firefox-main/third_party/rust/icu_calendar/src/cal/east_asian_traditional/simple.rs

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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
use super::EastAsianTraditionalYearData;
use calendrical_calculations::{gregorian::DAYS_IN_400_YEAR_CYCLE, rata_die::RataDie};
macro_rules! day_fraction_to_ms {
($n:tt $(/ $d:tt)+) => {{
Milliseconds((MILLISECONDS_IN_EPHEMERIS_DAY as i128 * $n as i128 $( / $d as i128)+) as i64)
}};
($n:tt $(/ $d:tt)+, exact) => {{
let d = day_fraction_to_ms!($n $(/ $d)+);
assert!((d.0 as i128 $(* $d as i128)+) % MILLISECONDS_IN_EPHEMERIS_DAY as i128 == 0, "inexact");
d
}};
}
pub(super) const UTC_PLUS_8: Milliseconds = day_fraction_to_ms!(8 / 24);
pub(super) const UTC_PLUS_9: Milliseconds = day_fraction_to_ms!(9 / 24);
// Reference time was UTC+(1397/180)
pub(super) const BEIJING_UTC_OFFSET: Milliseconds = day_fraction_to_ms!(1397 / 180 / 24);
/// The mean year length according to the Gregorian solar cycle.
const MEAN_GREGORIAN_YEAR_LENGTH: Milliseconds =
day_fraction_to_ms!(DAYS_IN_400_YEAR_CYCLE / 400, exact);
/// The mean solar term length according to the Gregorian solar cycle
const MEAN_GREGORIAN_SOLAR_TERM_LENGTH: Milliseconds =
day_fraction_to_ms!(DAYS_IN_400_YEAR_CYCLE / 400 / 12, exact);
/// The mean synodic length on Jan 1 2000 according to the [Astronomical Almanac (1992)].
///
const MEAN_SYNODIC_MONTH_LENGTH: Milliseconds = day_fraction_to_ms!(295305888531 / 10000000000i64);
/// Number of milliseconds in a day.
const MILLISECONDS_IN_EPHEMERIS_DAY: i64 = 24 * 60 * 60 * 1000;
const UTC_SOLSTICE: LocalMoment = LocalMoment {
rata_die: calendrical_calculations::gregorian::fixed_from_gregorian(1999, 12, 22),
local_milliseconds: ((7 * 60) + 44) * 60 * 1000,
};
const UTC_NEW_MOON: LocalMoment = LocalMoment {
rata_die: calendrical_calculations::gregorian::fixed_from_gregorian(2000, 1, 6),
local_milliseconds: ((18 * 60) + 14) * 60 * 1000,
};
#[derive(Debug, Copy, Clone, Default)]
pub(super) struct Milliseconds(i64);
#[derive(Debug, Copy, Clone)]
struct LocalMoment {
rata_die: RataDie,
local_milliseconds: u32,
}
impl core::ops::Add<Milliseconds> for LocalMoment {
type Output = Self;
fn add(self, Milliseconds(duration): Milliseconds) -> Self::Output {
let temp = self.local_milliseconds as i64 + duration;
Self {
rata_die: self.rata_die + temp.div_euclid(MILLISECONDS_IN_EPHEMERIS_DAY),
local_milliseconds: temp.rem_euclid(MILLISECONDS_IN_EPHEMERIS_DAY) as u32,
}
}
}
impl super::EastAsianTraditionalYearData {
/// A fast approximation for the Chinese calendar, inspired by the _píngqì_ (平氣) rule
/// used in the Ming dynasty.
///
/// Stays anchored in the Gregorian calendar, even as the Gregorian calendar drifts
/// from the seasons in the distant future and distant past.
pub(super) fn simple(
utc_offset: Milliseconds,
related_iso: i32,
) -> EastAsianTraditionalYearData {
/// calculates the largest moment such that moment = base_moment + n * duration lands on rata_die (< rata_die + 1)
fn periodic_duration_on_or_before(
rata_die: RataDie,
base_moment: LocalMoment,
duration: Milliseconds,
) -> LocalMoment {
let diff_millis = (rata_die - base_moment.rata_die) * MILLISECONDS_IN_EPHEMERIS_DAY
- base_moment.local_milliseconds as i64;
let num_periods =
(diff_millis + MILLISECONDS_IN_EPHEMERIS_DAY - 1).div_euclid(duration.0);
let millis = base_moment.rata_die.to_i64_date() * MILLISECONDS_IN_EPHEMERIS_DAY
+ base_moment.local_milliseconds as i64
+ num_periods * duration.0;
// Note: this is Euclidean div/rem, but this more optimized, because
// we know that our divisor is positive
let rata_die = millis / MILLISECONDS_IN_EPHEMERIS_DAY - (millis < 0) as i64;
let local_milliseconds = millis % MILLISECONDS_IN_EPHEMERIS_DAY
+ (millis < 0) as i64 * MILLISECONDS_IN_EPHEMERIS_DAY;
LocalMoment {
rata_die: RataDie::new(rata_die),
local_milliseconds: local_milliseconds as u32,
}
}
let mut major_solar_term = periodic_duration_on_or_before(
calendrical_calculations::iso::day_before_year(related_iso),
UTC_SOLSTICE + utc_offset,
MEAN_GREGORIAN_YEAR_LENGTH,
);
let mut new_moon = periodic_duration_on_or_before(
major_solar_term.rata_die,
UTC_NEW_MOON + utc_offset,
MEAN_SYNODIC_MONTH_LENGTH,
);
let mut next_new_moon = new_moon + MEAN_SYNODIC_MONTH_LENGTH;
// The solstice is in the month of the 11th solar term of the previous year
let mut solar_term = -2;
let mut had_leap_in_sui = false;
// Skip the months before the year (M11, maybe M11L, M12, maybe M12L)
while solar_term < 0
|| (next_new_moon.rata_die <= major_solar_term.rata_die && !had_leap_in_sui)
{
if next_new_moon.rata_die <= major_solar_term.rata_die && !had_leap_in_sui {
had_leap_in_sui = true;
} else {
solar_term += 1;
major_solar_term = major_solar_term + MEAN_GREGORIAN_SOLAR_TERM_LENGTH;
}
(new_moon, next_new_moon) = (next_new_moon, next_new_moon + MEAN_SYNODIC_MONTH_LENGTH);
}
debug_assert_eq!(solar_term, 0);
let start_day = new_moon.rata_die;
let mut month_lengths = [false; 13];
let mut leap_month = None;
// Iterate over the 12 solar terms, producing potentially 13 months
while solar_term < 12
|| (next_new_moon.rata_die <= major_solar_term.rata_die && !had_leap_in_sui)
{
*month_lengths
.get_mut(solar_term as usize + leap_month.is_some() as usize)
.unwrap_or(&mut false) = next_new_moon.rata_die - new_moon.rata_die == 30;
if next_new_moon.rata_die <= major_solar_term.rata_die && !had_leap_in_sui {
had_leap_in_sui = true;
leap_month = Some(solar_term as u8 + 1);
} else {
solar_term += 1;
major_solar_term = major_solar_term + MEAN_GREGORIAN_SOLAR_TERM_LENGTH;
}
(new_moon, next_new_moon) = (next_new_moon, next_new_moon + MEAN_SYNODIC_MONTH_LENGTH);
}
debug_assert_eq!(solar_term, 12);
EastAsianTraditionalYearData::new(related_iso, start_day, month_lengths, leap_month)
}
}
#[test]
fn bounds() {
EastAsianTraditionalYearData::simple(UTC_PLUS_9, 292_277_025);
assert!(
std::panic::catch_unwind(|| EastAsianTraditionalYearData::simple(UTC_PLUS_9, 292_277_026))
.is_err()
);
EastAsianTraditionalYearData::simple(BEIJING_UTC_OFFSET, -292_275_024);
assert!(
std::panic::catch_unwind(|| EastAsianTraditionalYearData::simple(
BEIJING_UTC_OFFSET,
-292_275_025
))
.is_err()
);
}