Bug#41470: DATE_FORMAT() crashes the complete server with a valid date

Passing dubious "year zero" in non-zero date (not "0000-00-00") could
lead to negative value for year internally, while variable was unsigned.
This led to Really Bad Things further down the line.

Now doing calculations with signed type for year internally.

mysql-test/r/date_formats.result

@@ -593,3 +593,13 @@ select str_to_date('04/30/2004 ', '%m/%d/%Y ');
 str_to_date('04/30/2004 ', '%m/%d/%Y ')
 2004-04-30
 "End of 4.1 tests"
+SELECT DATE_FORMAT("0000-01-01",'%W %d %M %Y') as valid_date;
+valid_date
+Sunday 01 January 0000
+SELECT DATE_FORMAT("0000-02-28",'%W %d %M %Y') as valid_date;
+valid_date
+Tuesday 28 February 0000
+SELECT DATE_FORMAT("2009-01-01",'%W %d %M %Y') as valid_date;
+valid_date
+Thursday 01 January 2009
+"End of 5.0 tests"

mysql-test/t/date_formats.test

@@ -337,3 +337,15 @@ select str_to_date('04/30 /2004', '%m /%d /%Y');
 select str_to_date('04/30/2004 ', '%m/%d/%Y ');
 
 --echo "End of 4.1 tests"
+
+#
+# Bug #41470: DATE_FORMAT() crashes the complete server with a valid date
+#
+
+# show that these two do not crash the server:
+SELECT DATE_FORMAT("0000-01-01",'%W %d %M %Y') as valid_date;
+SELECT DATE_FORMAT("0000-02-28",'%W %d %M %Y') as valid_date;
+# show that date within the Gregorian range render correct results: (THU)
+SELECT DATE_FORMAT("2009-01-01",'%W %d %M %Y') as valid_date;
+
+--echo "End of 5.0 tests"

sql-common/my_time.c

@@ -765,19 +765,20 @@ long calc_daynr(uint year,uint month,uint day)
 {
   long delsum;
   int temp;
+  int y= year;                                  /* may be < 0 temporarily */
   DBUG_ENTER("calc_daynr");
 
-  if (year == 0 && month == 0 && day == 0)
+  if (y == 0 && month == 0 && day == 0)
     DBUG_RETURN(0);				/* Skip errors */
-  delsum= (long) (365L * year+ 31*(month-1) +day);
+  delsum= (long) (365L * y+ 31*(month-1) +day);
   if (month <= 2)
-      year--;
+      y--;
   else
     delsum-= (long) (month*4+23)/10;
-  temp=(int) ((year/100+1)*3)/4;
+  temp=(int) ((y/100+1)*3)/4;
   DBUG_PRINT("exit",("year: %d  month: %d  day: %d -> daynr: %ld",
-		     year+(month <= 2),month,day,delsum+year/4-temp));
-  DBUG_RETURN(delsum+(int) year/4-temp);
+		     y+(month <= 2),month,day,delsum+y/4-temp));
+  DBUG_RETURN(delsum+(int) y/4-temp);
 } /* calc_daynr */