refactor(osmomath): limit pow iterations in osmomath

CHANGELOG.md

@@ -55,7 +55,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * [#6309](https://github.com/osmosis-labs/osmosis/pull/6309) Add  Cosmwasm Pool Queries to Stargate Query
 * [#6493](https://github.com/osmosis-labs/osmosis/pull/6493) Add PoolManager Params query to Stargate Whitelist
 * [#6421](https://github.com/osmosis-labs/osmosis/pull/6421) Moves ValidatePermissionlessPoolCreationEnabled out of poolmanager module
-
+* [#6627](https://github.com/osmosis-labs/osmosis/pull/6627) Limit pow iterations in osmomath.
 
 ## v19.2.0
 

go.mod

@@ -22,7 +22,7 @@ require (
 	github.com/mattn/go-sqlite3 v1.14.17
 	github.com/ory/dockertest/v3 v3.10.0
 	github.com/osmosis-labs/go-mutesting v0.0.0-20221208041716-b43bcd97b3b3
-	github.com/osmosis-labs/osmosis/osmomath v0.0.7-0.20230924192433-36cf2950dca4
+	github.com/osmosis-labs/osmosis/osmomath v0.0.7-0.20231003135651-7418f98f1a04
 	github.com/osmosis-labs/osmosis/osmoutils v0.0.7-0.20230929193736-aae32321cac7
 	github.com/osmosis-labs/osmosis/x/epochs v0.0.3-0.20230911120014-b14342e08daf
 	github.com/osmosis-labs/osmosis/x/ibc-hooks v0.0.9-0.20230911120014-b14342e08daf

go.sum

@@ -966,6 +966,8 @@ github.com/osmosis-labs/go-mutesting v0.0.0-20221208041716-b43bcd97b3b3 h1:Ylmch
 github.com/osmosis-labs/go-mutesting v0.0.0-20221208041716-b43bcd97b3b3/go.mod h1:lV6KnqXYD/ayTe7310MHtM3I2q8Z6bBfMAi+bhwPYtI=
 github.com/osmosis-labs/osmosis/osmomath v0.0.7-0.20230924192433-36cf2950dca4 h1:venI3u6DjxKcQbjiCO3V8s0ww/jx+cAZRkpwLHadms8=
 github.com/osmosis-labs/osmosis/osmomath v0.0.7-0.20230924192433-36cf2950dca4/go.mod h1:IlCTpM2uoi8SUAigc9r9kAaoz7K5H9O84u7CwaTLDdY=
+github.com/osmosis-labs/osmosis/osmomath v0.0.7-0.20231003135651-7418f98f1a04 h1:C8LtPGkhJxfJNj7Xtok1If5yAV53O6XG3USaOJSgeg4=
+github.com/osmosis-labs/osmosis/osmomath v0.0.7-0.20231003135651-7418f98f1a04/go.mod h1:jtOM+8RJMOn5e8YIaodzvO0b8kvBcHDgtCVCmWrx6wU=
 github.com/osmosis-labs/osmosis/osmoutils v0.0.7-0.20230929193736-aae32321cac7 h1:E5rwhxKEt6XOIfLkoLNiqCCFNCymJjiwMYIP+0ABMKM=
 github.com/osmosis-labs/osmosis/osmoutils v0.0.7-0.20230929193736-aae32321cac7/go.mod h1:YT53hlXr54D4MVKp3eoBxigiiYvy3F+h+xTZuGPW5R8=
 github.com/osmosis-labs/osmosis/x/epochs v0.0.3-0.20230911120014-b14342e08daf h1:8lkIsAj3L7zxvOZbqVLNJRpSdDxaYhYfAIG7XjPaJiU=

osmomath/math.go

@@ -8,6 +8,8 @@ import (
 // TODO: Analyze choice here.
 var powPrecision, _ = NewDecFromStr("0.00000001")
 
+const powIterationLimit = 245_000
+
 var (
 	one_half Dec = MustNewDecFromStr("0.5")
 	one      Dec = OneDec()
@@ -81,8 +83,8 @@ func Pow(base Dec, exp Dec) Dec {
 
 // Contract: 0 < base <= 2
 // 0 <= exp < 1.
-func PowApprox(base Dec, exp Dec, precision Dec) Dec {
-	if !base.IsPositive() {
+func PowApprox(originalBase Dec, exp Dec, precision Dec) Dec {
+	if !originalBase.IsPositive() {
 		panic(fmt.Errorf("base must be greater than 0"))
 	}
 
@@ -93,7 +95,7 @@ func PowApprox(base Dec, exp Dec, precision Dec) Dec {
 	// Common case optimization
 	// Optimize for it being equal to one-half
 	if exp.Equal(one_half) {
-		output, err := base.ApproxSqrt()
+		output, err := originalBase.ApproxSqrt()
 		if err != nil {
 			panic(err)
 		}
@@ -129,7 +131,7 @@ func PowApprox(base Dec, exp Dec, precision Dec) Dec {
 	// TODO: Check with our parameterization
 	// TODO: If theres a bug, balancer is also wrong here :thonk:
 
-	base = base.Clone()
+	base := originalBase.Clone()
 	x, xneg := AbsDifferenceWithSign(base, one)
 	term := OneDec()
 	sum := OneDec()
@@ -166,6 +168,10 @@ func PowApprox(base Dec, exp Dec, precision Dec) Dec {
 		} else {
 			sum.AddMut(term)
 		}
+
+		if i == powIterationLimit {
+			panic(fmt.Errorf("failed to reach precision within %d iterations, best guess: %s for %s^%s", powIterationLimit, sum, originalBase, exp))
+		}
 	}
 	return sum
 }

osmomath/math_test.go

@@ -23,6 +23,7 @@ func TestAbsDifferenceWithSign(t *testing.T) {
 
 func TestPowApprox(t *testing.T) {
 	testCases := []struct {
+		expectPanic    bool
 		base           Dec
 		exp            Dec
 		powPrecision   Dec
@@ -44,10 +45,10 @@ func TestPowApprox(t *testing.T) {
 		},
 		{
 			// zero base, this should panic
-			base:           ZeroDec(),
-			exp:            OneDec(),
-			powPrecision:   MustNewDecFromStr("0.00001"),
-			expectedResult: ZeroDec(),
+			base:         ZeroDec(),
+			exp:          OneDec(),
+			powPrecision: MustNewDecFromStr("0.00001"),
+			expectPanic:  true,
 		},
 		{
 			// large base, small exp
@@ -84,17 +85,46 @@ func TestPowApprox(t *testing.T) {
 			powPrecision:   MustNewDecFromStr("0.00000001"),
 			expectedResult: OneDec(),
 		},
+		{
+			// base close to 2
+
+			base:         MustNewDecFromStr("1.999999999999999999"),
+			exp:          SmallestDec(),
+			powPrecision: powPrecision,
+			// In Python: 1.000000000000000000693147181
+			expectedResult: OneDec(),
+		},
+		{
+			// base close to 2 and hitting iteration bound
+
+			base:         MustNewDecFromStr("1.999999999999999999"),
+			exp:          MustNewDecFromStr("0.1"),
+			powPrecision: powPrecision,
+
+			// In Python: 1.071773462536293164
+
+			expectPanic: true,
+		},
+		{
+			// base close to 2 under iteration limit
+
+			base:         MustNewDecFromStr("1.99999"),
+			exp:          MustNewDecFromStr("0.1"),
+			powPrecision: powPrecision,
+			// In Python: 1.071772926648356147102864087
+			expectedResult: MustNewDecFromStr("1.071772926648356147"),
+		},
 	}
 
 	for i, tc := range testCases {
 		var actualResult Dec
-		ConditionalPanic(t, tc.base.IsZero(), func() {
+		ConditionalPanic(t, tc.expectPanic, func() {
 			fmt.Println(tc.base)
 			actualResult = PowApprox(tc.base, tc.exp, tc.powPrecision)
 			require.True(
 				t,
 				tc.expectedResult.Sub(actualResult).Abs().LTE(tc.powPrecision),
-				fmt.Sprintf("test %d failed: expected value & actual value's difference should be less than precision", i),
+				fmt.Sprintf("test %d failed: expected value & actual value's difference should be less than precision, expected: %s, actual: %s, precision: %s", i, tc.expectedResult, actualResult, tc.powPrecision),
 			)
 		})
 	}

osmomath/pow_bench_test.go

@@ -89,7 +89,13 @@ func BenchmarkSlowPowCases(b *testing.B) {
 		exp  Dec
 	}{
 		{
-			base: MustNewDecFromStr("1.99999999999999"),
+			// Original worst case:
+			// 1.99999999999999
+			// 0.1
+			//
+			// The values below are hand-picked to be close to the worst case
+			// while under the iteration bound.
+			base: MustNewDecFromStr("1.99999"),
 			exp:  MustNewDecFromStr("0.1"),
 		},
 	}