feat(math): add mutative api for Int.BigInt() (#17803)

math/CHANGELOG.md

@@ -36,6 +36,10 @@ Ref: https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.j
 
 ## [Unreleased]
 
+### Features
+
+* [#17803](https://github.com/cosmos/cosmos-sdk/pull/17803) Add mutative api for Int.BigInt()
+
 ### Bug Fixes
 
 * [#17725](https://github.com/cosmos/cosmos-sdk/pull/17725) Fix state break in ApproxRoot. This has been present since math/v1.0.1. It changed the rounding behavior at precision end in an intermediary division from banker's to truncation. The truncation occurs from binary right shift in the case of square roots. The change is now reverted back to banker's rounding universally for any root.

math/int.go

@@ -86,6 +86,14 @@ func (i Int) BigInt() *big.Int {
 	return new(big.Int).Set(i.i)
 }
 
+// BigInt converts Int to big.Int, mutative the input
+func (i Int) BigIntMut() *big.Int {
+	if i.IsNil() {
+		return nil
+	}
+	return i.i
+}
+
 // IsNil returns true if Int is uninitialized
 func (i Int) IsNil() bool {
 	return i.i == nil

math/int_test.go

@@ -56,6 +56,26 @@ func (s *intTestSuite) TestNewIntFromBigInt() {
 	s.Require().NotEqual(r, i.BigInt())
 }
 
+func (s *intTestSuite) TestConvertToBigIntMutative() {
+	r := big.NewInt(42)
+	i := math.NewIntFromBigInt(r)
+
+	// Compare value of BigInt & BigIntMut
+	s.Require().Equal(i.BigInt(), i.BigIntMut())
+
+	// Modify BigIntMut() pointer and ensure i.BigIntMut() & i.BigInt() change
+	p := i.BigIntMut()
+	p.SetInt64(50)
+	s.Require().Equal(big.NewInt(50), i.BigIntMut())
+	s.Require().Equal(big.NewInt(50), i.BigInt())
+
+	// Modify big.Int() pointer and ensure i.BigIntMut() & i.BigInt() don't change
+	p = i.BigInt()
+	p.SetInt64(60)
+	s.Require().NotEqual(big.NewInt(60), i.BigIntMut())
+	s.Require().NotEqual(big.NewInt(60), i.BigInt())
+}
+
 func (s *intTestSuite) TestIntPanic() {
 	// Max Int = 2^256-1 = 1.1579209e+77
 	// Min Int = -(2^256-1) = -1.1579209e+77