Fix precision loss in compareDoubleInt/compareDoubleUint for values outside float64 safe integer range

common/types/compare.go

@@ -16,32 +16,47 @@ package types
 
 import (
 	"math"
+	"math/big"
 
 	"github.com/google/cel-go/common/types/ref"
 )
 
+// compareDoubleInt compares a CEL double and int value for ordering purposes.
+//
+// Direct conversion of Int to float64 loses precision for integer values
+// outside the safe integer range of float64 (i.e., abs(i) > 2^53). Using
+// math/big.Float ensures an exact comparison without rounding errors.
 func compareDoubleInt(d Double, i Int) Int {
 	if d < math.MinInt64 {
 		return IntNegOne
 	}
 	if d > math.MaxInt64 {
 		return IntOne
 	}
-	return compareDouble(d, Double(i))
+	bf := new(big.Float).SetFloat64(float64(d))
+	bi := new(big.Float).SetInt64(int64(i))
+	return Int(bf.Cmp(bi))
 }
 
 func compareIntDouble(i Int, d Double) Int {
 	return -compareDoubleInt(d, i)
 }
 
+// compareDoubleUint compares a CEL double and uint value for ordering purposes.
+//
+// Direct conversion of Uint to float64 loses precision for values outside
+// the safe integer range of float64 (i.e., u > 2^53). Using math/big.Float
+// ensures an exact comparison without rounding errors.
 func compareDoubleUint(d Double, u Uint) Int {
 	if d < 0 {
 		return IntNegOne
 	}
 	if d > math.MaxUint64 {
 		return IntOne
 	}
-	return compareDouble(d, Double(u))
+	bf := new(big.Float).SetFloat64(float64(d))
+	bu := new(big.Float).SetUint64(uint64(u))
+	return Int(bf.Cmp(bu))
 }
 
 func compareUintDouble(u Uint, d Double) Int {

common/types/compare_test.go

@@ -0,0 +1,75 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package types
+
+import "testing"
+
+// TestCompareDoubleIntPrecision verifies that compareDoubleInt and
+// compareDoubleUint correctly distinguish integer values that are adjacent
+// to float64 representable boundaries (> 2^53), where naive float64 casting
+// loses precision and can incorrectly equate distinct integers.
+func TestCompareDoubleIntPrecision(t *testing.T) {
+	tests := []struct {
+		d    Double
+		i    Int
+		want Int
+		desc string
+	}{
+		// Values within safe float64 range — must still work correctly.
+		{Double(1.0), Int(1), IntZero, "1.0 == 1"},
+		{Double(1.5), Int(1), IntOne, "1.5 > 1"},
+		{Double(0.5), Int(1), IntNegOne, "0.5 < 1"},
+		{Double(9007199254740992), Int(9007199254740992), IntZero, "2^53 == 2^53"},
+
+		// Precision-loss zone (> 2^53): distinct integers must NOT compare equal.
+		// Bug: Double(i) cast loses low bits, collapsing adjacent ints to same float64.
+		{Double(9007199254740992), Int(9007199254740993), IntNegOne, "2^53 < 2^53+1"},
+		{Double(9007199254740992), Int(9007199254740994), IntNegOne, "2^53 < 2^53+2"},
+		{Double(1e17), Int(100000000000000001), IntNegOne, "1e17 < 1e17+1"},
+		{Double(1e18), Int(1000000000000000001), IntNegOne, "1e18 < 1e18+1"},
+
+		// Symmetric: int smaller than double.
+		{Double(9007199254740993), Int(9007199254740992), IntOne, "2^53+1 > 2^53 (as Double)"},
+	}
+	for _, tc := range tests {
+		got := compareDoubleInt(tc.d, tc.i)
+		if got != tc.want {
+			t.Errorf("compareDoubleInt(%v, %v): got %v, want %v — %s",
+				tc.d, tc.i, got, tc.want, tc.desc)
+		}
+	}
+}
+
+func TestCompareDoubleUintPrecision(t *testing.T) {
+	tests := []struct {
+		d    Double
+		u    Uint
+		want Int
+		desc string
+	}{
+		{Double(0), Uint(0), IntZero, "0.0 == 0"},
+		{Double(1.0), Uint(1), IntZero, "1.0 == 1"},
+		{Double(9007199254740992), Uint(9007199254740992), IntZero, "2^53 == 2^53"},
+		{Double(9007199254740992), Uint(9007199254740993), IntNegOne, "2^53 < 2^53+1 (uint)"},
+		{Double(1e17), Uint(100000000000000001), IntNegOne, "1e17 < 1e17+1 (uint)"},
+	}
+	for _, tc := range tests {
+		got := compareDoubleUint(tc.d, tc.u)
+		if got != tc.want {
+			t.Errorf("compareDoubleUint(%v, %v): got %v, want %v — %s",
+				tc.d, tc.u, got, tc.want, tc.desc)
+		}
+	}
+}