fix(WDate): handle negative (BCE) years correctly#252
Open
saddamr3e wants to merge 2 commits into
Open
Conversation
WDate::setYmd packed the year into an unsigned int field using a left-shift on a signed int (y << 16). When the year is negative (BCE dates), this is undefined behavior in C++11/14/17. Even where the platform produces a deterministic result, the unsigned storage caused operator<() to return wrong results (a BCE date compared greater than any CE date) and year() to return a garbage positive value (e.g., 65535 for year -1). The API explicitly supports negative years: fromJulianDay() produces years as far back as -4713 (Julian Day epoch), and setDate() accepts any year in [date::year::min(), date::year::max()] = [-32768, 32767]. Fix: - Change ymd_ from unsigned to int so that operator<() performs a signed comparison (correct for BCE vs CE ordering) and year() returns the right value via arithmetic right-shift. - In setYmd(), cast y to unsigned before shifting (shifting unsigned is always well-defined in C++) then static_cast<int> the result back into ymd_, preserving the two's-complement bit pattern. - Fix isValid() from (ymd_ > 1) to (ymd_ != 0 && ymd_ != 1). The old guard relied on valid dates always being > 1, which holds for CE years but fails for BCE years whose packed ymd_ is negative. All downstream methods (dayOfWeek, daysTo, toJulianDay, toTimePoint, addDays, addMonths, addYears, toString, fromJulianDay, previousWeekday) are fixed transitively since they all call year().
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
While testing WDate with negative (BCE) years, I noticed that dates before the common era do not behave correctly.
The date is packed internally in WDate::setYmd() by shifting the year value and storing the result in an unsigned field. For negative years, this leads to incorrect behavior, causing BCE dates to compare incorrectly and making year values inconsistent.
This change preserves negative years correctly when packing the date and stores the packed value in a signed field. It also updates the validity check so BCE dates are handled consistently.
I also added a regression test to cover BCE dates and ensure comparisons and year extraction continue to work correctly.