Function getDayFraction

src/dsql/ExprNodes.cpp:13951–13991

Take the input number, assume it represents a fractional count of days. Convert it to a count of microseconds.

// Take the input number, assume it represents a fractional count of days.
// Convert it to a count of microseconds.
static SINT64 getDayFraction(const dsc* d)
{
	dsc result;
	double result_days;
	thread_db* tdbb = JRD_get_thread_data();

	result.dsc_dtype = dtype_double;
	result.dsc_scale = 0;
	result.dsc_flags = 0;
	result.dsc_sub_type = 0;
	result.dsc_length = sizeof(double);
	result.dsc_address = reinterpret_cast<UCHAR*>(&result_days);

	// Convert the input number to a double
	CVT_move(d, &result, tdbb->getAttachment()->att_dec_status);

	if (fb_utils::abs64Compare(result_days, TimeStamp::MAX_DATE - TimeStamp::MIN_DATE) > 0)
		ERR_post(Arg::Gds(isc_date_range_exceeded));

	// There's likely some loss of precision here due to rounding of number

	// 08-Apr-2004, Nickolay Samofatov. Loss of precision manifested itself as bad
	// result returned by the following query:
	//
	// select (cast('01.01.2004 10:01:00' as timestamp)
	//   -cast('01.01.2004 10:00:00' as timestamp))
	//   +cast('01.01.2004 10:00:00' as timestamp) from rdb$database
	//
	// Let's use llrint where it is supported and offset number for other platforms
	// in hope that compiler rounding mode doesn't get in.

#ifdef HAVE_LLRINT
	return llrint(result_days * TimeStamp::ISC_TICKS_PER_DAY);
#else
	const double eps = 0.49999999999999;
	if (result_days >= 0)
		return (SINT64)(result_days * TimeStamp::ISC_TICKS_PER_DAY + eps);

	return (SINT64) (result_days * TimeStamp::ISC_TICKS_PER_DAY - eps);
#endif
}

// Take the input value, which is either a timestamp or a string representing a timestamp.
// Convert it to a timestamp, and then return that timestamp as a count of isc_ticks since the base