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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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/. */
+
+/* ECMAScript conversion operations. */
+
+#ifndef js_Conversions_h
+#define js_Conversions_h
+
+#include "mozilla/Casting.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/TypeTraits.h"
+
+#include <math.h>
+
+#include "jspubtd.h"
+
+#include "js/RootingAPI.h"
+#include "js/Value.h"
+
+struct JSContext;
+
+namespace js {
+
+/* DO NOT CALL THIS. Use JS::ToBoolean. */
+extern JS_PUBLIC_API(bool)
+ToBooleanSlow(JS::HandleValue v);
+
+/* DO NOT CALL THIS. Use JS::ToNumber. */
+extern JS_PUBLIC_API(bool)
+ToNumberSlow(JSContext* cx, JS::HandleValue v, double* dp);
+
+/* DO NOT CALL THIS. Use JS::ToInt8. */
+extern JS_PUBLIC_API(bool)
+ToInt8Slow(JSContext *cx, JS::HandleValue v, int8_t *out);
+
+/* DO NOT CALL THIS. Use JS::ToUint8. */
+extern JS_PUBLIC_API(bool)
+ToUint8Slow(JSContext *cx, JS::HandleValue v, uint8_t *out);
+
+/* DO NOT CALL THIS. Use JS::ToInt16. */
+extern JS_PUBLIC_API(bool)
+ToInt16Slow(JSContext *cx, JS::HandleValue v, int16_t *out);
+
+/* DO NOT CALL THIS. Use JS::ToInt32. */
+extern JS_PUBLIC_API(bool)
+ToInt32Slow(JSContext* cx, JS::HandleValue v, int32_t* out);
+
+/* DO NOT CALL THIS. Use JS::ToUint32. */
+extern JS_PUBLIC_API(bool)
+ToUint32Slow(JSContext* cx, JS::HandleValue v, uint32_t* out);
+
+/* DO NOT CALL THIS. Use JS::ToUint16. */
+extern JS_PUBLIC_API(bool)
+ToUint16Slow(JSContext* cx, JS::HandleValue v, uint16_t* out);
+
+/* DO NOT CALL THIS. Use JS::ToInt64. */
+extern JS_PUBLIC_API(bool)
+ToInt64Slow(JSContext* cx, JS::HandleValue v, int64_t* out);
+
+/* DO NOT CALL THIS. Use JS::ToUint64. */
+extern JS_PUBLIC_API(bool)
+ToUint64Slow(JSContext* cx, JS::HandleValue v, uint64_t* out);
+
+/* DO NOT CALL THIS. Use JS::ToString. */
+extern JS_PUBLIC_API(JSString*)
+ToStringSlow(JSContext* cx, JS::HandleValue v);
+
+/* DO NOT CALL THIS. Use JS::ToObject. */
+extern JS_PUBLIC_API(JSObject*)
+ToObjectSlow(JSContext* cx, JS::HandleValue v, bool reportScanStack);
+
+} // namespace js
+
+namespace JS {
+
+namespace detail {
+
+#ifdef JS_DEBUG
+/**
+ * Assert that we're not doing GC on cx, that we're in a request as
+ * needed, and that the compartments for cx and v are correct.
+ * Also check that GC would be safe at this point.
+ */
+extern JS_PUBLIC_API(void)
+AssertArgumentsAreSane(JSContext* cx, HandleValue v);
+#else
+inline void AssertArgumentsAreSane(JSContext* cx, HandleValue v)
+{}
+#endif /* JS_DEBUG */
+
+} // namespace detail
+
+/**
+ * ES6 draft 20141224, 7.1.1, second algorithm.
+ *
+ * Most users shouldn't call this -- use JS::ToBoolean, ToNumber, or ToString
+ * instead. This will typically only be called from custom convert hooks that
+ * wish to fall back to the ES6 default conversion behavior shared by most
+ * objects in JS, codified as OrdinaryToPrimitive.
+ */
+extern JS_PUBLIC_API(bool)
+OrdinaryToPrimitive(JSContext* cx, HandleObject obj, JSType type, MutableHandleValue vp);
+
+/* ES6 draft 20141224, 7.1.2. */
+MOZ_ALWAYS_INLINE bool
+ToBoolean(HandleValue v)
+{
+ if (v.isBoolean())
+ return v.toBoolean();
+ if (v.isInt32())
+ return v.toInt32() != 0;
+ if (v.isNullOrUndefined())
+ return false;
+ if (v.isDouble()) {
+ double d = v.toDouble();
+ return !mozilla::IsNaN(d) && d != 0;
+ }
+ if (v.isSymbol())
+ return true;
+
+ /* The slow path handles strings and objects. */
+ return js::ToBooleanSlow(v);
+}
+
+/* ES6 draft 20141224, 7.1.3. */
+MOZ_ALWAYS_INLINE bool
+ToNumber(JSContext* cx, HandleValue v, double* out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isNumber()) {
+ *out = v.toNumber();
+ return true;
+ }
+ return js::ToNumberSlow(cx, v, out);
+}
+
+/* ES6 draft 20141224, ToInteger (specialized for doubles). */
+inline double
+ToInteger(double d)
+{
+ if (d == 0)
+ return d;
+
+ if (!mozilla::IsFinite(d)) {
+ if (mozilla::IsNaN(d))
+ return 0;
+ return d;
+ }
+
+ return d < 0 ? ceil(d) : floor(d);
+}
+
+/* ES6 draft 20141224, 7.1.5. */
+MOZ_ALWAYS_INLINE bool
+ToInt32(JSContext* cx, JS::HandleValue v, int32_t* out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = v.toInt32();
+ return true;
+ }
+ return js::ToInt32Slow(cx, v, out);
+}
+
+/* ES6 draft 20141224, 7.1.6. */
+MOZ_ALWAYS_INLINE bool
+ToUint32(JSContext* cx, HandleValue v, uint32_t* out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = uint32_t(v.toInt32());
+ return true;
+ }
+ return js::ToUint32Slow(cx, v, out);
+}
+
+/* ES6 draft 20141224, 7.1.7. */
+MOZ_ALWAYS_INLINE bool
+ToInt16(JSContext *cx, JS::HandleValue v, int16_t *out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = int16_t(v.toInt32());
+ return true;
+ }
+ return js::ToInt16Slow(cx, v, out);
+}
+
+/* ES6 draft 20141224, 7.1.8. */
+MOZ_ALWAYS_INLINE bool
+ToUint16(JSContext* cx, HandleValue v, uint16_t* out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = uint16_t(v.toInt32());
+ return true;
+ }
+ return js::ToUint16Slow(cx, v, out);
+}
+
+/* ES6 draft 20141224, 7.1.9 */
+MOZ_ALWAYS_INLINE bool
+ToInt8(JSContext *cx, JS::HandleValue v, int8_t *out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = int8_t(v.toInt32());
+ return true;
+ }
+ return js::ToInt8Slow(cx, v, out);
+}
+
+/* ES6 ECMA-262, 7.1.10 */
+MOZ_ALWAYS_INLINE bool
+ToUint8(JSContext *cx, JS::HandleValue v, uint8_t *out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = uint8_t(v.toInt32());
+ return true;
+ }
+ return js::ToUint8Slow(cx, v, out);
+}
+
+/*
+ * Non-standard, with behavior similar to that of ToInt32, except in its
+ * producing an int64_t.
+ */
+MOZ_ALWAYS_INLINE bool
+ToInt64(JSContext* cx, HandleValue v, int64_t* out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = int64_t(v.toInt32());
+ return true;
+ }
+ return js::ToInt64Slow(cx, v, out);
+}
+
+/*
+ * Non-standard, with behavior similar to that of ToUint32, except in its
+ * producing a uint64_t.
+ */
+MOZ_ALWAYS_INLINE bool
+ToUint64(JSContext* cx, HandleValue v, uint64_t* out)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isInt32()) {
+ *out = uint64_t(v.toInt32());
+ return true;
+ }
+ return js::ToUint64Slow(cx, v, out);
+}
+
+/* ES6 draft 20141224, 7.1.12. */
+MOZ_ALWAYS_INLINE JSString*
+ToString(JSContext* cx, HandleValue v)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isString())
+ return v.toString();
+ return js::ToStringSlow(cx, v);
+}
+
+/* ES6 draft 20141224, 7.1.13. */
+inline JSObject*
+ToObject(JSContext* cx, HandleValue v)
+{
+ detail::AssertArgumentsAreSane(cx, v);
+
+ if (v.isObject())
+ return &v.toObject();
+ return js::ToObjectSlow(cx, v, false);
+}
+
+namespace detail {
+
+/*
+ * Convert a double value to ResultType (an unsigned integral type) using
+ * ECMAScript-style semantics (that is, in like manner to how ECMAScript's
+ * ToInt32 converts to int32_t).
+ *
+ * If d is infinite or NaN, return 0.
+ * Otherwise compute d2 = sign(d) * floor(abs(d)), and return the ResultType
+ * value congruent to d2 mod 2**(bit width of ResultType).
+ *
+ * The algorithm below is inspired by that found in
+ * <http://trac.webkit.org/changeset/67825/trunk/JavaScriptCore/runtime/JSValue.cpp>
+ * but has been generalized to all integer widths.
+ */
+template<typename ResultType>
+inline ResultType
+ToUintWidth(double d)
+{
+ static_assert(mozilla::IsUnsigned<ResultType>::value,
+ "ResultType must be an unsigned type");
+
+ uint64_t bits = mozilla::BitwiseCast<uint64_t>(d);
+ unsigned DoubleExponentShift = mozilla::FloatingPoint<double>::kExponentShift;
+
+ // Extract the exponent component. (Be careful here! It's not technically
+ // the exponent in NaN, infinities, and subnormals.)
+ int_fast16_t exp =
+ int_fast16_t((bits & mozilla::FloatingPoint<double>::kExponentBits) >> DoubleExponentShift) -
+ int_fast16_t(mozilla::FloatingPoint<double>::kExponentBias);
+
+ // If the exponent's less than zero, abs(d) < 1, so the result is 0. (This
+ // also handles subnormals.)
+ if (exp < 0)
+ return 0;
+
+ uint_fast16_t exponent = mozilla::AssertedCast<uint_fast16_t>(exp);
+
+ // If the exponent is greater than or equal to the bits of precision of a
+ // double plus ResultType's width, the number is either infinite, NaN, or
+ // too large to have lower-order bits in the congruent value. (Example:
+ // 2**84 is exactly representable as a double. The next exact double is
+ // 2**84 + 2**32. Thus if ResultType is int32_t, an exponent >= 84 implies
+ // floor(abs(d)) == 0 mod 2**32.) Return 0 in all these cases.
+ const size_t ResultWidth = CHAR_BIT * sizeof(ResultType);
+ if (exponent >= DoubleExponentShift + ResultWidth)
+ return 0;
+
+ // The significand contains the bits that will determine the final result.
+ // Shift those bits left or right, according to the exponent, to their
+ // locations in the unsigned binary representation of floor(abs(d)).
+ static_assert(sizeof(ResultType) <= sizeof(uint64_t),
+ "Left-shifting below would lose upper bits");
+ ResultType result = (exponent > DoubleExponentShift)
+ ? ResultType(bits << (exponent - DoubleExponentShift))
+ : ResultType(bits >> (DoubleExponentShift - exponent));
+
+ // Two further complications remain. First, |result| may contain bogus
+ // sign/exponent bits. Second, IEEE-754 numbers' significands (excluding
+ // subnormals, but we already handled those) have an implicit leading 1
+ // which may affect the final result.
+ //
+ // It may appear that there's complexity here depending on how ResultWidth
+ // and DoubleExponentShift relate, but it turns out there's not.
+ //
+ // Assume ResultWidth < DoubleExponentShift:
+ // Only right-shifts leave bogus bits in |result|. For this to happen,
+ // we must right-shift by > |DoubleExponentShift - ResultWidth|, implying
+ // |exponent < ResultWidth|.
+ // The implicit leading bit only matters if it appears in the final
+ // result -- if |2**exponent mod 2**ResultWidth != 0|. This implies
+ // |exponent < ResultWidth|.
+ // Otherwise assume ResultWidth >= DoubleExponentShift:
+ // Any left-shift less than |ResultWidth - DoubleExponentShift| leaves
+ // bogus bits in |result|. This implies |exponent < ResultWidth|. Any
+ // right-shift less than |ResultWidth| does too, which implies
+ // |DoubleExponentShift - ResultWidth < exponent|. By assumption, then,
+ // |exponent| is negative, but we excluded that above. So bogus bits
+ // need only |exponent < ResultWidth|.
+ // The implicit leading bit matters identically to the other case, so
+ // again, |exponent < ResultWidth|.
+ if (exponent < ResultWidth) {
+ ResultType implicitOne = ResultType(1) << exponent;
+ result &= implicitOne - 1; // remove bogus bits
+ result += implicitOne; // add the implicit bit
+ }
+
+ // Compute the congruent value in the signed range.
+ return (bits & mozilla::FloatingPoint<double>::kSignBit) ? ~result + 1 : result;
+}
+
+template<typename ResultType>
+inline ResultType
+ToIntWidth(double d)
+{
+ static_assert(mozilla::IsSigned<ResultType>::value,
+ "ResultType must be a signed type");
+
+ const ResultType MaxValue = (1ULL << (CHAR_BIT * sizeof(ResultType) - 1)) - 1;
+ const ResultType MinValue = -MaxValue - 1;
+
+ typedef typename mozilla::MakeUnsigned<ResultType>::Type UnsignedResult;
+ UnsignedResult u = ToUintWidth<UnsignedResult>(d);
+ if (u <= UnsignedResult(MaxValue))
+ return static_cast<ResultType>(u);
+ return (MinValue + static_cast<ResultType>(u - MaxValue)) - 1;
+}
+
+} // namespace detail
+
+/* ES5 9.5 ToInt32 (specialized for doubles). */
+inline int32_t
+ToInt32(double d)
+{
+ // clang crashes compiling this when targeting arm:
+ // https://llvm.org/bugs/show_bug.cgi?id=22974
+#if defined (__arm__) && defined (__GNUC__) && !defined(__clang__)
+ int32_t i;
+ uint32_t tmp0;
+ uint32_t tmp1;
+ uint32_t tmp2;
+ asm (
+ // We use a pure integer solution here. In the 'softfp' ABI, the argument
+ // will start in r0 and r1, and VFP can't do all of the necessary ECMA
+ // conversions by itself so some integer code will be required anyway. A
+ // hybrid solution is faster on A9, but this pure integer solution is
+ // notably faster for A8.
+
+ // %0 is the result register, and may alias either of the %[QR]1 registers.
+ // %Q4 holds the lower part of the mantissa.
+ // %R4 holds the sign, exponent, and the upper part of the mantissa.
+ // %1, %2 and %3 are used as temporary values.
+
+ // Extract the exponent.
+" mov %1, %R4, LSR #20\n"
+" bic %1, %1, #(1 << 11)\n" // Clear the sign.
+
+ // Set the implicit top bit of the mantissa. This clobbers a bit of the
+ // exponent, but we have already extracted that.
+" orr %R4, %R4, #(1 << 20)\n"
+
+ // Special Cases
+ // We should return zero in the following special cases:
+ // - Exponent is 0x000 - 1023: +/-0 or subnormal.
+ // - Exponent is 0x7ff - 1023: +/-INFINITY or NaN
+ // - This case is implicitly handled by the standard code path anyway,
+ // as shifting the mantissa up by the exponent will result in '0'.
+ //
+ // The result is composed of the mantissa, prepended with '1' and
+ // bit-shifted left by the (decoded) exponent. Note that because the r1[20]
+ // is the bit with value '1', r1 is effectively already shifted (left) by
+ // 20 bits, and r0 is already shifted by 52 bits.
+
+ // Adjust the exponent to remove the encoding offset. If the decoded
+ // exponent is negative, quickly bail out with '0' as such values round to
+ // zero anyway. This also catches +/-0 and subnormals.
+" sub %1, %1, #0xff\n"
+" subs %1, %1, #0x300\n"
+" bmi 8f\n"
+
+ // %1 = (decoded) exponent >= 0
+ // %R4 = upper mantissa and sign
+
+ // ---- Lower Mantissa ----
+" subs %3, %1, #52\n" // Calculate exp-52
+" bmi 1f\n"
+
+ // Shift r0 left by exp-52.
+ // Ensure that we don't overflow ARM's 8-bit shift operand range.
+ // We need to handle anything up to an 11-bit value here as we know that
+ // 52 <= exp <= 1024 (0x400). Any shift beyond 31 bits results in zero
+ // anyway, so as long as we don't touch the bottom 5 bits, we can use
+ // a logical OR to push long shifts into the 32 <= (exp&0xff) <= 255 range.
+" bic %2, %3, #0xff\n"
+" orr %3, %3, %2, LSR #3\n"
+ // We can now perform a straight shift, avoiding the need for any
+ // conditional instructions or extra branches.
+" mov %Q4, %Q4, LSL %3\n"
+" b 2f\n"
+"1:\n" // Shift r0 right by 52-exp.
+ // We know that 0 <= exp < 52, and we can shift up to 255 bits so 52-exp
+ // will always be a valid shift and we can sk%3 the range check for this case.
+" rsb %3, %1, #52\n"
+" mov %Q4, %Q4, LSR %3\n"
+
+ // %1 = (decoded) exponent
+ // %R4 = upper mantissa and sign
+ // %Q4 = partially-converted integer
+
+"2:\n"
+ // ---- Upper Mantissa ----
+ // This is much the same as the lower mantissa, with a few different
+ // boundary checks and some masking to hide the exponent & sign bit in the
+ // upper word.
+ // Note that the upper mantissa is pre-shifted by 20 in %R4, but we shift
+ // it left more to remove the sign and exponent so it is effectively
+ // pre-shifted by 31 bits.
+" subs %3, %1, #31\n" // Calculate exp-31
+" mov %1, %R4, LSL #11\n" // Re-use %1 as a temporary register.
+" bmi 3f\n"
+
+ // Shift %R4 left by exp-31.
+ // Avoid overflowing the 8-bit shift range, as before.
+" bic %2, %3, #0xff\n"
+" orr %3, %3, %2, LSR #3\n"
+ // Perform the shift.
+" mov %2, %1, LSL %3\n"
+" b 4f\n"
+"3:\n" // Shift r1 right by 31-exp.
+ // We know that 0 <= exp < 31, and we can shift up to 255 bits so 31-exp
+ // will always be a valid shift and we can skip the range check for this case.
+" rsb %3, %3, #0\n" // Calculate 31-exp from -(exp-31)
+" mov %2, %1, LSR %3\n" // Thumb-2 can't do "LSR %3" in "orr".
+
+ // %Q4 = partially-converted integer (lower)
+ // %R4 = upper mantissa and sign
+ // %2 = partially-converted integer (upper)
+
+"4:\n"
+ // Combine the converted parts.
+" orr %Q4, %Q4, %2\n"
+ // Negate the result if we have to, and move it to %0 in the process. To
+ // avoid conditionals, we can do this by inverting on %R4[31], then adding
+ // %R4[31]>>31.
+" eor %Q4, %Q4, %R4, ASR #31\n"
+" add %0, %Q4, %R4, LSR #31\n"
+" b 9f\n"
+"8:\n"
+ // +/-INFINITY, +/-0, subnormals, NaNs, and anything else out-of-range that
+ // will result in a conversion of '0'.
+" mov %0, #0\n"
+"9:\n"
+ : "=r" (i), "=&r" (tmp0), "=&r" (tmp1), "=&r" (tmp2), "=&r" (d)
+ : "4" (d)
+ : "cc"
+ );
+ return i;
+#else
+ return detail::ToIntWidth<int32_t>(d);
+#endif
+}
+
+/* ES5 9.6 (specialized for doubles). */
+inline uint32_t
+ToUint32(double d)
+{
+ return detail::ToUintWidth<uint32_t>(d);
+}
+
+/* WEBIDL 4.2.4 */
+inline int8_t
+ToInt8(double d)
+{
+ return detail::ToIntWidth<int8_t>(d);
+}
+
+/* ECMA-262 7.1.10 ToUInt8() specialized for doubles. */
+inline int8_t
+ToUint8(double d)
+{
+ return detail::ToUintWidth<uint8_t>(d);
+}
+
+/* WEBIDL 4.2.6 */
+inline int16_t
+ToInt16(double d)
+{
+ return detail::ToIntWidth<int16_t>(d);
+}
+
+inline uint16_t
+ToUint16(double d)
+{
+ return detail::ToUintWidth<uint16_t>(d);
+}
+
+/* WEBIDL 4.2.10 */
+inline int64_t
+ToInt64(double d)
+{
+ return detail::ToIntWidth<int64_t>(d);
+}
+
+/* WEBIDL 4.2.11 */
+inline uint64_t
+ToUint64(double d)
+{
+ return detail::ToUintWidth<uint64_t>(d);
+}
+
+} // namespace JS
+
+#endif /* js_Conversions_h */