1 files changed, 209 insertions, 0 deletions
diff --git a/js/public/Date.h b/js/public/Date.h
new file mode 100644
index 0000000000..e7a54d86c4
--- /dev/null
+++ b/js/public/Date.h
@@ -0,0 +1,209 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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"  // mozilla::{IsFinite,IsNaN}, mozilla::UnspecifiedNaN
+#include "mozilla/MathAlgorithms.h"  // mozilla::Abs
+
+#include "js/Conversions.h"  // JS::ToInteger
+#include "js/RootingAPI.h"   // JS::Handle
+#include "js/Value.h"        // JS::CanonicalizeNaN, JS::DoubleValue, JS::Value
+
+struct JS_PUBLIC_API JSContext;
+class JS_PUBLIC_API JSObject;
+
+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 try to detect
+ * 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 = mozilla::UnspecifiedNaN<double>();
+
+  explicit ClippedTime(double time) : t(time) {}
+  friend ClippedTime TimeClip(double time);
+
+ public:
+  // Create an invalid date.
+  ClippedTime() = default;
+
+  // 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));
+}
+
+// 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 CanonicalizedDoubleValue(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);
+
+/**
+ * Create a new Date object for a year/month/day-of-month/hour/minute/second.
+ *
+ * The created date is initialized with the time value
+ *
+ *   TimeClip(UTC(MakeDate(MakeDay(year, mon, mday),
+ *                MakeTime(hour, min, sec, 0.0))))
+ *
+ * where each function/operation is as specified in ECMAScript.
+ */
+extern JS_PUBLIC_API JSObject* NewDateObject(JSContext* cx, int year, int mon,
+                                             int mday, int hour, int min,
+                                             int sec);
+
+/**
+ * On success, returns true, setting |*isDate| to true if |obj| is a Date
+ * object or a wrapper around one, or to false if not.  Returns false on
+ * failure.
+ *
+ * This method returns true with |*isDate == false| when passed an ES6 proxy
+ * whose target is a Date, or when passed a revoked proxy.
+ */
+extern JS_PUBLIC_API bool ObjectIsDate(JSContext* cx, Handle<JSObject*> obj,
+                                       bool* isDate);
+
+// 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);
+
+// Year is a year, month is 0-11, day is 1-based, and time is in milliseconds.
+// 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,
+                              double time);
+
+// 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);
+
+// The callback will be a wrapper function that accepts a single double (the
+// time to clamp and jitter.) Inside the JS Engine, other parameters that may be
+// needed are all constant, so they are handled inside the wrapper function
+using ReduceMicrosecondTimePrecisionCallback = double (*)(double, JSContext*);
+
+// Set a callback into the toolkit/components/resistfingerprinting function that
+// will centralize time resolution and jitter into one place.
+JS_PUBLIC_API void SetReduceMicrosecondTimePrecisionCallback(
+    ReduceMicrosecondTimePrecisionCallback callback);
+
+// Sets the time resolution for fingerprinting protection, and whether jitter
+// should occur. If resolution is set to zero, then no rounding or jitter will
+// occur. This is used if the callback above is not specified.
+JS_PUBLIC_API void SetTimeResolutionUsec(uint32_t resolution, bool jitter);
+
+}  // namespace JS
+
+#endif /* js_Date_h */