зеркало из https://github.com/mozilla/gecko-dev.git
502 строки
16 KiB
C++
502 строки
16 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sts=4 et sw=4 tw=99:
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* ECMAScript conversion operations. */
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#ifndef js_Conversions_h
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#define js_Conversions_h
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#include "mozilla/Casting.h"
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#include "mozilla/FloatingPoint.h"
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#include "mozilla/TypeTraits.h"
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#include <math.h>
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#include "jspubtd.h"
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#include "js/RootingAPI.h"
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#include "js/Value.h"
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struct JSContext;
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namespace js {
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/* DO NOT CALL THIS. Use JS::ToBoolean. */
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extern JS_PUBLIC_API(bool)
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ToBooleanSlow(JS::HandleValue v);
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/* DO NOT CALL THIS. Use JS::ToNumber. */
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extern JS_PUBLIC_API(bool)
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ToNumberSlow(JSContext* cx, JS::Value v, double* dp);
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/* DO NOT CALL THIS. Use JS::ToInt32. */
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extern JS_PUBLIC_API(bool)
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ToInt32Slow(JSContext* cx, JS::HandleValue v, int32_t* out);
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/* DO NOT CALL THIS. Use JS::ToUint32. */
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extern JS_PUBLIC_API(bool)
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ToUint32Slow(JSContext* cx, JS::HandleValue v, uint32_t* out);
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/* DO NOT CALL THIS. Use JS::ToUint16. */
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extern JS_PUBLIC_API(bool)
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ToUint16Slow(JSContext* cx, JS::HandleValue v, uint16_t* out);
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/* DO NOT CALL THIS. Use JS::ToInt64. */
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extern JS_PUBLIC_API(bool)
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ToInt64Slow(JSContext* cx, JS::HandleValue v, int64_t* out);
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/* DO NOT CALL THIS. Use JS::ToUint64. */
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extern JS_PUBLIC_API(bool)
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ToUint64Slow(JSContext* cx, JS::HandleValue v, uint64_t* out);
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/* DO NOT CALL THIS. Use JS::ToString. */
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extern JS_PUBLIC_API(JSString*)
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ToStringSlow(JSContext* cx, JS::HandleValue v);
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/* DO NOT CALL THIS. Use JS::ToObject. */
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extern JS_PUBLIC_API(JSObject*)
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ToObjectSlow(JSContext* cx, JS::HandleValue v, bool reportScanStack);
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} // namespace js
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namespace JS {
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namespace detail {
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#ifdef JS_DEBUG
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/*
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* Assert that we're not doing GC on cx, that we're in a request as
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* needed, and that the compartments for cx and v are correct.
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* Also check that GC would be safe at this point.
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*/
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extern JS_PUBLIC_API(void)
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AssertArgumentsAreSane(JSContext* cx, HandleValue v);
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#else
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inline void AssertArgumentsAreSane(JSContext* cx, HandleValue v)
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{}
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#endif /* JS_DEBUG */
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} // namespace detail
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/*
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* ES6 draft 20141224, 7.1.1, second algorithm.
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*
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* Most users shouldn't call this -- use JS::ToBoolean, ToNumber, or ToString
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* instead. This will typically only be called from custom convert hooks that
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* wish to fall back to the ES6 default conversion behavior shared by most
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* objects in JS, codified as OrdinaryToPrimitive.
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*/
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extern JS_PUBLIC_API(bool)
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OrdinaryToPrimitive(JSContext* cx, HandleObject obj, JSType type, MutableHandleValue vp);
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/* ES6 draft 20141224, 7.1.2. */
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MOZ_ALWAYS_INLINE bool
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ToBoolean(HandleValue v)
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{
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if (v.isBoolean())
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return v.toBoolean();
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if (v.isInt32())
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return v.toInt32() != 0;
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if (v.isNullOrUndefined())
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return false;
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if (v.isDouble()) {
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double d = v.toDouble();
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return !mozilla::IsNaN(d) && d != 0;
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}
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if (v.isSymbol())
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return true;
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/* The slow path handles strings and objects. */
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return js::ToBooleanSlow(v);
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}
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/* ES6 draft 20141224, 7.1.3. */
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MOZ_ALWAYS_INLINE bool
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ToNumber(JSContext* cx, HandleValue v, double* out)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isNumber()) {
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*out = v.toNumber();
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return true;
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}
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return js::ToNumberSlow(cx, v, out);
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}
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/* ES6 draft 20141224, ToInteger (specialized for doubles). */
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inline double
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ToInteger(double d)
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{
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if (d == 0)
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return d;
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if (!mozilla::IsFinite(d)) {
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if (mozilla::IsNaN(d))
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return 0;
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return d;
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}
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return d < 0 ? ceil(d) : floor(d);
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}
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/* ES6 draft 20141224, 7.1.5. */
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MOZ_ALWAYS_INLINE bool
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ToInt32(JSContext* cx, JS::HandleValue v, int32_t* out)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isInt32()) {
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*out = v.toInt32();
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return true;
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}
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return js::ToInt32Slow(cx, v, out);
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}
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/* ES6 draft 20141224, 7.1.6. */
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MOZ_ALWAYS_INLINE bool
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ToUint32(JSContext* cx, HandleValue v, uint32_t* out)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isInt32()) {
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*out = uint32_t(v.toInt32());
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return true;
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}
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return js::ToUint32Slow(cx, v, out);
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}
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/* ES6 draft 20141224, 7.1.8. */
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MOZ_ALWAYS_INLINE bool
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ToUint16(JSContext* cx, HandleValue v, uint16_t* out)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isInt32()) {
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*out = uint16_t(v.toInt32());
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return true;
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}
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return js::ToUint16Slow(cx, v, out);
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}
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/*
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* Non-standard, with behavior similar to that of ToInt32, except in its
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* producing an int64_t.
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*/
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MOZ_ALWAYS_INLINE bool
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ToInt64(JSContext* cx, HandleValue v, int64_t* out)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isInt32()) {
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*out = int64_t(v.toInt32());
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return true;
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}
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return js::ToInt64Slow(cx, v, out);
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}
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/*
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* Non-standard, with behavior similar to that of ToUint32, except in its
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* producing a uint64_t.
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*/
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MOZ_ALWAYS_INLINE bool
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ToUint64(JSContext* cx, HandleValue v, uint64_t* out)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isInt32()) {
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*out = uint64_t(v.toInt32());
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return true;
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}
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return js::ToUint64Slow(cx, v, out);
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}
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/* ES6 draft 20141224, 7.1.12. */
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MOZ_ALWAYS_INLINE JSString*
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ToString(JSContext* cx, HandleValue v)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isString())
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return v.toString();
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return js::ToStringSlow(cx, v);
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}
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/* ES6 draft 20141224, 7.1.13. */
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inline JSObject*
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ToObject(JSContext* cx, HandleValue v)
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{
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detail::AssertArgumentsAreSane(cx, v);
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if (v.isObject())
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return &v.toObject();
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return js::ToObjectSlow(cx, v, false);
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}
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namespace detail {
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/*
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* Convert a double value to ResultType (an unsigned integral type) using
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* ECMAScript-style semantics (that is, in like manner to how ECMAScript's
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* ToInt32 converts to int32_t).
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*
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* If d is infinite or NaN, return 0.
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* Otherwise compute d2 = sign(d) * floor(abs(d)), and return the ResultType
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* value congruent to d2 mod 2**(bit width of ResultType).
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*
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* The algorithm below is inspired by that found in
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* <http://trac.webkit.org/changeset/67825/trunk/JavaScriptCore/runtime/JSValue.cpp>
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* but has been generalized to all integer widths.
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*/
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template<typename ResultType>
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inline ResultType
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ToUintWidth(double d)
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{
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static_assert(mozilla::IsUnsigned<ResultType>::value,
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"ResultType must be an unsigned type");
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uint64_t bits = mozilla::BitwiseCast<uint64_t>(d);
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unsigned DoubleExponentShift = mozilla::FloatingPoint<double>::kExponentShift;
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// Extract the exponent component. (Be careful here! It's not technically
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// the exponent in NaN, infinities, and subnormals.)
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int_fast16_t exp =
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int_fast16_t((bits & mozilla::FloatingPoint<double>::kExponentBits) >> DoubleExponentShift) -
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int_fast16_t(mozilla::FloatingPoint<double>::kExponentBias);
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// If the exponent's less than zero, abs(d) < 1, so the result is 0. (This
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// also handles subnormals.)
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if (exp < 0)
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return 0;
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uint_fast16_t exponent = mozilla::AssertedCast<uint_fast16_t>(exp);
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// If the exponent is greater than or equal to the bits of precision of a
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// double plus ResultType's width, the number is either infinite, NaN, or
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// too large to have lower-order bits in the congruent value. (Example:
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// 2**84 is exactly representable as a double. The next exact double is
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// 2**84 + 2**32. Thus if ResultType is int32_t, an exponent >= 84 implies
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// floor(abs(d)) == 0 mod 2**32.) Return 0 in all these cases.
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const size_t ResultWidth = CHAR_BIT * sizeof(ResultType);
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if (exponent >= DoubleExponentShift + ResultWidth)
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return 0;
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// The significand contains the bits that will determine the final result.
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// Shift those bits left or right, according to the exponent, to their
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// locations in the unsigned binary representation of floor(abs(d)).
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static_assert(sizeof(ResultType) <= sizeof(uint64_t),
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"Left-shifting below would lose upper bits");
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ResultType result = (exponent > DoubleExponentShift)
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? ResultType(bits << (exponent - DoubleExponentShift))
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: ResultType(bits >> (DoubleExponentShift - exponent));
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// Two further complications remain. First, |result| may contain bogus
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// sign/exponent bits. Second, IEEE-754 numbers' significands (excluding
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// subnormals, but we already handled those) have an implicit leading 1
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// which may affect the final result.
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//
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// It may appear that there's complexity here depending on how ResultWidth
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// and DoubleExponentShift relate, but it turns out there's not.
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//
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// Assume ResultWidth < DoubleExponentShift:
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// Only right-shifts leave bogus bits in |result|. For this to happen,
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// we must right-shift by > |DoubleExponentShift - ResultWidth|, implying
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// |exponent < ResultWidth|.
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// The implicit leading bit only matters if it appears in the final
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// result -- if |2**exponent mod 2**ResultWidth != 0|. This implies
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// |exponent < ResultWidth|.
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// Otherwise assume ResultWidth >= DoubleExponentShift:
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// Any left-shift less than |ResultWidth - DoubleExponentShift| leaves
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// bogus bits in |result|. This implies |exponent < ResultWidth|. Any
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// right-shift less than |ResultWidth| does too, which implies
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// |DoubleExponentShift - ResultWidth < exponent|. By assumption, then,
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// |exponent| is negative, but we excluded that above. So bogus bits
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// need only |exponent < ResultWidth|.
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// The implicit leading bit matters identically to the other case, so
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// again, |exponent < ResultWidth|.
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if (exponent < ResultWidth) {
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ResultType implicitOne = ResultType(1) << exponent;
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result &= implicitOne - 1; // remove bogus bits
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result += implicitOne; // add the implicit bit
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}
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// Compute the congruent value in the signed range.
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return (bits & mozilla::FloatingPoint<double>::kSignBit) ? ~result + 1 : result;
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}
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template<typename ResultType>
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inline ResultType
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ToIntWidth(double d)
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{
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static_assert(mozilla::IsSigned<ResultType>::value,
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"ResultType must be a signed type");
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const ResultType MaxValue = (1ULL << (CHAR_BIT * sizeof(ResultType) - 1)) - 1;
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const ResultType MinValue = -MaxValue - 1;
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typedef typename mozilla::MakeUnsigned<ResultType>::Type UnsignedResult;
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UnsignedResult u = ToUintWidth<UnsignedResult>(d);
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if (u <= UnsignedResult(MaxValue))
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return static_cast<ResultType>(u);
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return (MinValue + static_cast<ResultType>(u - MaxValue)) - 1;
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}
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} // namespace detail
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/* ES5 9.5 ToInt32 (specialized for doubles). */
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inline int32_t
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ToInt32(double d)
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{
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#if defined (__arm__) && defined (__GNUC__)
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int32_t i;
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uint32_t tmp0;
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uint32_t tmp1;
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uint32_t tmp2;
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asm (
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// We use a pure integer solution here. In the 'softfp' ABI, the argument
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// will start in r0 and r1, and VFP can't do all of the necessary ECMA
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// conversions by itself so some integer code will be required anyway. A
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// hybrid solution is faster on A9, but this pure integer solution is
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// notably faster for A8.
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// %0 is the result register, and may alias either of the %[QR]1 registers.
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// %Q4 holds the lower part of the mantissa.
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// %R4 holds the sign, exponent, and the upper part of the mantissa.
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// %1, %2 and %3 are used as temporary values.
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// Extract the exponent.
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" mov %1, %R4, LSR #20\n"
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" bic %1, %1, #(1 << 11)\n" // Clear the sign.
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// Set the implicit top bit of the mantissa. This clobbers a bit of the
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// exponent, but we have already extracted that.
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" orr %R4, %R4, #(1 << 20)\n"
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// Special Cases
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// We should return zero in the following special cases:
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// - Exponent is 0x000 - 1023: +/-0 or subnormal.
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// - Exponent is 0x7ff - 1023: +/-INFINITY or NaN
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// - This case is implicitly handled by the standard code path anyway,
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// as shifting the mantissa up by the exponent will result in '0'.
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//
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// The result is composed of the mantissa, prepended with '1' and
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// bit-shifted left by the (decoded) exponent. Note that because the r1[20]
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// is the bit with value '1', r1 is effectively already shifted (left) by
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// 20 bits, and r0 is already shifted by 52 bits.
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// Adjust the exponent to remove the encoding offset. If the decoded
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// exponent is negative, quickly bail out with '0' as such values round to
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// zero anyway. This also catches +/-0 and subnormals.
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" sub %1, %1, #0xff\n"
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" subs %1, %1, #0x300\n"
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" bmi 8f\n"
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// %1 = (decoded) exponent >= 0
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// %R4 = upper mantissa and sign
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// ---- Lower Mantissa ----
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" subs %3, %1, #52\n" // Calculate exp-52
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" bmi 1f\n"
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// Shift r0 left by exp-52.
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// Ensure that we don't overflow ARM's 8-bit shift operand range.
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// We need to handle anything up to an 11-bit value here as we know that
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// 52 <= exp <= 1024 (0x400). Any shift beyond 31 bits results in zero
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// anyway, so as long as we don't touch the bottom 5 bits, we can use
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// a logical OR to push long shifts into the 32 <= (exp&0xff) <= 255 range.
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" bic %2, %3, #0xff\n"
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" orr %3, %3, %2, LSR #3\n"
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// We can now perform a straight shift, avoiding the need for any
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// conditional instructions or extra branches.
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" mov %Q4, %Q4, LSL %3\n"
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" b 2f\n"
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"1:\n" // Shift r0 right by 52-exp.
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// We know that 0 <= exp < 52, and we can shift up to 255 bits so 52-exp
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// will always be a valid shift and we can sk%3 the range check for this case.
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" rsb %3, %1, #52\n"
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" mov %Q4, %Q4, LSR %3\n"
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// %1 = (decoded) exponent
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// %R4 = upper mantissa and sign
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// %Q4 = partially-converted integer
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"2:\n"
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// ---- Upper Mantissa ----
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// This is much the same as the lower mantissa, with a few different
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// boundary checks and some masking to hide the exponent & sign bit in the
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// upper word.
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// Note that the upper mantissa is pre-shifted by 20 in %R4, but we shift
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// it left more to remove the sign and exponent so it is effectively
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// pre-shifted by 31 bits.
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" subs %3, %1, #31\n" // Calculate exp-31
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" mov %1, %R4, LSL #11\n" // Re-use %1 as a temporary register.
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" bmi 3f\n"
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// Shift %R4 left by exp-31.
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// Avoid overflowing the 8-bit shift range, as before.
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" bic %2, %3, #0xff\n"
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" orr %3, %3, %2, LSR #3\n"
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// Perform the shift.
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" mov %2, %1, LSL %3\n"
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" b 4f\n"
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"3:\n" // Shift r1 right by 31-exp.
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// We know that 0 <= exp < 31, and we can shift up to 255 bits so 31-exp
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// will always be a valid shift and we can skip the range check for this case.
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" rsb %3, %3, #0\n" // Calculate 31-exp from -(exp-31)
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" mov %2, %1, LSR %3\n" // Thumb-2 can't do "LSR %3" in "orr".
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// %Q4 = partially-converted integer (lower)
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// %R4 = upper mantissa and sign
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// %2 = partially-converted integer (upper)
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"4:\n"
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// Combine the converted parts.
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" orr %Q4, %Q4, %2\n"
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// Negate the result if we have to, and move it to %0 in the process. To
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// avoid conditionals, we can do this by inverting on %R4[31], then adding
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// %R4[31]>>31.
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" eor %Q4, %Q4, %R4, ASR #31\n"
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" add %0, %Q4, %R4, LSR #31\n"
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" b 9f\n"
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"8:\n"
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// +/-INFINITY, +/-0, subnormals, NaNs, and anything else out-of-range that
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// will result in a conversion of '0'.
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" mov %0, #0\n"
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"9:\n"
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: "=r" (i), "=&r" (tmp0), "=&r" (tmp1), "=&r" (tmp2), "=&r" (d)
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: "4" (d)
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: "cc"
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);
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return i;
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|
#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 4.2.10 */
|
|
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 */
|