0vpAezJrB7JYyY=
 github.com/onsi/gomega v1.10.1/go.mod h1:iN09h71vgCQne3DLsj+A5owkum+a2tYe+TOCB1ybHNo=
 github.com/onsi/gomega v1.27.10 h1:naR28SdDFlqrG6kScpT8VWpu1xWY5nJRCF3XaYyBjhI=
+github.com/onsi/gomega v1.27.10/go.mod h1:RsS8tutOdbdgzbPtzzATp12yT7kM5I5aElG3evPbQ0M=
 github.com/osmosis-labs/cosmos-sdk v0.45.0-rc1.0.20230829222007-529c69c19915 h1:1VDV+B0rHSrbHjZz7P1tEjZTb2nro/GAhbOT8RAoQcw=
 github.com/osmosis-labs/cosmos-sdk v0.45.0-rc1.0.20230829222007-529c69c19915/go.mod h1:L6USUt+QX9lIqUVCRs8DFEVRZJbCYbemmtcXb7GfHYE=
 github.com/pascaldekloe/goe v0.1.0 h1:cBOtyMzM9HTpWjXfbbunk26uA6nG3a8n06Wieeh0MwY=