数据库内核月报 － 2022 / 12

CREATE TABLE t1 (t TIME(3), dt DATETIME(6), ts TIMESTAMP(0));

/*
  Structure which is used to represent datetime values inside MySQL.

  We assume that values in this structure are normalized, i.e. year <= 9999,
  month <= 12, day <= 31, hour <= 23, second <= 59. Many functions
  in server such as my_system_gmt_sec() or make_time() family of functions
  rely on this (actually now usage of make_*() family relies on a bit weaker
  restriction). Also functions that produce MYSQL_TIME as result ensure this.
  There is one exception to this rule though if this structure holds time
  value (time_type == MYSQL_TIMESTAMP_TIME) days and hour member can hold
  bigger values.
*/
typedef struct MYSQL_TIME {
  unsigned int year, month, day, hour, minute, second;
  unsigned long second_part; /**< microseconds */
  bool neg;
  enum enum_mysql_timestamp_type time_type;
} MYSQL_TIME;

typedef struct timeval {
  long tv_sec;
  long tv_usec;
} timeval;

/**
  Convert in-memory date representation to on-disk representation.

  @param        ltime The value to convert.
  @param [out]  ptr   The pointer to store the value to.
*/
void my_date_to_binary(const MYSQL_TIME *ltime, uchar *ptr) {
  long tmp = ltime->day + ltime->month * 32 + ltime->year * 16 * 32;
  int3store(ptr, tmp);
}

/**
  Convert time value to numeric packed representation.

  @param    my_time The value to convert.
  @return           Numeric packed representation.
*/
longlong TIME_to_longlong_time_packed(const MYSQL_TIME &my_time) {
  /* If month is 0, we mix day with hours: "1 00:10:10" -> "24:00:10" */
  long hms = (((my_time.month ? 0 : my_time.day * 24) + my_time.hour) << 12) |
             (my_time.minute << 6) | my_time.second;
  longlong tmp = my_packed_time_make(hms, my_time.second_part);
  return my_time.neg ? -tmp : tmp;
}

/**
  Convert datetime to packed numeric datetime representation.

  @param my_time  The value to convert.
  @return       Packed numeric representation of my_time.
*/
longlong TIME_to_longlong_datetime_packed(const MYSQL_TIME &my_time) {
  longlong ymd = ((my_time.year * 13 + my_time.month) << 5) | my_time.day;
  longlong hms = (my_time.hour << 12) | (my_time.minute << 6) | my_time.second;
  longlong tmp = my_packed_time_make(((ymd << 17) | hms), my_time.second_part);
  assert(!check_datetime_range(my_time)); /* Make sure no overflow */
  return my_time.neg ? -tmp : tmp;
}

/**
  On disk we convert from signed representation to unsigned
  representation using TIMEF_OFS, so all values become binary comparable.
*/
#define TIMEF_OFS 0x800000000000LL
#define TIMEF_INT_OFS 0x800000LL

/**
  Convert in-memory numeric time representation to on-disk representation

  @param       nr   Value in packed numeric time format.
  @param [out] ptr  The buffer to put value at.
  @param       dec  Precision.
*/
void my_time_packed_to_binary(longlong nr, uchar *ptr, uint dec) {
  assert(dec <= DATETIME_MAX_DECIMALS);
  /* Make sure the stored value was previously properly rounded or truncated */
  assert((my_packed_time_get_frac_part(nr) %
          static_cast<int>(log_10_int[DATETIME_MAX_DECIMALS - dec])) == 0);

  switch (dec) {
    case 0:
    default:
      mi_int3store(ptr, TIMEF_INT_OFS + my_packed_time_get_int_part(nr));
      break;

    case 1:
    case 2:
      mi_int3store(ptr, TIMEF_INT_OFS + my_packed_time_get_int_part(nr));
      ptr[3] = static_cast<unsigned char>(
          static_cast<char>(my_packed_time_get_frac_part(nr) / 10000));
      break;

    case 4:
    case 3:
      mi_int3store(ptr, TIMEF_INT_OFS + my_packed_time_get_int_part(nr));
      mi_int2store(ptr + 3, my_packed_time_get_frac_part(nr) / 100);
      break;

    case 5:
    case 6:
      mi_int6store(ptr, nr + TIMEF_OFS);
      break;
  }
}