1 files changed, 170 insertions, 0 deletions
diff --git a/js/public/Date.h b/js/public/Date.h
new file mode 100644
index 000000000..cba0ea875
--- /dev/null
+++ b/js/public/Date.h
@@ -0,0 +1,170 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+/* JavaScript date/time computation and creation functions. */
+
+#ifndef js_Date_h
+#define js_Date_h
+
+/*
+ * Dates in JavaScript are defined by IEEE-754 double precision numbers from
+ * the set:
+ *
+ *   { t ∈ ℕ : -8.64e15 ≤ t ≤ +8.64e15 } ∪ { NaN }
+ *
+ * The single NaN value represents any invalid-date value.  All other values
+ * represent idealized durations in milliseconds since the UTC epoch.  (Leap
+ * seconds are ignored; leap days are not.)  +0 is the only zero in this set.
+ * The limit represented by 8.64e15 milliseconds is 100 million days either
+ * side of 00:00 January 1, 1970 UTC.
+ *
+ * Dates in the above set are represented by the |ClippedTime| class.  The
+ * double type is a superset of the above set, so it *may* (but need not)
+ * represent a date.  Use ECMAScript's |TimeClip| method to produce a date from
+ * a double.
+ *
+ * Date *objects* are simply wrappers around |TimeClip|'d numbers, with a bunch
+ * of accessor methods to the various aspects of the represented date.
+ */
+
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/MathAlgorithms.h"
+
+#include "js/Conversions.h"
+#include "js/Value.h"
+
+struct JSContext;
+
+namespace JS {
+
+/**
+ * Re-query the system to determine the current time zone adjustment from UTC,
+ * including any component due to DST.  If the time zone has changed, this will
+ * cause all Date object non-UTC methods and formatting functions to produce
+ * appropriately adjusted results.
+ *
+ * Left to its own devices, SpiderMonkey itself may occasionally call this
+ * method to attempt to keep up with system time changes.  However, no
+ * particular frequency of checking is guaranteed.  Embedders unable to accept
+ * occasional inaccuracies should call this method in response to system time
+ * changes, or immediately before operations requiring instantaneous
+ * correctness, to guarantee correct behavior.
+ */
+extern JS_PUBLIC_API(void)
+ResetTimeZone();
+
+class ClippedTime;
+inline ClippedTime TimeClip(double time);
+
+/*
+ * |ClippedTime| represents the limited subset of dates/times described above.
+ *
+ * An invalid date/time may be created through the |ClippedTime::invalid|
+ * method.  Otherwise, a |ClippedTime| may be created using the |TimeClip|
+ * method.
+ *
+ * In typical use, the user might wish to manipulate a timestamp.  The user
+ * performs a series of operations on it, but the final value might not be a
+ * date as defined above -- it could have overflowed, acquired a fractional
+ * component, &c.  So as a *final* step, the user passes that value through
+ * |TimeClip| to produce a number restricted to JavaScript's date range.
+ *
+ * APIs that accept a JavaScript date value thus accept a |ClippedTime|, not a
+ * double.  This ensures that date/time APIs will only ever receive acceptable
+ * JavaScript dates.  This also forces users to perform any desired clipping,
+ * as only the user knows what behavior is desired when clipping occurs.
+ */
+class ClippedTime
+{
+    double t;
+
+    explicit ClippedTime(double time) : t(time) {}
+    friend ClippedTime TimeClip(double time);
+
+  public:
+    // Create an invalid date.
+    ClippedTime() : t(mozilla::UnspecifiedNaN<double>()) {}
+
+    // Create an invalid date/time, more explicitly; prefer this to the default
+    // constructor.
+    static ClippedTime invalid() { return ClippedTime(); }
+
+    double toDouble() const { return t; }
+
+    bool isValid() const { return !mozilla::IsNaN(t); }
+};
+
+// ES6 20.3.1.15.
+//
+// Clip a double to JavaScript's date range (or to an invalid date) using the
+// ECMAScript TimeClip algorithm.
+inline ClippedTime
+TimeClip(double time)
+{
+    // Steps 1-2.
+    const double MaxTimeMagnitude = 8.64e15;
+    if (!mozilla::IsFinite(time) || mozilla::Abs(time) > MaxTimeMagnitude)
+        return ClippedTime(mozilla::UnspecifiedNaN<double>());
+
+    // Step 3.
+    return ClippedTime(ToInteger(time) + (+0.0));
+}
+
+// Produce a double Value from the given time.  Because times may be NaN,
+// prefer using this to manual canonicalization.
+inline Value
+TimeValue(ClippedTime time)
+{
+    return DoubleValue(JS::CanonicalizeNaN(time.toDouble()));
+}
+
+// Create a new Date object whose [[DateValue]] internal slot contains the
+// clipped |time|.  (Users who must represent times outside that range must use
+// another representation.)
+extern JS_PUBLIC_API(JSObject*)
+NewDateObject(JSContext* cx, ClippedTime time);
+
+// Year is a year, month is 0-11, day is 1-based.  The return value is a number
+// of milliseconds since the epoch.
+//
+// Consistent with the MakeDate algorithm defined in ECMAScript, this value is
+// *not* clipped!  Use JS::TimeClip if you need a clipped date.
+JS_PUBLIC_API(double)
+MakeDate(double year, unsigned month, unsigned day);
+
+// Takes an integer number of milliseconds since the epoch and returns the
+// year.  Can return NaN, and will do so if NaN is passed in.
+JS_PUBLIC_API(double)
+YearFromTime(double time);
+
+// Takes an integer number of milliseconds since the epoch and returns the
+// month (0-11).  Can return NaN, and will do so if NaN is passed in.
+JS_PUBLIC_API(double)
+MonthFromTime(double time);
+
+// Takes an integer number of milliseconds since the epoch and returns the
+// day (1-based).  Can return NaN, and will do so if NaN is passed in.
+JS_PUBLIC_API(double)
+DayFromTime(double time);
+
+// Takes an integer year and returns the number of days from epoch to the given
+// year.
+// NOTE: The calculation performed by this function is literally that given in
+// the ECMAScript specification.  Nonfinite years, years containing fractional
+// components, and years outside ECMAScript's date range are not handled with
+// any particular intelligence.  Garbage in, garbage out.
+JS_PUBLIC_API(double)
+DayFromYear(double year);
+
+// Takes an integer number of milliseconds since the epoch and an integer year,
+// returns the number of days in that year. If |time| is nonfinite, returns NaN.
+// Otherwise |time| *must* correspond to a time within the valid year |year|.
+// This should usually be ensured by computing |year| as |JS::DayFromYear(time)|.
+JS_PUBLIC_API(double)
+DayWithinYear(double time, double year);
+
+} // namespace JS
+
+#endif /* js_Date_h */