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