Skip to content

Editorial: Rewrite CalendarDateUntil to be simpler and more general #3136

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 3 commits into from
Closed

Editorial: Rewrite CalendarDateUntil to be simpler and more general #3136

Changes from 1 commit
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
19e5ff9
Editorial: Rewrite CalendarDateUntil to be simpler and more general
sffc Jul 19, 2025
ff2e31a
Add exclamation marks
sffc Jul 19, 2025
9004121
Add another exclamation mark
sffc Jul 19, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
63 changes: 27 additions & 36 deletions spec/calendar.html
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -525,42 +525,33 @@ <h1>
</dd>
</dl>
<emu-alg>
1. If _calendar_ is *"iso8601"*, then
1. Let _sign_ be -CompareISODate(_one_, _two_).
1. If _sign_ = 0, return ZeroDateDuration().
1. Let _years_ be 0.
1. If _largestUnit_ is ~year~, then
1. Let _candidateYears_ be _sign_.
1. Repeat, while ISODateSurpasses(_sign_, _one_.[[Year]] + _candidateYears_, _one_.[[Month]], _one_.[[Day]], _two_) is *false*,
1. Set _years_ to _candidateYears_.
1. Set _candidateYears_ to _candidateYears_ + _sign_.
1. Let _months_ be 0.
1. If _largestUnit_ is ~year~ or _largestUnit_ is ~month~, then
1. Let _candidateMonths_ be _sign_.
1. Let _intermediate_ be BalanceISOYearMonth(_one_.[[Year]] + _years_, _one_.[[Month]] + _candidateMonths_).
1. Repeat, while ISODateSurpasses(_sign_, _intermediate_.[[Year]], _intermediate_.[[Month]], _one_.[[Day]], _two_) is *false*,
1. Set _months_ to _candidateMonths_.
1. Set _candidateMonths_ to _candidateMonths_ + _sign_.
1. Set _intermediate_ to BalanceISOYearMonth(_intermediate_.[[Year]], _intermediate_.[[Month]] + _sign_).
1. Set _intermediate_ to BalanceISOYearMonth(_one_.[[Year]] + _years_, _one_.[[Month]] + _months_).
1. Let _constrained_ be ! RegulateISODate(_intermediate_.[[Year]], _intermediate_.[[Month]], _one_.[[Day]], ~constrain~).
1. Let _weeks_ be 0.
1. If _largestUnit_ is ~week~, then
1. Let _candidateWeeks_ be _sign_.
1. Set _intermediate_ to BalanceISODate(_constrained_.[[Year]], _constrained_.[[Month]], _constrained_.[[Day]] + 7 × _candidateWeeks_).
1. Repeat, while ISODateSurpasses(_sign_, _intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]], _two_) is *false*,
1. Set _weeks_ to _candidateWeeks_.
1. Set _candidateWeeks_ to _candidateWeeks_ + sign.
1. Set _intermediate_ to BalanceISODate(_intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]] + 7 × _sign_).
1. Let _days_ be 0.
1. Let _candidateDays_ be _sign_.
1. Set _intermediate_ to BalanceISODate(_constrained_.[[Year]], _constrained_.[[Month]], _constrained_.[[Day]] + 7 × _weeks_ + _candidateDays_).
1. Repeat, while ISODateSurpasses(_sign_, _intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]], _two_) is *false*,
1. Set _days_ to _candidateDays_.
1. Set _candidateDays_ to _candidateDays_ + _sign_.
1. Set _intermediate_ to BalanceISODate(_intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]] + _sign_).
1. Return ! CreateDateDurationRecord(_years_, _months_, _weeks_, _days_).
1. Return an implementation-defined Date Duration Record as described above.
1. Let _sign_ be -CompareISODate(_one_, _two_).
1. If _sign_ = 0, return ZeroDateDuration().
Copy link
Collaborator Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Double-check that my signs are correct and not negated.

  1. If one < two:
    1. CompareISODate(one, two) == -1, so sign = 1
    2. Inside the loop, we increment the duration by 1
    3. The loop condition checks CompareISODate(intermediate, two):
      1. The first time, intermediate is one, so the return value is -1, which does not equal sign, so the loop runs
      2. At some point after that, intermediate will be greater than two, at which point the return value is 1, the loop terminates, and the duration is decremented back to the value before the excess occurred
      3. Note: If intermediate and two are ever equal, the loop will run one last time, and the value of duration that caused the two values to be equal will become the resolved duration
  2. If one > two:
    1. CompareISODate(one, two) == 1, so sign == -1
    2. (all other steps should still work, except with signs flipped)

1. Let _duration_ be CreateDateDurationRecord(0, 0, 0, 0).
1. If _largestUnit_ is ~year~, then
1. Let _intermediate_ be _one_.
Copy link
Collaborator Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

_intermediate_ needs to be initialized to something that is on the same side of _two_ as _one_ is, so that the body of the loop runs at least once. I pick _one_ since it always satisfies that criterion.

1. Repeat, while CompareISODate(_intermediate_, _two_) != _sign_,
1. Set _duration_.[[Years]] to _duration_.[[Years]] + _sign_.
1. Set _intermediate_ to CalendarDateAdd(_calendar_, _one_, _duration_, ~constrain~).
1. Set _duration_.[[Years]] to _duration_.[[Years]] - _sign_.
Copy link
Collaborator Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This loop is better written as:

loop {
    duration.years += sign;
    let intermediate = CalendarDateAdd(calendar, one, duration, "constrain");
    if CompareISODate(intermediate, two) == sign {
        duration.years -= sign;
        break;
    }
}

but I wrote it like I did since we don't have do-while loops in ecmarkup.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sure we do:

1. Let _done_ be *false*.
1. Assert: The following loop will terminate.
1. Repeat, while _done_ is *false*,
  1. Set _duration_.[[Years]] to _duration_.[[Years]] + _sign_.
  1. Let _intermediate_ be CalendarDateAdd(_calendar_, _one_, _duration_, ~constrain~).
  1. If CompareISODate(_intermediate_, _two_) is _sign_, then
    1. Set _duration_.[[Years]] to _duration_.[[Years]] - _sign_.
    1. Set _done_ to *true*.

Some examples:

1. If _largestUnit_ is ~year~ or _largestUnit_ is ~month~, then
1. Let _intermediate_ be _one_.
1. Repeat, while CompareISODate(_intermediate_, _two_) != _sign_,
1. Set _duration_.[[Months]] to _duration_.[[Months]] + _sign_.
1. Set _intermediate_ to CalendarDateAdd(_calendar_, _one_, _duration_, ~constrain~).
1. Set _duration_.[[Months]] to _duration_.[[Months]] - _sign_.
1. If _largestUnit_ is ~week~, then
1. Let _intermediate_ be _one_.
1. Repeat, while CompareISODate(_intermediate_, _two_) != _sign_,
1. Set _duration_.[[Weeks]] to _duration_.[[Weeks]] + _sign_.
1. Set _intermediate_ to CalendarDateAdd(_calendar_, _one_, _duration_, ~constrain~).
1. Set _duration_.[[Weeks]] to _duration_.[[Weeks]] - _sign_.
1. Let _intermediate_ be _one_.
1. Repeat, while CompareISODate(_intermediate_, _two_) != _sign_,
1. Set _duration_.[[Days]] to _duration_.[[Days]] + _sign_.
1. Set _intermediate_ to CalendarDateAdd(_calendar_, _one_, _duration_, ~constrain~).
1. Set _duration_.[[Days]] to _duration_.[[Days]] - _sign_.
1. Return ! _duration_.
</emu-alg>
</emu-clause>

Expand Down
Loading