small optimization in Field_time_hires.

Fix Field_time_hires::reset()

sql/field.cc

@@ -5364,11 +5364,15 @@ void Field_time::sql_type(String &res) const
   res.set_ascii(STRING_WITH_LEN("time"));
 }
 
-static const longlong t_shift= ((TIME_MAX_VALUE_SECONDS+1)*TIME_SECOND_PART_FACTOR);
+int Field_time_hires::reset()
+{
+  store_bigendian(zero_point, ptr, Field_time_hires::pack_length());
+  return 0;
+}
+
 void Field_time_hires::store_TIME(MYSQL_TIME *ltime)
 {
-  ulonglong packed= sec_part_shift(pack_time(ltime), dec) +
-                    sec_part_shift(t_shift, dec);
+  ulonglong packed= sec_part_shift(pack_time(ltime), dec) + zero_point;
   store_bigendian(packed, ptr, Field_time_hires::pack_length());
 }
 
@@ -5425,8 +5429,7 @@ bool Field_time_hires::get_date(MYSQL_TIME *ltime, uint fuzzydate)
   uint32 len= pack_length();
   longlong packed= read_bigendian(ptr, len);
 
-  if (packed)
-    packed= sec_part_unshift(packed - sec_part_shift(t_shift, dec), dec);
+  packed= sec_part_unshift(packed - zero_point, dec);
 
   unpack_time(packed, ltime);
   /*

sql/field.h

@@ -1420,6 +1420,7 @@ class Field_time :public Field_temporal {
 
 class Field_time_hires :public Field_time {
   uint dec;
+  longlong zero_point;
   void store_TIME(MYSQL_TIME *ltime);
 public:
   Field_time_hires(uchar *ptr_arg, uchar *null_ptr_arg, uchar null_bit_arg,
@@ -1431,6 +1432,8 @@ class Field_time_hires :public Field_time {
   {
     DBUG_ASSERT(dec);
     DBUG_ASSERT(dec <= TIME_SECOND_PART_DIGITS);
+    zero_point= sec_part_shift(
+                   ((TIME_MAX_VALUE_SECONDS+1)*TIME_SECOND_PART_FACTOR), dec);
   }
   enum ha_base_keytype key_type() const { return HA_KEYTYPE_BINARY; }
   uint decimals() const { return dec; }
@@ -1438,6 +1441,7 @@ class Field_time_hires :public Field_time {
   longlong val_int(void);
   double val_real(void);
   String *val_str(String*,String *);
+  int reset(void);
   bool get_date(MYSQL_TIME *ltime, uint fuzzydate);
   bool send_binary(Protocol *protocol);
   int cmp(const uchar *,const uchar *);