add rounding tests

util/bpmath/bp.go

@@ -4,12 +4,22 @@ import (
 	"math"
 
 	cmath "cosmossdk.io/math"
+	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
 // BP represents values in basis points. Maximum value is 2^32-1.
 // Note: BP operations should not be chained - this causes precision losses.
 type BP uint32
 
+func (bp BP) ToDec() sdk.Dec {
+	return sdk.NewDecWithPrec(int64(bp), 4)
+}
+
+// Mul return a*bp rounding towards zero.
+func (bp BP) Mul(a cmath.Int) cmath.Int {
+	return Mul(a, bp)
+}
+
 // FromQuo returns a/b in basis points.
 // Contract: a>=0 and b > 0.
 // Panics if a/b >= MaxUint32/10'000 or if b==0.
@@ -32,7 +42,7 @@ func quo(a, b cmath.Int, rounding Rounding, max uint64) uint64 {
 	return x
 }
 
-// Mul returns a * b_basis_points
+// Mul returns a * b_basis_points rounding towards zero.
 // Contract: b in [0, MaxUint32]
 func Mul[T BP | FixedBP](a cmath.Int, b T) cmath.Int {
 	if b == 0 {
@@ -43,7 +53,3 @@ func Mul[T BP | FixedBP](a cmath.Int, b T) cmath.Int {
 	}
 	return a.MulRaw(int64(b)).Quo(oneBigInt)
 }
-
-func (bp BP) ToDec() cmath.LegacyDec {
-	return cmath.LegacyNewDecWithPrec(int64(bp), 4)
-}

util/bpmath/bp_test.go

@@ -45,4 +45,14 @@ func TestInt(t *testing.T) {
 	require.Equal(sresult, sdk.NewInt(12))
 	mresult = Mul(mi, bp)
 	require.Equal(mresult, math.NewInt(12))
+
+	// test rounding
+	si = sdk.NewInt(1299)
+	require.Equal(bp.Mul(si), sdk.NewInt(12))
+
+	si = sdk.NewInt(-1299)
+	require.Equal(bp.Mul(si), sdk.NewInt(-12))
+
+	si = sdk.NewInt(-1201)
+	require.Equal(bp.Mul(si), sdk.NewInt(-12))
 }

util/bpmath/doc.go

@@ -1,4 +1,4 @@
-// Package bpmath provides types and functions for doing basis point operations.
-// There is no precision lost for operations like `a * b` where `a` or `b` is basis points,
-// and the other variable is `Int`.
+// Package bpmath provides types and functions for doing basis point operations with math.Int.
+// So, the result is always math.Int, and follows the Go rounding semantic for integer nubmer:
+// rounds towards zero.
 package bpmath

util/bpmath/fixed_bp.go

@@ -2,6 +2,7 @@ package bpmath
 
 import (
 	"cosmossdk.io/math"
+	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
 // FixedBP assures that all operations are in 0-10'000 range
@@ -15,6 +16,11 @@ func FixedFromQuo(dividend, divisor math.Int, rounding Rounding) FixedBP {
 	return FixedBP(quo(dividend, divisor, rounding, One))
 }
 
-func (bp FixedBP) ToDec() math.LegacyDec {
-	return math.LegacyNewDecWithPrec(int64(bp), 4)
+func (bp FixedBP) ToDec() sdk.Dec {
+	return sdk.NewDecWithPrec(int64(bp), 4)
+}
+
+// Mul return a*bp rounding towards zero.
+func (bp FixedBP) Mul(a math.Int) math.Int {
+	return Mul(a, bp)
 }