diff -r 000000000000 -r 6474c204b198 dom/bindings/PrimitiveConversions.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/PrimitiveConversions.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,358 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
+/* vim: set ts=2 sw=2 et tw=79: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Conversions from jsval to primitive values
+ */
+
+#ifndef mozilla_dom_PrimitiveConversions_h
+#define mozilla_dom_PrimitiveConversions_h
+
+#include <limits>
+#include <math.h>
+#include <stdint.h>
+
+#include "jsapi.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/FloatingPoint.h"
+
+namespace mozilla {
+namespace dom {
+
+template<typename T>
+struct TypeName {
+};
+
+template<>
+struct TypeName<int8_t> {
+  static const char* value() {
+    return "byte";
+  }
+};
+template<>
+struct TypeName<uint8_t> {
+  static const char* value() {
+    return "octet";
+  }
+};
+template<>
+struct TypeName<int16_t> {
+  static const char* value() {
+    return "short";
+  }
+};
+template<>
+struct TypeName<uint16_t> {
+  static const char* value() {
+    return "unsigned short";
+  }
+};
+template<>
+struct TypeName<int32_t> {
+  static const char* value() {
+    return "long";
+  }
+};
+template<>
+struct TypeName<uint32_t> {
+  static const char* value() {
+    return "unsigned long";
+  }
+};
+template<>
+struct TypeName<int64_t> {
+  static const char* value() {
+    return "long long";
+  }
+};
+template<>
+struct TypeName<uint64_t> {
+  static const char* value() {
+    return "unsigned long long";
+  }
+};
+
+
+enum ConversionBehavior {
+  eDefault,
+  eEnforceRange,
+  eClamp
+};
+
+template<typename T, ConversionBehavior B>
+struct PrimitiveConversionTraits {
+};
+
+template<typename T>
+struct DisallowedConversion {
+  typedef int jstype;
+  typedef int intermediateType;
+
+private:
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    MOZ_CRASH("This should never be instantiated!");
+  }
+};
+
+struct PrimitiveConversionTraits_smallInt {
+  // The output of JS::ToInt32 is determined as follows:
+  //   1) The value is converted to a double
+  //   2) Anything that's not a finite double returns 0
+  //   3) The double is rounded towards zero to the nearest integer
+  //   4) The resulting integer is reduced mod 2^32.  The output of this
+  //      operation is an integer in the range [0, 2^32).
+  //   5) If the resulting number is >= 2^31, 2^32 is subtracted from it.
+  //
+  // The result of all this is a number in the range [-2^31, 2^31)
+  //
+  // WebIDL conversions for the 8-bit, 16-bit, and 32-bit integer types
+  // are defined in the same way, except that step 4 uses reduction mod
+  // 2^8 and 2^16 for the 8-bit and 16-bit types respectively, and step 5
+  // is only done for the signed types.
+  //
+  // C/C++ define integer conversion semantics to unsigned types as taking
+  // your input integer mod (1 + largest value representable in the
+  // unsigned type).  Since 2^32 is zero mod 2^8, 2^16, and 2^32,
+  // converting to the unsigned int of the relevant width will correctly
+  // perform step 4; in particular, the 2^32 possibly subtracted in step 5
+  // will become 0.
+  //
+  // Once we have step 4 done, we're just going to assume 2s-complement
+  // representation and cast directly to the type we really want.
+  //
+  // So we can cast directly for all unsigned types and for int32_t; for
+  // the smaller-width signed types we need to cast through the
+  // corresponding unsigned type.
+  typedef int32_t jstype;
+  typedef int32_t intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    return JS::ToInt32(cx, v, retval);
+  }
+};
+template<>
+struct PrimitiveConversionTraits<int8_t, eDefault> : PrimitiveConversionTraits_smallInt {
+  typedef uint8_t intermediateType;
+};
+template<>
+struct PrimitiveConversionTraits<uint8_t, eDefault> : PrimitiveConversionTraits_smallInt {
+};
+template<>
+struct PrimitiveConversionTraits<int16_t, eDefault> : PrimitiveConversionTraits_smallInt {
+  typedef uint16_t intermediateType;
+};
+template<>
+struct PrimitiveConversionTraits<uint16_t, eDefault> : PrimitiveConversionTraits_smallInt {
+};
+template<>
+struct PrimitiveConversionTraits<int32_t, eDefault> : PrimitiveConversionTraits_smallInt {
+};
+template<>
+struct PrimitiveConversionTraits<uint32_t, eDefault> : PrimitiveConversionTraits_smallInt {
+};
+
+template<>
+struct PrimitiveConversionTraits<int64_t, eDefault> {
+  typedef int64_t jstype;
+  typedef int64_t intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    return JS::ToInt64(cx, v, retval);
+  }
+};
+
+template<>
+struct PrimitiveConversionTraits<uint64_t, eDefault> {
+  typedef uint64_t jstype;
+  typedef uint64_t intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    return JS::ToUint64(cx, v, retval);
+  }
+};
+
+template<typename T>
+struct PrimitiveConversionTraits_Limits {
+  static inline T min() {
+    return std::numeric_limits<T>::min();
+  }
+  static inline T max() {
+    return std::numeric_limits<T>::max();
+  }
+};
+
+template<>
+struct PrimitiveConversionTraits_Limits<int64_t> {
+  static inline int64_t min() {
+    return -(1LL << 53);
+  }
+  static inline int64_t max() {
+    return (1LL << 53);
+  }
+};
+
+template<>
+struct PrimitiveConversionTraits_Limits<uint64_t> {
+  static inline uint64_t min() {
+    return 0;
+  }
+  static inline uint64_t max() {
+    return (1LL << 53);
+  }
+};
+
+template<typename T, bool (*Enforce)(JSContext* cx, const double& d, T* retval)>
+struct PrimitiveConversionTraits_ToCheckedIntHelper {
+  typedef T jstype;
+  typedef T intermediateType;
+
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    double intermediate;
+    if (!JS::ToNumber(cx, v, &intermediate)) {
+      return false;
+    }
+
+    return Enforce(cx, intermediate, retval);
+  }
+};
+
+template<typename T>
+inline bool
+PrimitiveConversionTraits_EnforceRange(JSContext* cx, const double& d, T* retval)
+{
+  static_assert(std::numeric_limits<T>::is_integer,
+                "This can only be applied to integers!");
+
+  if (!mozilla::IsFinite(d)) {
+    return ThrowErrorMessage(cx, MSG_ENFORCE_RANGE_NON_FINITE, TypeName<T>::value());
+  }
+
+  bool neg = (d < 0);
+  double rounded = floor(neg ? -d : d);
+  rounded = neg ? -rounded : rounded;
+  if (rounded < PrimitiveConversionTraits_Limits<T>::min() ||
+      rounded > PrimitiveConversionTraits_Limits<T>::max()) {
+    return ThrowErrorMessage(cx, MSG_ENFORCE_RANGE_OUT_OF_RANGE, TypeName<T>::value());
+  }
+
+  *retval = static_cast<T>(rounded);
+  return true;
+}
+
+template<typename T>
+struct PrimitiveConversionTraits<T, eEnforceRange> :
+  public PrimitiveConversionTraits_ToCheckedIntHelper<T, PrimitiveConversionTraits_EnforceRange<T> > {
+};
+
+template<typename T>
+inline bool
+PrimitiveConversionTraits_Clamp(JSContext* cx, const double& d, T* retval)
+{
+  static_assert(std::numeric_limits<T>::is_integer,
+                "This can only be applied to integers!");
+
+  if (mozilla::IsNaN(d)) {
+    *retval = 0;
+    return true;
+  }
+  if (d >= PrimitiveConversionTraits_Limits<T>::max()) {
+    *retval = PrimitiveConversionTraits_Limits<T>::max();
+    return true;
+  }
+  if (d <= PrimitiveConversionTraits_Limits<T>::min()) {
+    *retval = PrimitiveConversionTraits_Limits<T>::min();
+    return true;
+  }
+
+  MOZ_ASSERT(mozilla::IsFinite(d));
+
+  // Banker's rounding (round ties towards even).
+  // We move away from 0 by 0.5f and then truncate.  That gets us the right
+  // answer for any starting value except plus or minus N.5.  With a starting
+  // value of that form, we now have plus or minus N+1.  If N is odd, this is
+  // the correct result.  If N is even, plus or minus N is the correct result.
+  double toTruncate = (d < 0) ? d - 0.5 : d + 0.5;
+
+  T truncated = static_cast<T>(toTruncate);
+
+  if (truncated == toTruncate) {
+    /*
+     * It was a tie (since moving away from 0 by 0.5 gave us the exact integer
+     * we want). Since we rounded away from 0, we either already have an even
+     * number or we have an odd number but the number we want is one closer to
+     * 0. So just unconditionally masking out the ones bit should do the trick
+     * to get us the value we want.
+     */
+    truncated &= ~1;
+  }
+
+  *retval = truncated;
+  return true;
+}
+
+template<typename T>
+struct PrimitiveConversionTraits<T, eClamp> :
+  public PrimitiveConversionTraits_ToCheckedIntHelper<T, PrimitiveConversionTraits_Clamp<T> > {
+};
+
+
+template<ConversionBehavior B>
+struct PrimitiveConversionTraits<bool, B> : public DisallowedConversion<bool> {};
+
+template<>
+struct PrimitiveConversionTraits<bool, eDefault> {
+  typedef bool jstype;
+  typedef bool intermediateType;
+  static inline bool converter(JSContext* /* unused */, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    *retval = JS::ToBoolean(v);
+    return true;
+  }
+};
+
+
+template<ConversionBehavior B>
+struct PrimitiveConversionTraits<float, B> : public DisallowedConversion<float> {};
+
+template<ConversionBehavior B>
+struct PrimitiveConversionTraits<double, B> : public DisallowedConversion<double> {};
+
+struct PrimitiveConversionTraits_float {
+  typedef double jstype;
+  typedef double intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               jstype* retval) {
+    return JS::ToNumber(cx, v, retval);
+  }
+};
+
+template<>
+struct PrimitiveConversionTraits<float, eDefault> : PrimitiveConversionTraits_float {
+};
+template<>
+struct PrimitiveConversionTraits<double, eDefault> : PrimitiveConversionTraits_float {
+};
+
+
+template<typename T, ConversionBehavior B>
+bool ValueToPrimitive(JSContext* cx, JS::Handle<JS::Value> v, T* retval)
+{
+  typename PrimitiveConversionTraits<T, B>::jstype t;
+  if (!PrimitiveConversionTraits<T, B>::converter(cx, v, &t))
+    return false;
+
+  *retval = static_cast<T>(
+    static_cast<typename PrimitiveConversionTraits<T, B>::intermediateType>(t));
+  return true;
+}
+
+} // namespace dom
+} // namespace mozilla
+
+#endif /* mozilla_dom_PrimitiveConversions_h */