strconv: fix ParseUint return value on range overflow

If the value corresponding to the input string cannot be
represented by an unsigned integer of the given size,
err.Err = ErrRange and the returned value is the maximum
magnitude unsigned integer of the appropriate bitSize.
This is consistent with ParseInt's behavior and the documentation.

Expand tests to test 32 bit test value tables with bitsize 32 set.
These tests fail without the fix in this CL.

Fixes #21278

Change-Id: I8aab39279ec3e31905fcbf582a916cbf6d9b95da
Reviewed-on: https://go-review.googlesource.com/55134
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

src/strconv/atoi.go

@@ -115,7 +115,7 @@ func ParseUint(s string, base int, bitSize int) (uint64, error) {
 
 		if n >= cutoff {
 			// n*base overflows
-			n = maxUint64
+			n = maxVal
 			err = ErrRange
 			goto Error
 		}
@@ -124,7 +124,7 @@ func ParseUint(s string, base int, bitSize int) (uint64, error) {
 		n1 := n + uint64(v)
 		if n1 < n || n1 > maxVal {
 			// n+v overflows
-			n = maxUint64
+			n = maxVal
 			err = ErrRange
 			goto Error
 		}

src/strconv/atoi_test.go

@@ -235,6 +235,17 @@ func init() {
 	}
 }
 
+func TestParseUint32(t *testing.T) {
+	for i := range atoui32tests {
+		test := &atoui32tests[i]
+		out, err := ParseUint(test.in, 10, 32)
+		if uint64(test.out) != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("Atoui32(%q) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+	}
+}
+
 func TestParseUint64(t *testing.T) {
 	for i := range atoui64tests {
 		test := &atoui64tests[i]
@@ -257,6 +268,17 @@ func TestParseUint64Base(t *testing.T) {
 	}
 }
 
+func TestParseInt32(t *testing.T) {
+	for i := range atoi32tests {
+		test := &atoi32tests[i]
+		out, err := ParseInt(test.in, 10, 32)
+		if int64(test.out) != out || !reflect.DeepEqual(test.err, err) {
+			t.Errorf("Atoi32(%q) = %v, %v want %v, %v",
+				test.in, out, err, test.out, test.err)
+		}
+	}
+}
+
 func TestParseInt64(t *testing.T) {
 	for i := range atoi64tests {
 		test := &atoi64tests[i]