improve number.AsRatio() conversion using stellar/go/price (#272), closes #264

Author: nikhilsaraf

model/number.go

@@ -5,6 +5,8 @@ import (
 	"log"
 	"math"
 	"strconv"
+
+	"github.com/stellar/go/price"
 )
 
 // NumberConstants holds some useful constants
@@ -39,32 +41,11 @@ func (n Number) AsString() string {
 
 // AsRatio returns an integer numerator and denominator
 func (n Number) AsRatio() (int32, int32, error) {
-	denominator64 := uint64(math.Pow(10, float64(n.Precision())))
-
-	var numerator64 uint64
-	// add an adjustment because the computed value should not have any digits beyond the decimal
-	// and we want to roll over values that are not computed correctly rather than using the expensive math/big library
-	unsignedPartial := n.AsFloat() * float64(denominator64)
-	if n.AsFloat() < 0 {
-		unsignedPartial *= -1
-	}
-	numerator64 = uint64(unsignedPartial + 0.1)
-
-	for numerator64%10 == 0 && denominator64 > 1 {
-		numerator64 /= 10
-		denominator64 /= 10
-	}
-
-	numerator, denominator := int32(numerator64), int32(denominator64)
-	if n.AsFloat() < 0 {
-		numerator *= -1
-	}
-
-	if float64(numerator)/float64(denominator) != n.AsFloat() {
-		return 0, 0, fmt.Errorf("invalid conversion to a ratio probably caused by an overflow, float input: %f, numerator: %d, denominator: %d", n.AsFloat(), numerator, denominator)
+	p, e := price.Parse(n.AsString())
+	if e != nil {
+		return 0, 0, fmt.Errorf("unable to convert number to ratio: %s", e)
 	}
-
-	return numerator, denominator, nil
+	return int32(p.N), int32(p.D), nil
 }
 
 // Abs returns the absolute of the number

model/number_test.go

@@ -289,12 +289,12 @@ func TestAsRatio(t *testing.T) {
 			wantD: 1000000,
 		}, {
 			n:     NumberFromFloat(5274.26, 8),
-			wantN: 527426,
-			wantD: 100,
+			wantN: 263713,
+			wantD: 50,
 		}, {
 			n:     NumberFromFloat(-5274.26, 8),
-			wantN: -527426,
-			wantD: 100,
+			wantN: -263713,
+			wantD: 50,
 		}, {
 			n:     NumberFromFloat(10.0, 4),
 			wantN: 10,
@@ -303,6 +303,10 @@ func TestAsRatio(t *testing.T) {
 			n:     NumberFromFloat(-10.0, 4),
 			wantN: -10,
 			wantD: 1,
+		}, {
+			n:     NumberFromFloat(2.599999999, 9),
+			wantN: 1039999997,
+			wantD: 399999999,
 		},
 	}
 
@@ -320,22 +324,3 @@ func TestAsRatio(t *testing.T) {
 		})
 	}
 }
-
-func TestAsRatio_Error(t *testing.T) {
-	testCases := []struct {
-		n *Number
-	}{
-		{
-			n: NumberFromFloat(2.599999999, 9),
-		},
-	}
-
-	for _, kase := range testCases {
-		t.Run(kase.n.AsString(), func(t *testing.T) {
-			num, den, e := kase.n.AsRatio()
-			if !assert.Error(t, e, fmt.Sprintf("got back num=%d, den=%d, expected an error", num, den)) {
-				return
-			}
-		})
-	}
-}