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diff --git a/Firestore/core/src/firebase/firestore/util/comparison.cc b/Firestore/core/src/firebase/firestore/util/comparison.cc
new file mode 100644
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+++ b/Firestore/core/src/firebase/firestore/util/comparison.cc
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+/*
+ * Copyright 2018 Google
+ *
+ * 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.
+ */
+
+#include "Firestore/core/src/firebase/firestore/util/comparison.h"
+
+#include <math.h>
+
+#include <limits>
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+bool Comparator<absl::string_view>::operator()(
+    const absl::string_view& left, const absl::string_view& right) const {
+  // TODO(wilhuff): truncation aware comparison
+  return left < right;
+}
+
+bool Comparator<double>::operator()(double left, double right) const {
+  // NaN sorts equal to itself and before any other number.
+  if (left < right) {
+    return true;
+  } else if (left >= right) {
+    return false;
+  } else {
+    // One or both left and right is NaN.
+    return isnan(left) && !isnan(right);
+  }
+}
+
+static constexpr double INT64_MIN_VALUE_AS_DOUBLE =
+    static_cast<double>(std::numeric_limits<int64_t>::min());
+
+static constexpr double INT64_MAX_VALUE_AS_DOUBLE =
+    static_cast<double>(std::numeric_limits<int64_t>::max());
+
+ComparisonResult CompareMixedNumber(double double_value, int64_t int64_value) {
+  // LLONG_MIN has an exact representation as double, so to check for a value
+  // outside the range representable by long, we have to check for strictly less
+  // than LLONG_MIN. Note that this also handles negative infinity.
+  if (double_value < INT64_MIN_VALUE_AS_DOUBLE) {
+    return ComparisonResult::Ascending;
+  }
+
+  // LLONG_MAX has no exact representation as double (casting as we've done
+  // makes 2^63, which is larger than LLONG_MAX), so consider any value greater
+  // than or equal to the threshold to be out of range. This also handles
+  // positive infinity.
+  if (double_value >= INT64_MAX_VALUE_AS_DOUBLE) {
+    return ComparisonResult::Descending;
+  }
+
+  // In Firestore NaN is defined to compare before all other numbers.
+  if (isnan(double_value)) {
+    return ComparisonResult::Ascending;
+  }
+
+  auto double_as_int64 = static_cast<int64_t>(double_value);
+  ComparisonResult cmp = Compare<int64_t>(double_as_int64, int64_value);
+  if (cmp != ComparisonResult::Same) {
+    return cmp;
+  }
+
+  // At this point the long representations are equal but this could be due to
+  // rounding.
+  double int64_as_double = static_cast<double>(int64_value);
+  return Compare<double>(double_value, int64_as_double);
+}
+
+/** Helper to normalize a double and then return the raw bits as a uint64_t. */
+uint64_t DoubleBits(double d) {
+  if (isnan(d)) {
+    d = NAN;
+  }
+
+  // Unlike C, C++ does not define type punning through a union type.
+
+  // TODO(wilhuff): replace with absl::bit_cast
+  static_assert(sizeof(double) == sizeof(uint64_t), "doubles must be 8 bytes");
+  uint64_t bits;
+  memcpy(&bits, &d, sizeof(bits));
+  return bits;
+}
+
+bool DoubleBitwiseEquals(double left, double right) {
+  return DoubleBits(left) == DoubleBits(right);
+}
+
+size_t DoubleBitwiseHash(double d) {
+  uint64_t bits = DoubleBits(d);
+  // Note that x ^ (x >> 32) works fine for both 32 and 64 bit definitions of
+  // size_t
+  return static_cast<size_t>(bits) ^ static_cast<size_t>(bits >> 32);
+}
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase