Rewrite MakeDay function from JS to C++.

src/date-delay.js

Index: src/date-delay.js
===================================================================
--- src/date-delay.js	(revision 3986)
+++ src/date-delay.js	(working copy)
@@ -113,8 +113,12 @@
   // we must do this, but for compatibility with other browsers, we use
   // the actual year if it is in the range 1970..2037
   if (t >= 0 && t <= 2.1e12) return t;
-  var day = MakeDay(EquivalentYear(YEAR_FROM_TIME(t)), MONTH_FROM_TIME(t), DATE_FROM_TIME(t));
-  return TimeClip(MakeDate(day, TimeWithinDay(t)));
+
+  // We call function from runtime.cc to avoid extra checks which are unneeded.
+  var day = %DateMakeDay(EquivalentYear(YEAR_FROM_TIME(t)),
+                         MONTH_FROM_TIME(t),
+                         DATE_FROM_TIME(t));
+  return MakeDate(day, TimeWithinDay(t));
 }
 
 
@@ -257,14 +261,6 @@
 }
 
 
-// Compute modified Julian day from year, month, date.
-function ToJulianDay(year, month, date) {
-  var jy = (month > 1) ? year : year - 1;
-  var jm = (month > 1) ? month + 2 : month + 14;
-  var ja = FLOOR(jy / 100);
-  return FLOOR(FLOOR(365.25*jy) + FLOOR(30.6001*jm) + date + 1720995) + 2 - ja + FLOOR(0.25*ja);
-}
-
 var four_year_cycle_table = CalculateDateTable();
 
 
@@ -359,20 +355,18 @@
 function MakeDay(year, month, date) {
   if (!$isFinite(year) || !$isFinite(month) || !$isFinite(date)) return $NaN;
 
-  // Conversion to integers.
   year = TO_INTEGER(year);
   month = TO_INTEGER(month);
   date = TO_INTEGER(date);
 
-  // Overflow months into year.
-  year = year + FLOOR(month/12);
-  month = month % 12;
-  if (month < 0) {
-    month += 12;
+  if (year < kMinYear || year > kMaxYear ||
+      month < kMinMonth || month > kMaxMonth ||
+      date < kMinDate || date > kMaxDate) {
+    return $NaN;
   }
 
-  // Return days relative to Jan 1 1970.
-  return ToJulianDay(year, month, date) - kDayZeroInJulianDay;
+  // Now we presume that year, month and date are actually SMIs.

[Mads Ager (chromium), 2010/03/02 13:04:08]

Since the runtime function probably relies on year, month and date being Smis,
we have to be 100% sure that they are.  Could you update the comment explaining
why they have to be Smis?

[Oleg Eterevsky, 2010/03/02 13:28:23]

Done.

+  return %DateMakeDay(year, month, date);
 }