R4R: Sortable Decimal Bytes

types/decimal.go

@@ -551,6 +551,25 @@ func (d Dec) Ceil() Dec {
 
 //___________________________________________________________________________________
 
+// ValidSortableDec ensures that a Dec is within the sortable bounds,
+// a Dec can't have a precision of less than 10^-18.
+// Max sortable decimal was set to the reciprocal of SmallestDec.
+func ValidSortableDec(dec Dec) bool {
+	return dec.LTE(OneDec().Quo(SmallestDec()))
+}
+
+// SortableDecBytes returns a byte slice representation of a Dec that can be sorted.
+// Left and right pads with 0s so there are 18 digits to left and right of the decimal point.
+// For this reason, there is a maximum and minimum value for this, enforced by ValidSortableDec.
+func SortableDecBytes(dec Dec) []byte {
+	if !ValidSortableDec(dec) {
+		panic("dec must be within bounds")
+	}
+	return []byte(fmt.Sprintf(fmt.Sprintf("%%0%ds", Precision*2+1), dec.String()))
+}
+
+//___________________________________________________________________________________
+
 // reuse nil values
 var (
 	nilAmino string

types/decimal_test.go

@@ -443,3 +443,22 @@ func TestApproxSqrt(t *testing.T) {
 		require.Equal(t, tc.expected, res, "unexpected result for test case %d, input: %v", i, tc.input)
 	}
 }
+
+func TestDecSortableBytes(t *testing.T) {
+	tests := []struct {
+		d    Dec
+		want []byte
+	}{
+		{NewDec(0), []byte("000000000000000000.000000000000000000")},
+		{NewDec(1), []byte("000000000000000001.000000000000000000")},
+		{NewDec(10), []byte("000000000000000010.000000000000000000")},
+		{NewDec(12340), []byte("000000000000012340.000000000000000000")},
+		{NewDecWithPrec(12340, 4), []byte("000000000000000001.234000000000000000")},
+		{NewDecWithPrec(12340, 5), []byte("000000000000000000.123400000000000000")},
+		{NewDecWithPrec(12340, 8), []byte("000000000000000000.000123400000000000")},
+		{NewDecWithPrec(1009009009009009009, 17), []byte("000000000000000010.090090090090090090")},
+	}
+	for tcIndex, tc := range tests {
+		assert.Equal(t, tc.want, SortableDecBytes(tc.d), "bad String(), index: %v", tcIndex)
+	}
+}