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139 lines
4.7 KiB
C++
139 lines
4.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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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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/* JavaScript date/time computation and creation functions. */
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#ifndef js_Date_h
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#define js_Date_h
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/*
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* Dates in JavaScript are defined by IEEE-754 double precision numbers from
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* the set:
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*
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* { t ∈ ℕ : -8.64e15 ≤ t ≤ +8.64e15 } ∪ { NaN }
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*
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* The single NaN value represents any invalid-date value. All other values
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* represent idealized durations in milliseconds since the UTC epoch. (Leap
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* seconds are ignored; leap days are not.) +0 is the only zero in this set.
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* The limit represented by 8.64e15 milliseconds is 100 million days either
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* side of 00:00 January 1, 1970 UTC.
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*
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* Dates in the above set are represented by the |ClippedTime| class. The
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* double type is a superset of the above set, so it *may* (but need not)
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* represent a date. Use ECMAScript's |TimeClip| method to produce a date from
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* a double.
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*
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* Date *objects* are simply wrappers around |TimeClip|'d numbers, with a bunch
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* of accessor methods to the various aspects of the represented date.
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*/
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#include "mozilla/FloatingPoint.h"
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#include "mozilla/MathAlgorithms.h"
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#include "js/Conversions.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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class ClippedTime;
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inline ClippedTime TimeClip(double time);
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/*
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* |ClippedTime| represents the limited subset of dates/times described above.
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*
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* An invalid date/time may be created through the |ClippedTime::invalid|
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* method. Otherwise, a |ClippedTime| may be created using the |TimeClip|
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* method.
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*
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* In typical use, the user might wish to manipulate a timestamp. The user
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* performs a series of operations on it, but the final value might not be a
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* date as defined above -- it could have overflowed, acquired a fractional
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* component, &c. So as a *final* step, the user passes that value through
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* |TimeClip| to produce a number restricted to JavaScript's date range.
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*
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* APIs that accept a JavaScript date value thus accept a |ClippedTime|, not a
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* double. This ensures that date/time APIs will only ever receive acceptable
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* JavaScript dates. This also forces users to perform any desired clipping,
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* as only the user knows what behavior is desired when clipping occurs.
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*/
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class ClippedTime
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{
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double t;
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explicit ClippedTime(double time) : t(time) {}
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friend ClippedTime TimeClip(double time);
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public:
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// Create an invalid date.
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ClippedTime() : t(mozilla::UnspecifiedNaN<double>()) {}
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// Create an invalid date/time, more explicitly; prefer this to the default
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// constructor.
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static ClippedTime invalid() { return ClippedTime(); }
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double toDouble() const { return t; }
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bool isValid() const { return !mozilla::IsNaN(t); }
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};
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// ES6 20.3.1.15.
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//
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// Clip a double to JavaScript's date range (or to an invalid date) using the
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// ECMAScript TimeClip algorithm.
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inline ClippedTime
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TimeClip(double time)
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{
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// Steps 1-2.
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const double MaxTimeMagnitude = 8.64e15;
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if (!mozilla::IsFinite(time) || mozilla::Abs(time) > MaxTimeMagnitude)
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return ClippedTime(mozilla::UnspecifiedNaN<double>());
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// Step 3.
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return ClippedTime(ToInteger(time) + (+0.0));
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}
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// Produce a double Value from the given time. Because times may be NaN,
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// prefer using this to manual canonicalization.
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inline Value
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TimeValue(ClippedTime time)
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{
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return DoubleValue(JS::CanonicalizeNaN(time.toDouble()));
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}
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// Create a new Date object whose [[DateValue]] internal slot contains the
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// clipped |time|. (Users who must represent times outside that range must use
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// another representation.)
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extern JS_PUBLIC_API(JSObject*)
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NewDateObject(JSContext* cx, ClippedTime time);
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// Year is a year, month is 0-11, day is 1-based. The return value is a number
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// of milliseconds since the epoch.
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//
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// Consistent with the MakeDate algorithm defined in ECMAScript, this value is
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// *not* clipped! Use JS::TimeClip if you need a clipped date.
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JS_PUBLIC_API(double)
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MakeDate(double year, unsigned month, unsigned day);
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// Takes an integer number of milliseconds since the epoch and returns the
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// year. Can return NaN, and will do so if NaN is passed in.
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JS_PUBLIC_API(double)
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YearFromTime(double time);
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// Takes an integer number of milliseconds since the epoch and returns the
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// month (0-11). Can return NaN, and will do so if NaN is passed in.
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JS_PUBLIC_API(double)
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MonthFromTime(double time);
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// Takes an integer number of milliseconds since the epoch and returns the
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// day (1-based). Can return NaN, and will do so if NaN is passed in.
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JS_PUBLIC_API(double)
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DayFromTime(double time);
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} // namespace JS
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#endif /* js_Date_h */
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