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gecko-dev/js/public/Conversions.h

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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, 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/Compiler.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/WrappingOperations.h"
#include <cmath>
#include <stddef.h> // size_t
#include <stdint.h> // {u,}int{8,16,32,64}_t
#include <type_traits>
#include "jspubtd.h"
#include "jstypes.h" // JS_PUBLIC_API
#include "js/RootingAPI.h"
#include "js/Value.h"
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 !std::isnan(d) && d != 0;
}
if (v.isSymbol()) {
return true;
}
/* The slow path handles strings, BigInts 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);
}
// ES2020 draft rev 6b05bc56ba4e3c7a2b9922c4282d9eb844426d9b
// 7.1.5 ToInteger ( argument )
//
// Specialized for double values.
inline double ToInteger(double d) {
if (d == 0) {
return 0;
}
if (!std::isfinite(d)) {
if (std::isnan(d)) {
return 0;
}
return d;
}
return std::trunc(d) + (+0.0); // Add zero to convert -0 to +0.
}
/* 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);
}
#ifdef ENABLE_RECORD_TUPLE
inline JSObject* ToObjectOrGetObjectPayload(JSContext* cx, HandleValue v) {
detail::AssertArgumentsAreSane(cx, v);
if (v.hasObjectPayload()) {
return &v.getObjectPayload();
}
return js::ToObjectSlow(cx, v, false);
}
#endif
/**
* Convert a double value to UnsignedInteger (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
* UnsignedInteger value congruent to d2 % 2**(bit width of UnsignedInteger).
*
* The algorithm below is inspired by that found in
* <https://trac.webkit.org/changeset/67825/webkit/trunk/JavaScriptCore/runtime/JSValue.cpp>
* but has been generalized to all integer widths.
*/
template <typename UnsignedInteger>
inline UnsignedInteger ToUnsignedInteger(double d) {
static_assert(std::is_unsigned_v<UnsignedInteger>,
"UnsignedInteger 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 UnsignedInteger'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 UnsignedInteger is uint32_t, an exponent >= 84
// implies floor(abs(d)) == 0 mod 2**32.) Return 0 in all these cases.
constexpr size_t ResultWidth = CHAR_BIT * sizeof(UnsignedInteger);
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(UnsignedInteger) <= sizeof(uint64_t),
"left-shifting below would lose upper bits");
UnsignedInteger result =
(exponent > DoubleExponentShift)
? UnsignedInteger(bits << (exponent - DoubleExponentShift))
: UnsignedInteger(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) {
const auto implicitOne =
static_cast<UnsignedInteger>(UnsignedInteger{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 SignedInteger>
inline SignedInteger ToSignedInteger(double d) {
static_assert(std::is_signed_v<SignedInteger>,
"SignedInteger must be a signed type");
using UnsignedInteger = std::make_unsigned_t<SignedInteger>;
UnsignedInteger u = ToUnsignedInteger<UnsignedInteger>(d);
return mozilla::WrapToSigned(u);
}
// clang crashes compiling this when targeting arm:
// https://llvm.org/bugs/show_bug.cgi?id=22974
#if defined(__arm__) && MOZ_IS_GCC
template <>
inline int32_t ToSignedInteger<int32_t>(double d) {
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;
}
#endif // defined (__arm__) && MOZ_IS_GCC
namespace detail {
template <typename IntegerType,
bool IsUnsigned = std::is_unsigned_v<IntegerType>>
struct ToSignedOrUnsignedInteger;
template <typename IntegerType>
struct ToSignedOrUnsignedInteger<IntegerType, true> {
static IntegerType compute(double d) {
return ToUnsignedInteger<IntegerType>(d);
}
};
template <typename IntegerType>
struct ToSignedOrUnsignedInteger<IntegerType, false> {
static IntegerType compute(double d) {
return ToSignedInteger<IntegerType>(d);
}
};
} // namespace detail
template <typename IntegerType>
inline IntegerType ToSignedOrUnsignedInteger(double d) {
return detail::ToSignedOrUnsignedInteger<IntegerType>::compute(d);
}
/* WEBIDL 4.2.4 */
inline int8_t ToInt8(double d) { return ToSignedInteger<int8_t>(d); }
/* ECMA-262 7.1.10 ToUInt8() specialized for doubles. */
inline int8_t ToUint8(double d) { return ToUnsignedInteger<uint8_t>(d); }
/* WEBIDL 4.2.6 */
inline int16_t ToInt16(double d) { return ToSignedInteger<int16_t>(d); }
inline uint16_t ToUint16(double d) { return ToUnsignedInteger<uint16_t>(d); }
/* ES5 9.5 ToInt32 (specialized for doubles). */
inline int32_t ToInt32(double d) { return ToSignedInteger<int32_t>(d); }
/* ES5 9.6 (specialized for doubles). */
inline uint32_t ToUint32(double d) { return ToUnsignedInteger<uint32_t>(d); }
/* WEBIDL 4.2.10 */
inline int64_t ToInt64(double d) { return ToSignedInteger<int64_t>(d); }
/* WEBIDL 4.2.11 */
inline uint64_t ToUint64(double d) { return ToUnsignedInteger<uint64_t>(d); }
/**
* An amount of space large enough to store the null-terminated result of
* |ToString| on any Number.
*
* The <https://tc39.es/ecma262/#sec-tostring-applied-to-the-number-type>
* |NumberToString| algorithm is specified in terms of results, not an
* algorithm. It is extremely unclear from the algorithm's definition what its
* longest output can be. |-(2**-19 - 2**-72)| requires 25 + 1 characters and
* is believed to be at least *very close* to the upper bound, so we round that
* *very generously* upward to a 64-bit pointer-size boundary (to be extra
* cautious) and assume that's adequate.
*
* If you can supply better reasoning for a tighter bound, file a bug to improve
* this!
*/
static constexpr size_t MaximumNumberToStringLength = 31 + 1;
/**
* Store in |out| the null-terminated, base-10 result of |ToString| applied to
* |d| per <https://tc39.es/ecma262/#sec-tostring-applied-to-the-number-type>.
* (This will produce "NaN", "-Infinity", or "Infinity" for non-finite |d|.)
*/
extern JS_PUBLIC_API void NumberToString(
double d, char (&out)[MaximumNumberToStringLength]);
} // namespace JS
#endif /* js_Conversions_h */
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