first stab on checked ints

types/checked_ints.go

@@ -0,0 +1,33 @@
+package types
+
+import (
+	"errors"
+	"math"
+)
+
+var ErrOverflowInt = errors.New("integer overflow")
+
+type CheckedInt32 int32
+type CheckedUint32 uint32
+
+type CheckedInt64 int64
+type CheckedUint64 int64
+
+func (i32 CheckedInt32) CheckedAdd(otherI32 CheckedInt32) (CheckedInt32, error) {
+	if otherI32 > 0 && (i32 > math.MaxInt32-otherI32) {
+		return 0, ErrOverflowInt
+	} else if otherI32 < 0 && (i32 < math.MinInt32-otherI32) {
+		return 0, ErrOverflowInt
+	}
+	return i32 + otherI32, nil
+}
+
+func (i32 CheckedInt32) CheckedSub(otherI32 CheckedInt32) (CheckedInt32, error) {
+	if otherI32 > 0 && (i32 < math.MinInt32+otherI32) {
+		return 0, ErrOverflowInt
+	} else if otherI32 < 0 && (i32 > math.MaxInt32+otherI32) {
+		return 0, ErrOverflowInt
+	}
+	return i32 - otherI32, nil
+
+}

types/checked_ints_test.go

@@ -0,0 +1,61 @@
+package types
+
+import (
+	"math"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCheckedInt32_CheckedAdd(t *testing.T) {
+	tcs := []struct {
+		val1    int32
+		val2    int32
+		sum     int32
+		wantErr bool
+	}{
+		0: {math.MaxInt32, 1, 0, true},
+		1: {math.MinInt32, 1, math.MinInt32 + 1, false},
+		2: {math.MaxInt32, math.MaxInt32, 0, true},
+		3: {0, math.MaxInt32, math.MaxInt32, false},
+		4: {0, 1, 1, false},
+		5: {1, 1, 2, false},
+	}
+	for i, tc := range tcs {
+		v1 := CheckedInt32(tc.val1)
+		v2 := CheckedInt32(tc.val2)
+		sum, err := v1.CheckedAdd(v2)
+		if tc.wantErr {
+			assert.Error(t, err, "Should fail: %v", i)
+			assert.Zero(t, sum, "Got invalid sum for case %v", i)
+		} else {
+			assert.EqualValues(t, tc.sum, sum)
+		}
+	}
+}
+
+func TestCheckedInt32_CheckedSub(t *testing.T) {
+	tcs := []struct {
+		val1    int32
+		val2    int32
+		sum     int32
+		wantErr bool
+	}{
+		0: {math.MaxInt32, math.MaxInt32, 0, false},
+		1: {math.MinInt32, 1, 0, true},
+		2: {math.MinInt32 + 1, 1, math.MinInt32, false},
+		3: {1, 1, 0, false},
+		4: {1, 2, -1, false},
+	}
+	for i, tc := range tcs {
+		v1 := CheckedInt32(tc.val1)
+		v2 := CheckedInt32(tc.val2)
+		sum, err := v1.CheckedSub(v2)
+		if tc.wantErr {
+			assert.Error(t, err, "Should fail: %v", i)
+			assert.Zero(t, sum, "Got invalid sum for case %v", i)
+		} else {
+			assert.EqualValues(t, tc.sum, sum, "failed: %v", i)
+		}
+	}
+}