Add NewFromUint64 constructor (#352)

decimal.go

@@ -130,6 +130,18 @@ func NewFromInt32(value int32) Decimal {
 	}
 }
 
+// NewFromUint64 converts an uint64 to Decimal.
+//
+// Example:
+//
+//	NewFromUint64(123).String() // output: "123"
+func NewFromUint64(value uint64) Decimal {
+	return Decimal{
+		value: new(big.Int).SetUint64(value),
+		exp:   0,
+	}
+}
+
 // NewFromBigInt returns a new Decimal from a big.Int, value * 10 ^ exp
 func NewFromBigInt(value *big.Int, exp int32) Decimal {
 	return Decimal{

decimal_test.go

@@ -476,10 +476,11 @@ func TestNewFromFloatWithExponent(t *testing.T) {
 
 func TestNewFromInt(t *testing.T) {
 	tests := map[int64]string{
-		0:                   "0",
-		1:                   "1",
-		323412345:           "323412345",
-		9223372036854775807: "9223372036854775807",
+		0:                    "0",
+		1:                    "1",
+		323412345:            "323412345",
+		9223372036854775807:  "9223372036854775807",
+		-9223372036854775808: "-9223372036854775808",
 	}
 
 	// add negatives
@@ -501,10 +502,11 @@ func TestNewFromInt(t *testing.T) {
 
 func TestNewFromInt32(t *testing.T) {
 	tests := map[int32]string{
-		0:          "0",
-		1:          "1",
-		323412345:  "323412345",
-		2147483647: "2147483647",
+		0:           "0",
+		1:           "1",
+		323412345:   "323412345",
+		2147483647:  "2147483647",
+		-2147483648: "-2147483648",
 	}
 
 	// add negatives
@@ -524,6 +526,25 @@ func TestNewFromInt32(t *testing.T) {
 	}
 }
 
+func TestNewFromUint64(t *testing.T) {
+	tests := map[uint64]string{
+		0:                    "0",
+		1:                    "1",
+		323412345:            "323412345",
+		9223372036854775807:  "9223372036854775807",
+		18446744073709551615: "18446744073709551615",
+	}
+
+	for input, s := range tests {
+		d := NewFromUint64(input)
+		if d.String() != s {
+			t.Errorf("expected %s, got %s (%s, %d)",
+				s, d.String(),
+				d.value.String(), d.exp)
+		}
+	}
+}
+
 func TestNewFromBigIntWithExponent(t *testing.T) {
 	type Inp struct {
 		val *big.Int