Decimal: add more tests

dec_arith.go

@@ -31,7 +31,7 @@ var pow10tab = [...]uint64{
 
 func pow10(n uint) Word { return Word(pow10tab[n]) }
 
-var maxDigits = [...]uint{
+var pow2digitsTab = [...]uint{
 	1, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 5,
 	5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10,
 	10, 10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 15,
@@ -49,15 +49,15 @@ func decDigits(x uint) (n uint) {
 }
 
 func decDigits64(x uint64) (n uint) {
-	n = maxDigits[bits.Len64(x)]
+	n = pow2digitsTab[bits.Len64(x)]
 	if x < uint64(pow10(n-1)) {
 		n--
 	}
 	return n
 }
 
 func decDigits32(x uint) (n uint) {
-	n = maxDigits[bits.Len(x)]
+	n = pow2digitsTab[bits.Len(x)]
 	if x < uint(pow10(n-1)) {
 		n--
 	}

dec_arith_test.go

@@ -517,3 +517,11 @@ func BenchmarkAddMul10VVW(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkShl10VU(b *testing.B) {
+	x := dec(rnd10V(1000))
+	z := dec(nil).make(1000)
+	for i := 0; i < b.N; i++ {
+		z.shl(x, 8)
+	}
+}

decimal_marsh_test.go

@@ -108,8 +108,8 @@ func TestDecimalCorruptGob(t *testing.T) {
 func TestDecimalJSONEncoding(t *testing.T) {
 	for _, test := range floatVals {
 		for _, sign := range []string{"", "+", "-"} {
-			for _, prec := range []uint{0, 1, 2, 10, 53, 64, 100, 1000} {
-				if prec > 53 && testing.Short() {
+			for _, prec := range []uint{0, 1, 2, 3, 19, 34, 300} {
+				if prec > 19 && testing.Short() {
 					continue
 				}
 				x := sign + test