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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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,
/**
* 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 "js/Conversions.h"
#include "js/RootingAPI.h"
#include "mozilla/Assertions.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/dom/BindingCallContext.h"
namespace mozilla::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,
const char* sourceDescription, 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,
const char* sourceDescription, 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,
const char* sourceDescription, 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,
const char* sourceDescription, 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) + 1; }
static inline int64_t max() { return (1LL << 53) - 1; }
};
template <>
struct PrimitiveConversionTraits_Limits<uint64_t> {
static inline uint64_t min() { return 0; }
static inline uint64_t max() { return (1LL << 53) - 1; }
};
template <typename T, typename U,
bool (*Enforce)(U cx, const char* sourceDescription, const double& d,
T* retval)>
struct PrimitiveConversionTraits_ToCheckedIntHelper {
typedef T jstype;
typedef T intermediateType;
static inline bool converter(U cx, JS::Handle<JS::Value> v,
const char* sourceDescription, jstype* retval) {
double intermediate;
if (!JS::ToNumber(cx, v, &intermediate)) {
return false;
}
return Enforce(cx, sourceDescription, intermediate, retval);
}
};
template <typename T>
inline bool PrimitiveConversionTraits_EnforceRange(
BindingCallContext& cx, const char* sourceDescription, const double& d,
T* retval) {
static_assert(std::numeric_limits<T>::is_integer,
"This can only be applied to integers!");
if (!std::isfinite(d)) {
return cx.ThrowErrorMessage<MSG_ENFORCE_RANGE_NON_FINITE>(
sourceDescription, 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 cx.ThrowErrorMessage<MSG_ENFORCE_RANGE_OUT_OF_RANGE>(
sourceDescription, TypeName<T>::value());
}
*retval = static_cast<T>(rounded);
return true;
}
template <typename T>
struct PrimitiveConversionTraits<T, eEnforceRange>
: public PrimitiveConversionTraits_ToCheckedIntHelper<
T, BindingCallContext&, PrimitiveConversionTraits_EnforceRange<T> > {
};
template <typename T>
inline bool PrimitiveConversionTraits_Clamp(JSContext* cx,
const char* sourceDescription,
const double& d, T* retval) {
static_assert(std::numeric_limits<T>::is_integer,
"This can only be applied to integers!");
if (std::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(std::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, JSContext*, 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,
const char* sourceDescription, 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,
const char* sourceDescription, 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, typename U>
bool ValueToPrimitive(U& cx, JS::Handle<JS::Value> v,
const char* sourceDescription, T* retval) {
typename PrimitiveConversionTraits<T, B>::jstype t;
if (!PrimitiveConversionTraits<T, B>::converter(cx, v, sourceDescription, &t))
return false;
*retval = static_cast<T>(
static_cast<typename PrimitiveConversionTraits<T, B>::intermediateType>(
t));
return true;
}
} // namespace mozilla::dom
#endif /* mozilla_dom_PrimitiveConversions_h */