Add safe numerics classes, imported from Chromium

src/base/safe_conversions.h

Index: src/base/safe_conversions.h
diff --git a/src/base/safe_conversions.h b/src/base/safe_conversions.h
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+++ b/src/base/safe_conversions.h
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+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Slightly adapted for inclusion in V8.
+// Copyright 2014 the V8 project authors. All rights reserved.
+
+#ifndef V8_BASE_SAFE_CONVERSIONS_H_
+#define V8_BASE_SAFE_CONVERSIONS_H_
+
+#include <limits>
+
+#include "src/base/safe_conversions_impl.h"
+
+namespace v8 {
+namespace base {
+
+// Convenience function that returns true if the supplied value is in range
+// for the destination type.
+template <typename Dst, typename Src>
+inline bool IsValueInRangeForNumericType(Src value) {
+  return internal::DstRangeRelationToSrcRange<Dst>(value) ==
+         internal::RANGE_VALID;
+}
+
+// checked_cast<> is analogous to static_cast<> for numeric types,
+// except that it CHECKs that the specified numeric conversion will not
+// overflow or underflow. NaN source will always trigger a CHECK.
+template <typename Dst, typename Src>
+inline Dst checked_cast(Src value) {
+  CHECK(IsValueInRangeForNumericType<Dst>(value));
+  return static_cast<Dst>(value);
+}
+
+// saturated_cast<> is analogous to static_cast<> for numeric types, except
+// that the specified numeric conversion will saturate rather than overflow or
+// underflow. NaN assignment to an integral will trigger a CHECK condition.
+template <typename Dst, typename Src>
+inline Dst saturated_cast(Src value) {
+  // Optimization for floating point values, which already saturate.
+  if (std::numeric_limits<Dst>::is_iec559)
+    return static_cast<Dst>(value);
+
+  switch (internal::DstRangeRelationToSrcRange<Dst>(value)) {
+    case internal::RANGE_VALID:
+      return static_cast<Dst>(value);
+
+    case internal::RANGE_UNDERFLOW:
+      return std::numeric_limits<Dst>::min();
+
+    case internal::RANGE_OVERFLOW:
+      return std::numeric_limits<Dst>::max();
+
+    // Should fail only on attempting to assign NaN to a saturated integer.
+    case internal::RANGE_INVALID:
+      CHECK(false);
+      return std::numeric_limits<Dst>::max();
+  }
+
+  UNREACHABLE();
+  return static_cast<Dst>(value);
+}
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_SAFE_CONVERSIONS_H_