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WeekSpan

Function WeekSpan( const ANow, AThen : TDateTime) : Double

Example​

procedure ScriptEvent(var Value: variant);
var
  FirstValue, SecondValue: TDateTime;
begin
  FirstValue := EncodeDateTime(2026, 1, 1, 0, 0, 0, 0);
  SecondValue := EncodeDateTime(2026, 1, 11, 12, 0, 0, 0);
  Value := WeekSpan(FirstValue, SecondValue);
  // Value is 1.5.
end;

Usage​

WeekSpan returns an absolute fractional-week span from Velox's raw numeric TDateTime difference.

Parameters

NameTypeDescription
ANowTDateTimeOne encoded endpoint. It need not be later than AThen.
AThenTDateTimeThe other encoded endpoint.

Returns

A non-negative Double: the raw absolute day difference divided by 7.

Behaviour

For ordinary non-negative TDateTime values, the integer portion is days since the Velox epoch and the fractional portion is time of day, so raw subtraction provides the expected fractional duration. Reversing the parameters leaves the result unchanged.

Errors

The binding performs no range or finite-value validation. Floating-point or conversion errors from invalid inputs are not caught by Velox.

Additional Technical Info​

Returns an absolute, fractional number of seven-day periods between ANow and AThen. Unlike WeeksBetween, it preserves the fractional portion and operates directly on the floating-point representation of TDateTime.

Implementation

Velox binds directly to System.DateUtils.WeekSpan. The installed function calls DaySpan, which calls SpanOfNowAndThen. That helper compares the two raw Double values, subtracts the smaller numeric value from the larger, and then WeekSpan divides the result by DaysPerWeek (7). It does not convert either endpoint to a chronological timestamp.

Edge cases and quirks

  • Delphi represents times on dates before 30 December 1899 with a negative value whose fractional part is also negative. Raw subtraction can therefore mismeasure intervals wholly before, or crossing, that epoch. Use WeeksBetween/DaysBetween or a timestamp-normalised calculation when pre-epoch chronology matters.
  • The result is floating-point. Exact comparisons at a boundary can be affected by binary rounding; compare with an appropriate tolerance when necessary.
  • The function measures seven encoded days, not ISO week-number or calendar boundaries.
  • No timezone or daylight-saving adjustment occurs.

Performance and concurrency

The operation is constant-time floating-point arithmetic with no allocation or shared Velox state.

Related entries

  • WeeksBetween — returns complete weeks after millisecond timestamp normalisation.
  • DaySpan — supplies the raw day span used here.
  • YearSpan — applies the same raw subtraction with a 365.25-day divisor.

External references

Created 2026-07-15