Use signaling NaN for holes in fixed double arrays.

src/base/math.cc

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/base/macros.h"
+#include "src/base/math.h"
+
+namespace v8 {
+namespace base {
+
+bool IsQuietNaN(float x) {
+  uint32_t const v = bit_cast<uint32_t>(x);
+  return (v >= 0x7FC00000u && v <= 0x7FFFFFFFu) || v >= 0xFFC00000u;
+}
+
+
+bool IsQuietNaN(double x) {
+  uint32_t const v = bit_cast<uint64_t>(x) >> 32u;
+  return (v >= 0x7FF80000u && v <= 0x7FFFFFFFu) || v >= 0xFFF80000u;
+}
+
+
+bool IsSignalingNaN(float x) {
+  uint32_t const v = bit_cast<uint32_t>(x);
+  return (v >= 0x7F800001u && v <= 0x7FBFFFFFu) ||
+         (v >= 0xFF800001u && v <= 0xFFBFFFFFu);
+}
+
+
+bool IsSignalingNaN(double x) {
+  uint64_t const v = bit_cast<uint64_t>(x);
+  return (v >= V8_UINT64_C(0x7FF0000000000001) &&
+          v <= V8_UINT64_C(0x7FF7FFFFFFFFFFFF)) ||
+         (v >= V8_UINT64_C(0xFFF0000000000001) &&
+          v <= V8_UINT64_C(0xFFF7FFFFFFFFFFFF));
+}
+
+}  // namespace base
+}  // namespace v8