Fix for bug #8068 "TIMEDIFF with first negative argument gives wrong

result" (and similar bug in ADDTIME/SUBTIME).

Both Item_func_add_time/Item_func_timediff::val_str() now use
calc_time_diff() function which was backported from 5.0 (and which
was was fixed to properly handle microseconds part of its second 
argument). Also now we correctly set sign of result in case when
first argument is negative and second is positive.  

mysql-test/r/func_sapdb.result

@@ -185,6 +185,7 @@ insert into test values
 ('2001-01-01 01:01:01', '-01:01:01', '-23:59:59', "1997-12-31 23:59:59.000001"),
 ('1997-12-31 23:59:59.000001', '-23:59:59', '-01:01:01', '2001-01-01 01:01:01'),
 ('2001-01-01 01:01:01', '01:01:01', '-1 01:01:01', null),
+('2001-01-01 01:01:01', '-01:01:01', '1 01:01:01', '2001-01-01 01:01:01'),
 ('2001-01-01 01:01:01', null, '-1 01:01:01', null),
 (null, null, null, null),
 ('2001-01-01 01:01:01', '01:01:01', '1 01:01:01', '2001-01-01 01:01:01');
@@ -194,6 +195,7 @@ ttt	qqq
 2001-01-01 00:00:00	-25:01:00
 1997-12-31 00:00:00	-25:01:00
 2001-01-01 02:02:02	-24:00:00
+2001-01-01 00:00:00	24:00:00
 NULL	NULL
 NULL	NULL
 2001-01-01 02:02:02	26:02:02
@@ -203,6 +205,7 @@ ttt	qqq
 26305:01:02	22:58:58
 -26305:01:02	-22:58:58
 NULL	26:02:02
+00:00:00	-26:02:02
 NULL	NULL
 NULL	NULL
 00:00:00	-24:00:00

mysql-test/t/func_sapdb.test

@@ -100,6 +100,7 @@ insert into test values
 ('2001-01-01 01:01:01', '-01:01:01', '-23:59:59', "1997-12-31 23:59:59.000001"),
 ('1997-12-31 23:59:59.000001', '-23:59:59', '-01:01:01', '2001-01-01 01:01:01'),
 ('2001-01-01 01:01:01', '01:01:01', '-1 01:01:01', null),
+('2001-01-01 01:01:01', '-01:01:01', '1 01:01:01', '2001-01-01 01:01:01'),
 ('2001-01-01 01:01:01', null, '-1 01:01:01', null),
 (null, null, null, null),
 ('2001-01-01 01:01:01', '01:01:01', '1 01:01:01', '2001-01-01 01:01:01');

sql/item_timefunc.cc

@@ -761,6 +761,81 @@ static bool get_interval_info(const char *str,uint length,CHARSET_INFO *cs,
 }
 
 
+/*
+  Calculate difference between two datetime values as seconds + microseconds.
+
+  SYNOPSIS
+    calc_time_diff()
+      l_time1         - TIME/DATE/DATETIME value
+      l_time2         - TIME/DATE/DATETIME value
+      l_sign          - 1 absolute values are substracted,
+                        -1 absolute values are added.
+      seconds_out     - Out parameter where difference between
+                        l_time1 and l_time2 in seconds is stored.
+      microseconds_out- Out parameter where microsecond part of difference
+                        between l_time1 and l_time2 is stored.
+
+  NOTE
+    This function calculates difference between l_time1 and l_time2 absolute
+    values. So one should set l_sign and correct result if he want to take
+    signs into account (i.e. for TIME values).
+
+  RETURN VALUES
+    Returns sign of difference.
+    1 means negative result
+    0 means positive result
+
+*/
+
+static bool calc_time_diff(TIME *l_time1, TIME *l_time2, int l_sign,
+                           longlong *seconds_out, long *microseconds_out)
+{
+  long days;
+  bool neg;
+  longlong microseconds;
+
+  /*
+    We suppose that if first argument is MYSQL_TIMESTAMP_TIME
+    the second argument should be TIMESTAMP_TIME also.
+    We should check it before calc_time_diff call.
+  */
+  if (l_time1->time_type == MYSQL_TIMESTAMP_TIME)  // Time value
+    days= l_time1->day - l_sign*l_time2->day;
+  else
+  {
+    days= calc_daynr((uint) l_time1->year,
+		     (uint) l_time1->month,
+		     (uint) l_time1->day);
+    if (l_time2->time_type == MYSQL_TIMESTAMP_TIME)
+      days-= l_sign*l_time2->day;
+    else
+      days-= l_sign*calc_daynr((uint) l_time2->year,
+			       (uint) l_time2->month,
+			       (uint) l_time2->day);
+  }
+
+  microseconds= ((longlong)days*LL(86400) +
+                 (longlong)(l_time1->hour*3600L +
+                            l_time1->minute*60L +
+                            l_time1->second) -
+                 l_sign*(longlong)(l_time2->hour*3600L +
+                                   l_time2->minute*60L +
+                                   l_time2->second)) * LL(1000000) +
+                (longlong)l_time1->second_part -
+                l_sign*(longlong)l_time2->second_part;
+
+  neg= 0;
+  if (microseconds < 0)
+  {
+    microseconds= -microseconds;
+    neg= 1;
+  }
+  *seconds_out= microseconds/1000000L;
+  *microseconds_out= (long) (microseconds%1000000L);
+  return neg;
+}
+
+
 longlong Item_func_period_add::val_int()
 {
   DBUG_ASSERT(fixed == 1);
@@ -2332,11 +2407,11 @@ String *Item_func_add_time::val_str(String *str)
   DBUG_ASSERT(fixed == 1);
   TIME l_time1, l_time2, l_time3;
   bool is_time= 0;
-  long microseconds, seconds, days= 0;
+  long days, microseconds;
+  longlong seconds;
   int l_sign= sign;
 
   null_value=0;
-  l_time3.neg= 0;
   if (is_date)                        // TIMESTAMP function
   {
     if (get_arg0_date(&l_time1,1) || 
@@ -2352,51 +2427,26 @@ String *Item_func_add_time::val_str(String *str)
         l_time2.time_type == MYSQL_TIMESTAMP_DATETIME)
       goto null_date;
     is_time= (l_time1.time_type == MYSQL_TIMESTAMP_TIME);
-    if (is_time && (l_time2.neg == l_time1.neg && l_time1.neg))
-      l_time3.neg= 1;
   }
   if (l_time1.neg != l_time2.neg)
     l_sign= -l_sign;
 
-  microseconds= l_time1.second_part + l_sign*l_time2.second_part;
-  seconds= (l_time1.hour*3600L + l_time1.minute*60L + l_time1.second +
-	    (l_time2.day*86400L + l_time2.hour*3600L +
-	     l_time2.minute*60L + l_time2.second)*l_sign);
-  if (is_time)
-    seconds+= l_time1.day*86400L;
-  else
-    days+= calc_daynr((uint) l_time1.year,(uint) l_time1.month,
-		      (uint) l_time1.day);
-  seconds= seconds + microseconds/1000000L;
-  microseconds= microseconds%1000000L;
-  days+= seconds/86400L;
-  seconds= seconds%86400L;
+  l_time3.neg= calc_time_diff(&l_time1, &l_time2, -l_sign,
+			      &seconds, &microseconds);
 
-  if (microseconds < 0)
-  {
-    microseconds+= 1000000L;
-    seconds--;
-  }
-  if (seconds < 0)
-  {
-    days+= seconds/86400L - 1;
-    seconds+= 86400L;
-  }
-  if (days < 0)
-  {
-    if (!is_time)
+  /*
+    If first argument was negative and diff between arguments
+    is non-zero we need to swap sign to get proper result.
+  */
+  if (l_time1.neg && (seconds || microseconds))
+    l_time3.neg= 1-l_time3.neg;         // Swap sign of result
+
+  if (!is_time && l_time3.neg)
     goto null_date;
-    if (microseconds)
-    {
-      microseconds= 1000000L - microseconds;
-      seconds++; 
-    }
-    seconds= 86400L - seconds;
-    days= -(++days);
-    l_time3.neg= 1;
-  }
 
-  calc_time_from_sec(&l_time3, seconds, microseconds);
+  days= (long)(seconds/86400L);
+
+  calc_time_from_sec(&l_time3, (long)(seconds%86400L), microseconds);
   if (!is_time)
   {
     get_date_from_daynr(days,&l_time3.year,&l_time3.month,&l_time3.day);
@@ -2452,8 +2502,8 @@ void Item_func_add_time::print(String *str)
 String *Item_func_timediff::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
-  longlong microseconds;
-  long days;
+  longlong seconds;
+  long microseconds;
   int l_sign= 1;
   TIME l_time1 ,l_time2, l_time3;
 
@@ -2466,33 +2516,18 @@ String *Item_func_timediff::val_str(String *str)
   if (l_time1.neg != l_time2.neg)
     l_sign= -l_sign;
 
-  if (l_time1.time_type == MYSQL_TIMESTAMP_TIME) // Time value
-    days= l_time1.day - l_sign*l_time2.day;
-  else                                      // DateTime value
-    days= (calc_daynr((uint) l_time1.year,
-		      (uint) l_time1.month,
-		      (uint) l_time1.day) - 
-	   l_sign*calc_daynr((uint) l_time2.year,
-			     (uint) l_time2.month,
-			     (uint) l_time2.day));
-
-  microseconds= ((longlong)days*86400L +
-                 l_time1.hour*3600L + l_time1.minute*60L + l_time1.second -
-                 (longlong)l_sign*(l_time2.hour*3600L + l_time2.minute*60L +
-                                   l_time2.second))*1000000 +
-                 l_time1.second_part - l_sign*l_time2.second_part;
-
-  l_time3.neg= 0;
-  if (microseconds < 0)
-  {
-    microseconds= -microseconds;
-    l_time3.neg= 1;
-  }
-  if ((l_time2.neg == l_time1.neg) && l_time1.neg && microseconds)
-    l_time3.neg= l_time3.neg ? 0 : 1;
+  l_time3.neg= calc_time_diff(&l_time1, &l_time2, l_sign,
+			      &seconds, &microseconds);
+
+  /*
+    For MYSQL_TIMESTAMP_TIME only:
+      If first argument was negative and diff between arguments
+      is non-zero we need to swap sign to get proper result.
+  */
+  if (l_time1.neg && (seconds || microseconds))
+    l_time3.neg= 1-l_time3.neg;         // Swap sign of result
 
-  calc_time_from_sec(&l_time3, (long)(microseconds/1000000),
-                               (long)(microseconds%1000000));
+  calc_time_from_sec(&l_time3, (long) seconds, microseconds);
 
   if (!make_datetime(l_time1.second_part || l_time2.second_part ?
 		     TIME_MICROSECOND : TIME_ONLY,