From 52bc20ace2c57b106c70a6de6d7f71a54667ee54 Mon Sep 17 00:00:00 2001
From: Eric Scharff <scharff@sharedmind.(none)>
Date: Mon, 22 Oct 2007 15:53:46 -0600
Subject: [PATCH] Optimized calendar implementation.  Year can now be computed
 with arithmetic, not a loop to find the current year.

---
 classpath/java/util/Calendar.java | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/classpath/java/util/Calendar.java b/classpath/java/util/Calendar.java
index c479cc49fc..dbf16b3cc4 100644
--- a/classpath/java/util/Calendar.java
+++ b/classpath/java/util/Calendar.java
@@ -65,6 +65,9 @@ public abstract class Calendar {
     private static final int MILLIS_PER_SECOND = 1000;
 
     private static final int EPOCH_YEAR = 1970;
+    private static final int EPOCH_LEAP_YEAR = 1968;
+    private static final int DAYS_TO_EPOCH = 731;
+
     private static final int[][] DAYS_IN_MONTH = new int[][] {
       { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
       { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
@@ -85,22 +88,22 @@ public abstract class Calendar {
       return (year%4 == 0) && (year%100 != 0) || (year%400 == 0);
     }
     
-    private static int daysInYear(int year) {
-      return isLeapYear(year) ? 366 : 365;
-    }
-    
     private void parseIntoFields(long timeInMillis) {
       long days = timeInMillis / MILLIS_PER_DAY;
-      int year = EPOCH_YEAR;
-      while (days >= daysInYear(year)) {
-        days -= daysInYear(year++);
-      }
+      /* convert days since Jan 1, 1970 to days since Jan 1, 1968 */
+      days += DAYS_TO_EPOCH;
+      long years = 4 * days / 1461; /* days/365.25 = 4*days/(4*365.25) */
+      int year = (int)(EPOCH_LEAP_YEAR + years);
+      days -= 365 * years + years / 4;
+      if (!isLeapYear(year)) days--;
+      
       int month=0;
       int leapIndex = isLeapYear(year) ? 1 : 0;
       while (days >= DAYS_IN_MONTH[leapIndex][month]) {
         days -= DAYS_IN_MONTH[leapIndex][month++];
       }
       days++;
+
       int remainder = (int)(timeInMillis % MILLIS_PER_DAY);
       int hour = remainder / MILLIS_PER_HOUR;
       remainder = remainder % MILLIS_PER_HOUR;