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[JSC][Temporal] Count lunisolar months in NonISODateUntil from the day span instead of walking them - #606
[JSC][Temporal] Count lunisolar months in NonISODateUntil from the day span instead of walking them#606robobun wants to merge 1 commit into
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Priority: ➖ Normal Merge Risk: 🟡 Moderate · up to The Hebrew long-span stress assertions may perform roughly 49,000 ICU month operations, risking slow runs or timeouts on slower bots; this should be resolved or explicitly accepted before merge. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Heads-up on overlap with #598 (Hijri and Persian years below 1). That PR moves |
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Inline comments:
In `@JSTests/stress/temporal-lunar-calendar-until-months-long-span.js`:
- Around line 114-115: Update the Hebrew long-span cases in checkDifference to
avoid the default single-step month calculation, following the existing
longSpans pattern used for Chinese and Dangi. Add pinned expected month counts
for both Hebrew pairs so coverage remains intact while preventing per-month ICU
operations.
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JSTests/microbenchmarks/temporal-plain-date-until-lunar-months.jsJSTests/stress/temporal-lunar-calendar-until-months-long-span.jsSource/JavaScriptCore/runtime/temporal/core/CalendarICUBridge.cpp
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…ly month count; islamic-* left to #598)
…y span instead of walking them
PlainDate#until and #since with largestUnit "months" in the chinese or
dangi calendar cost about 1 ms per month of span: 1.1 s for a century,
20 s for 0001-01-01 to 2034-02-18, all in one native call on the JS
thread. NonISODateUntil probed one candidate month at a time, and each
probe re-walked the chinese year from M01 to find the ordinal month,
about 30 ICU field resolutions with new-moon and solar-term astronomy
behind each. hebrew took the same loop with cheap steps, still linear
in a span that Temporal allows to reach 6.7 million months.
For the lunisolar calendars (chinese, dangi, hebrew), whose months are
all 29 or 30 days, lunarMonthsBetween now takes the count of whole
months between the two month starts from the epoch-day span over the
calendar's mean month, and confirms it by adding that many months in
ICU from the start month and landing on the target month start. Month
starts never stray from the mean by anything near half a month, so the
first probe lands; a probe that misses steps toward the target, and a
bracket without a landing is an error. Every candidate short of the
target's month stays below it and every one past it surpasses, so this
count decides all candidates but the target's own month, which
surpasses only on the day, the same rule the fixed-solar closed form in
this function already uses. The count no longer needs the ordinal month
of either endpoint, which for chinese/dangi is itself a month walk, so
the snapshot computes it only for the year loop and the fixed-month
paths. Fixed-solar calendars and islamic-* keep their paths through
surpassesMonths, which no lunisolar calendar reaches any more.
chinese 100 years of months: 1120 ms -> 0.3 ms. 0001-01-01 to
2034-02-18: 20 s -> 0.5 ms. Results are unchanged: a differential corpus
of ~90,000 until/since results over eleven calendars matches the old
build except for the hebrew case below, and ICU's add(UCAL_MONTH, n)
was checked against n single steps for chinese and dangi across the
whole +-10000-year range the bridge gives to ICU.
The new path adds many months at once for hebrew too, which ran into an
ICU bug that calendarDateAdd and the old until tail already hit: since
ICU 75, HebrewCalendar::add(UCAL_MONTH, n > 0) fast-forwards whole
19-year cycles by taking multiples of 235 off a month total kept in
UCAL_MONTH slots, where the empty Adar I slot of a common year counts
too. From Adar..Elul of a common year, a result in Tishri..Adar I lands
one month late (5720 Nisan 25 + 463 months gave 5758 Tishri 25 instead
of 5757 Elul 25), so add({ months }) was wrong and until() threw or was
off by one for hebrew spans over 19 years. addCalendarMonths takes the
whole cycles as a year add, where the month slot and its leap status
carry over exactly, and leaves ICU a remainder in [-12, 222] that cannot
reach the fast path. macOS links the system ICU, so patching the bundled
ICU source would not have covered it.
Tests: JSTests/stress/temporal-lunar-calendar-until-months-long-span.js
JSTests/microbenchmarks/temporal-plain-date-until-lunar-months.js
* Source/JavaScriptCore/runtime/temporal/core/CalendarICUBridge.cpp:
(JSC::TemporalCore::addCalendarMonths):
(JSC::TemporalCore::calendarDateAdd):
(JSC::TemporalCore::surpassesMonths):
(JSC::TemporalCore::meanLunarMonthDays):
(JSC::TemporalCore::lunarMonthsBetween):
(JSC::TemporalCore::nonISODateUntil):
* JSTests/stress/temporal-lunar-calendar-until-months-long-span.js: Added.
* JSTests/microbenchmarks/temporal-plain-date-until-lunar-months.js: Added.
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…med to the 200 ms budget; no engine change from cd3f8469)
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Problem
Temporal.PlainDate#until/#sincewithlargestUnit: "months"in thechineseordangicalendar cost about 1 ms per month of span: 100 years took 1.1 s, and0001-01-01to2034-02-18(25,146 months) took 20 s of CPU in one native call. V8 answers the same calls in 0 to 3 ms.nonISODateUntil(Source/JavaScriptCore/runtime/temporal/core/CalendarICUBridge.cpp).surpassesMonthsprobed one month at a time, and for chinese/dangi each probe re-walked the year from M01 (computeFieldResolutionOrdinalMonth) to get an ordinal month: about 30 ICU field resolutions per candidate, each running ICU4C's new-moon and solar-term astronomy.hebrewandislamic-*took the same loop with cheap steps, still linear in a span that can reach 6.7 million months.untiladd many months at once also exposed an ICU bug thatadd({ months })already hit: since ICU 75,HebrewCalendar::add(UCAL_MONTH, n)is one month late forn >= 229from Adar..Elul of a common year when the result lands in Tishri..Adar I (5720 Nisan 25 + 463 monthsgave5758 Tishri 25, not5757 Elul 25). Hebrewuntilover such spans threwRangeErroror was off by one.Fix
lunarMonthsBetween: for the lunisolar calendars (chinese, dangi, hebrew), take the whole-month count between the two month starts from the epoch-day span over the calendar's mean month, then confirm it with one ICU month add from the start month that must land on the target month start (a miss steps toward it, a bracket without a landing is an error). Only the candidate that reaches the target's own month depends on the day, the same rule as the existing fixed-solar closed form. The snapshot's ordinal month is now computed only where the year loop or the fixed-month paths consume it.addCalendarMonths(ICU4C workaround): for hebrew, convert whole 19-year cycles (235 months) into a year add and leave ICU a remainder in [-12, 222], which cannot reach its broken fast path. Used bycalendarDateAdd, theuntiltail and the new probe. macOS links the system ICU, so an ICU source patch would not cover it. It rides in this PR rather than a separate one because the newuntilpath is the first caller that always adds months in bulk; without it the hebrew half of this change would be wrong.surpassesMonths, which no lunisolar calendar reaches any more. islamic-* (twelve months every year) belongs with the fixed-month closed form that [JSC][Temporal] Hijri and Persian years below 1: report the real year and month lengths #598 gives it, so this PR leaves it alone and the two compose in either order.JSTests/stress/temporal-lunar-calendar-until-months-long-span.js(about 100 ms on a releasejsc, with or without JIT; the old build spends minutes in the chinese part and then fails the hebrew add check) andJSTests/microbenchmarks/temporal-plain-date-until-lunar-months.js. AllJSTests/stress/temporal*.js, test262intl402/Temporal(2020 pass, the same 9 ICU-data failures as before) and thebuilt-ins/Temporaluntil/since/add/subtract/round/total subsets (1134 pass) on a releasejscbuilt against ICU 78.3.Background
CalendarDateUntilfor a non-ISO calendar finds the largest number of months whose addition to the earlier date does not pass the later one ("surpass"), comparing year, then month, then the original day. JSC implements non-ISO calendars on ICU4C'sUCalendar(this bridge); V8 uses icu4x, whose dates carry precomputed year data.add(UCAL_MONTH, n)already jumpsnmonths at once through the mean synodic month. Hebrew and islamic months are arithmetic, 29 or 30 days.Notes
0001-01-01..2034-02-1820158 ms -> 0.5 ms; chinese 400ylargestUnit: "years"6.2 ms -> 2.8 ms; hebrew 400y months 48 ms -> 0.01 ms, full Temporal range 0.05 ms. islamic-* is unchanged here (400y 2.6 ms, still linear; [JSC][Temporal] Hijri and Persian years below 1: report the real year and month lengths #598 makes it a closed form). What remains for chinese (0.3 to 1.3 ms) is a handful of ICU field resolutions, each 30 to 240 us in ICU4C'sChineseCalendar.until/sinceresults (11 calendars, both directions, months and years, day-1/day-29/day-30 endpoints, spans up to 400,000 days), plusPlainYearMonth,PlainDateTime,ZonedDateTimedifferences andDuration#round/totalwithrelativeTo. Identical to the old build except hebrew forward spans of 226 months or more, where the old build threw or was off by one; an independent single-step oracle agrees with the new results (chinese, dangi, hebrew: 0 mismatches).add(UCAL_MONTH, n)againstnsingle steps: chinese and dangi, everynup to 247,000 forward from -9998 and backward from +9998 (the whole range the bridge hands to ICU), 0 mismatches. hebrew with the workaround: start years across a full 19-year cycle and at both ends of Temporal's range,nup to 2500 both directions, 0 mismatches (the year-0 Kislev relabel region differs by a day in places, identically before and after).main(MONTHS_IN_CYCLEfast-forward inhebrwcal.cpp, added under ICU-22633); backward adds are not affected.IslamicCalendarcivilLeapYear()uses a truncating%, so every negative islamic year reports a 30-day M12 and a 355-day year. That is what [JSC][Temporal] Hijri and Persian years below 1: report the real year and month lengths #598 fixes.ICU4C-WORKAROUNDcomment describes theHebrewCalendar::addfast-forward precisely enough to file one, and the ICU code is unchanged on ICUmainas of this week.mainhas the identical pre-change file.