/* -*- 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, * 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 #include #include #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 struct TypeName {}; template <> struct TypeName { static const char* value() { return "byte"; } }; template <> struct TypeName { static const char* value() { return "octet"; } }; template <> struct TypeName { static const char* value() { return "short"; } }; template <> struct TypeName { static const char* value() { return "unsigned short"; } }; template <> struct TypeName { static const char* value() { return "long"; } }; template <> struct TypeName { static const char* value() { return "unsigned long"; } }; template <> struct TypeName { static const char* value() { return "long long"; } }; template <> struct TypeName { static const char* value() { return "unsigned long long"; } }; enum ConversionBehavior { eDefault, eEnforceRange, eClamp }; template struct PrimitiveConversionTraits {}; template struct DisallowedConversion { typedef int jstype; typedef int intermediateType; private: static inline bool converter(JSContext* cx, JS::Handle 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 v, const char* sourceDescription, jstype* retval) { return JS::ToInt32(cx, v, retval); } }; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_smallInt { typedef uint8_t intermediateType; }; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_smallInt {}; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_smallInt { typedef uint16_t intermediateType; }; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_smallInt {}; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_smallInt {}; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_smallInt {}; template <> struct PrimitiveConversionTraits { typedef int64_t jstype; typedef int64_t intermediateType; static inline bool converter(JSContext* cx, JS::Handle v, const char* sourceDescription, jstype* retval) { return JS::ToInt64(cx, v, retval); } }; template <> struct PrimitiveConversionTraits { typedef uint64_t jstype; typedef uint64_t intermediateType; static inline bool converter(JSContext* cx, JS::Handle v, const char* sourceDescription, jstype* retval) { return JS::ToUint64(cx, v, retval); } }; template struct PrimitiveConversionTraits_Limits { static inline T min() { return std::numeric_limits::min(); } static inline T max() { return std::numeric_limits::max(); } }; template <> struct PrimitiveConversionTraits_Limits { static inline int64_t min() { return -(1LL << 53) + 1; } static inline int64_t max() { return (1LL << 53) - 1; } }; template <> struct PrimitiveConversionTraits_Limits { static inline uint64_t min() { return 0; } static inline uint64_t max() { return (1LL << 53) - 1; } }; template struct PrimitiveConversionTraits_ToCheckedIntHelper { typedef T jstype; typedef T intermediateType; static inline bool converter(U cx, JS::Handle v, const char* sourceDescription, jstype* retval) { double intermediate; if (!JS::ToNumber(cx, v, &intermediate)) { return false; } return Enforce(cx, sourceDescription, intermediate, retval); } }; template inline bool PrimitiveConversionTraits_EnforceRange( BindingCallContext& cx, const char* sourceDescription, const double& d, T* retval) { static_assert(std::numeric_limits::is_integer, "This can only be applied to integers!"); if (!mozilla::IsFinite(d)) { return cx.ThrowErrorMessage( sourceDescription, TypeName::value()); } bool neg = (d < 0); double rounded = floor(neg ? -d : d); rounded = neg ? -rounded : rounded; if (rounded < PrimitiveConversionTraits_Limits::min() || rounded > PrimitiveConversionTraits_Limits::max()) { return cx.ThrowErrorMessage( sourceDescription, TypeName::value()); } *retval = static_cast(rounded); return true; } template struct PrimitiveConversionTraits : public PrimitiveConversionTraits_ToCheckedIntHelper< T, BindingCallContext&, PrimitiveConversionTraits_EnforceRange > { }; template inline bool PrimitiveConversionTraits_Clamp(JSContext* cx, const char* sourceDescription, const double& d, T* retval) { static_assert(std::numeric_limits::is_integer, "This can only be applied to integers!"); if (mozilla::IsNaN(d)) { *retval = 0; return true; } if (d >= PrimitiveConversionTraits_Limits::max()) { *retval = PrimitiveConversionTraits_Limits::max(); return true; } if (d <= PrimitiveConversionTraits_Limits::min()) { *retval = PrimitiveConversionTraits_Limits::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(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 struct PrimitiveConversionTraits : public PrimitiveConversionTraits_ToCheckedIntHelper< T, JSContext*, PrimitiveConversionTraits_Clamp > {}; template struct PrimitiveConversionTraits : public DisallowedConversion { }; template <> struct PrimitiveConversionTraits { typedef bool jstype; typedef bool intermediateType; static inline bool converter(JSContext* /* unused */, JS::Handle v, const char* sourceDescription, jstype* retval) { *retval = JS::ToBoolean(v); return true; } }; template struct PrimitiveConversionTraits : public DisallowedConversion {}; template struct PrimitiveConversionTraits : public DisallowedConversion {}; struct PrimitiveConversionTraits_float { typedef double jstype; typedef double intermediateType; static inline bool converter(JSContext* cx, JS::Handle v, const char* sourceDescription, jstype* retval) { return JS::ToNumber(cx, v, retval); } }; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_float {}; template <> struct PrimitiveConversionTraits : PrimitiveConversionTraits_float {}; template bool ValueToPrimitive(U& cx, JS::Handle v, const char* sourceDescription, T* retval) { typename PrimitiveConversionTraits::jstype t; if (!PrimitiveConversionTraits::converter(cx, v, sourceDescription, &t)) return false; *retval = static_cast( static_cast::intermediateType>( t)); return true; } } // namespace mozilla::dom #endif /* mozilla_dom_PrimitiveConversions_h */