mozilla-central/third_party/rust/calendrical_calculations/src/chinese_based.rs

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use crate::astronomy::{self, Astronomical, Location, MEAN_SYNODIC_MONTH, MEAN_TROPICAL_YEAR};
use crate::helpers::i64_to_i32;
use crate::iso::{fixed_from_iso, iso_from_fixed};
use crate::rata_die::{Moment, RataDie};
use core::num::NonZeroU8;
#[allow(unused_imports)]
use core_maths::*;
// Don't iterate more than 14 times (which accounts for checking for 13 months)
const MAX_ITERS_FOR_MONTHS_OF_YEAR: u8 = 14;
/// The trait ChineseBased is used by Chinese-based calendars to perform computations shared by such calendar.
/// To do so, calendars should:
///
/// - Implement `fn location` by providing a location at which observations of the moon are recorded, which
/// may change over time (the zone is important, long, lat, and elevation are not relevant for these calculations)
/// - Define `const EPOCH` as a `RataDie` marking the start date of the era of the Calendar for internal use,
/// which may not accurately reflect how years or eras are marked traditionally or seen by end-users
pub trait ChineseBased {
/// Given a fixed date, return the location used for observations of the new moon in order to
/// calculate the beginning of months. For multiple Chinese-based lunar calendars, this has
/// changed over the years, and can cause differences in calendar date.
fn location(fixed: RataDie) -> Location;
/// The RataDie of the beginning of the epoch used for internal computation; this may not
/// reflect traditional methods of year-tracking or eras, since Chinese-based calendars
/// may not track years ordinally in the same way many western calendars do.
const EPOCH: RataDie;
/// The ISO year that corresponds to year 1
const EPOCH_ISO: i32;
/// The name of the calendar for debugging.
const DEBUG_NAME: &'static str;
/// Given an ISO year, return the extended year
fn extended_from_iso(iso_year: i32) -> i32 {
iso_year - Self::EPOCH_ISO + 1
}
/// Given an extended year, return the ISO year
fn iso_from_extended(extended_year: i32) -> i32 {
extended_year - 1 + Self::EPOCH_ISO
}
}
// The equivalent first day in the Chinese calendar (based on inception of the calendar)
const CHINESE_EPOCH: RataDie = RataDie::new(-963099); // Feb. 15, 2637 BCE (-2636)
const CHINESE_EPOCH_ISO: i32 = -2636;
/// The Chinese calendar relies on knowing the current day at the moment of a new moon;
/// however, this can vary depending on location. As such, new moon calculations are based
/// on the time in Beijing. Before 1929, local time was used, represented as UTC+(1397/180 h).
/// In 1929, China adopted a standard time zone based on 120 degrees of longitude, meaning
/// from 1929 onward, all new moon calculations are based on UTC+8h.
///
/// Offsets are not given in hours, but in partial days (1 hour = 1 / 24 day)
const UTC_OFFSET_PRE_1929: f64 = (1397.0 / 180.0) / 24.0;
const UTC_OFFSET_POST_1929: f64 = 8.0 / 24.0;
const CHINESE_LOCATION_PRE_1929: Location =
Location::new_unchecked(39.0, 116.0, 43.5, UTC_OFFSET_PRE_1929);
const CHINESE_LOCATION_POST_1929: Location =
Location::new_unchecked(39.0, 116.0, 43.5, UTC_OFFSET_POST_1929);
// The first day in the Korean Dangi calendar (based on the founding of Gojoseon)
const KOREAN_EPOCH: RataDie = RataDie::new(-852065); // Lunar new year 2333 BCE (-2332 ISO)
const KOREAN_EPOCH_ISO: i32 = -2332; // Lunar new year 2333 BCE (-2332 ISO)
/// The Korean Dangi calendar relies on knowing the current day at the moment of a new moon;
/// however, this can vary depending on location. As such, new moon calculations are based on
/// the time in Seoul. Before 1908, local time was used, represented as UTC+(3809/450 h).
/// This changed multiple times as different standard timezones were adopted in Korea.
/// Currently, UTC+9h is used.
///
/// Offsets are not given in hours, but in partial days (1 hour = 1 / 24 day).
const UTC_OFFSET_ORIGINAL: f64 = (3809.0 / 450.0) / 24.0;
const UTC_OFFSET_1908: f64 = 8.5 / 24.0;
const UTC_OFFSET_1912: f64 = 9.0 / 24.0;
const UTC_OFFSET_1954: f64 = 8.5 / 24.0;
const UTC_OFFSET_1961: f64 = 9.0 / 24.0;
const FIXED_1908: RataDie = RataDie::new(696608); // Apr 1, 1908
const FIXED_1912: RataDie = RataDie::new(697978); // Jan 1, 1912
const FIXED_1954: RataDie = RataDie::new(713398); // Mar 21, 1954
const FIXED_1961: RataDie = RataDie::new(716097); // Aug 10, 1961
const KOREAN_LATITUDE: f64 = 37.0 + (34.0 / 60.0);
const KOREAN_LONGITUDE: f64 = 126.0 + (58.0 / 60.0);
const KOREAN_ELEVATION: f64 = 0.0;
const KOREAN_LOCATION_ORIGINAL: Location = Location::new_unchecked(
KOREAN_LATITUDE,
KOREAN_LONGITUDE,
KOREAN_ELEVATION,
UTC_OFFSET_ORIGINAL,
);
const KOREAN_LOCATION_1908: Location = Location::new_unchecked(
KOREAN_LATITUDE,
KOREAN_LONGITUDE,
KOREAN_ELEVATION,
UTC_OFFSET_1908,
);
const KOREAN_LOCATION_1912: Location = Location::new_unchecked(
KOREAN_LATITUDE,
KOREAN_LONGITUDE,
KOREAN_ELEVATION,
UTC_OFFSET_1912,
);
const KOREAN_LOCATION_1954: Location = Location::new_unchecked(
KOREAN_LATITUDE,
KOREAN_LONGITUDE,
KOREAN_ELEVATION,
UTC_OFFSET_1954,
);
const KOREAN_LOCATION_1961: Location = Location::new_unchecked(
KOREAN_LATITUDE,
KOREAN_LONGITUDE,
KOREAN_ELEVATION,
UTC_OFFSET_1961,
);
/// A type implementing [`ChineseBased`] for the Chinese calendar
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Default, Hash)]
#[allow(clippy::exhaustive_structs)] // newtype
pub struct Chinese;
/// A type implementing [`ChineseBased`] for the Dangi (Korean) calendar
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Default, Hash)]
#[allow(clippy::exhaustive_structs)] // newtype
pub struct Dangi;
impl ChineseBased for Chinese {
fn location(fixed: RataDie) -> Location {
let year = crate::iso::iso_year_from_fixed(fixed);
if year < 1929 {
CHINESE_LOCATION_PRE_1929
} else {
CHINESE_LOCATION_POST_1929
}
}
const EPOCH: RataDie = CHINESE_EPOCH;
const EPOCH_ISO: i32 = CHINESE_EPOCH_ISO;
const DEBUG_NAME: &'static str = "chinese";
}
impl ChineseBased for Dangi {
fn location(fixed: RataDie) -> Location {
if fixed < FIXED_1908 {
KOREAN_LOCATION_ORIGINAL
} else if fixed < FIXED_1912 {
KOREAN_LOCATION_1908
} else if fixed < FIXED_1954 {
KOREAN_LOCATION_1912
} else if fixed < FIXED_1961 {
KOREAN_LOCATION_1954
} else {
KOREAN_LOCATION_1961
}
}
const EPOCH: RataDie = KOREAN_EPOCH;
const EPOCH_ISO: i32 = KOREAN_EPOCH_ISO;
const DEBUG_NAME: &'static str = "dangi";
}
/// Marks the bounds of a lunar year
#[derive(Debug, Copy, Clone)]
#[allow(clippy::exhaustive_structs)] // we're comfortable making frequent breaking changes to this crate
pub struct YearBounds {
/// The date marking the start of the current lunar year
pub new_year: RataDie,
/// The date marking the start of the next lunar year
pub next_new_year: RataDie,
}
impl YearBounds {
/// Compute the YearBounds for the lunar year (å¹´) containing `date`,
/// as well as the corresponding solar year (æ­²). Note that since the two
/// years overlap significantly but not entirely, the solstice bounds for the solar
/// year *may* not include `date`.
#[inline]
pub fn compute<C: ChineseBased>(date: RataDie) -> Self {
let prev_solstice = winter_solstice_on_or_before::<C>(date);
let (new_year, next_solstice) = new_year_on_or_before_fixed_date::<C>(date, prev_solstice);
// Using 400 here since new years can be up to 390 days apart, and we add some padding
let next_new_year = new_year_on_or_before_fixed_date::<C>(new_year + 400, next_solstice).0;
Self {
new_year,
next_new_year,
}
}
/// The number of days in this year
pub fn count_days(self) -> u16 {
let result = self.next_new_year - self.new_year;
debug_assert!(
((u16::MIN as i64)..=(u16::MAX as i64)).contains(&result),
"Days in year should be in range of u16."
);
result as u16
}
/// Whether or not this is a leap year
pub fn is_leap(self) -> bool {
let difference = self.next_new_year - self.new_year;
difference > 365
}
}
/// Get the current major solar term of a fixed date, output as an integer from 1..=12.
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn major_solar_term_from_fixed<C: ChineseBased>(date: RataDie) -> u32 {
let moment: Moment = date.as_moment();
let location = C::location(date);
let universal: Moment = Location::universal_from_standard(moment, location);
let solar_longitude =
i64_to_i32(Astronomical::solar_longitude(Astronomical::julian_centuries(universal)) as i64);
debug_assert!(
solar_longitude.is_ok(),
"Solar longitude should be in range of i32"
);
let s = solar_longitude.unwrap_or_else(|e| e.saturate());
let result_signed = (2 + s.div_euclid(30) - 1).rem_euclid(12) + 1;
debug_assert!(result_signed >= 0);
result_signed as u32
}
/// The fixed date in standard time at the observation location of the next new moon on or after a given Moment.
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn new_moon_on_or_after<C: ChineseBased>(moment: Moment) -> RataDie {
let new_moon_moment = Astronomical::new_moon_at_or_after(midnight::<C>(moment));
let location = C::location(new_moon_moment.as_rata_die());
Location::standard_from_universal(new_moon_moment, location).as_rata_die()
}
/// The fixed date in standard time at the observation location of the previous new moon before a given Moment.
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn new_moon_before<C: ChineseBased>(moment: Moment) -> RataDie {
let new_moon_moment = Astronomical::new_moon_before(midnight::<C>(moment));
let location = C::location(new_moon_moment.as_rata_die());
Location::standard_from_universal(new_moon_moment, location).as_rata_die()
}
/// Universal time of midnight at start of a Moment's day at the observation location
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn midnight<C: ChineseBased>(moment: Moment) -> Moment {
Location::universal_from_standard(moment, C::location(moment.as_rata_die()))
}
/// Determines the fixed date of the lunar new year given the start of its corresponding solar year (æ­²), which is
/// also the winter solstice
///
/// Calls to `no_major_solar_term` have been inlined for increased efficiency.
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn new_year_in_sui<C: ChineseBased>(prior_solstice: RataDie) -> (RataDie, RataDie) {
// s1 is prior_solstice
// Using 370 here since solstices are ~365 days apart
// Both solstices should fall on December 20, 21, 22, or 23. The calendrical calculations
// drift away from this for large positive and negative years, so we artifically bind them
// to this range in order for other code invariants to be upheld.
let prior_solstice = bind_winter_solstice::<C>(prior_solstice);
let following_solstice =
bind_winter_solstice::<C>(winter_solstice_on_or_before::<C>(prior_solstice + 370)); // s2
let month_after_eleventh = new_moon_on_or_after::<C>((prior_solstice + 1).as_moment()); // m12
debug_assert!(month_after_eleventh - prior_solstice >= 0);
let month_after_twelfth = new_moon_on_or_after::<C>((month_after_eleventh + 1).as_moment()); // m13
let month_after_thirteenth = new_moon_on_or_after::<C>((month_after_twelfth + 1).as_moment());
debug_assert!(month_after_twelfth - month_after_eleventh >= 29);
let next_eleventh_month = new_moon_before::<C>((following_solstice + 1).as_moment()); // next-m11
let lhs_argument =
((next_eleventh_month - month_after_eleventh) as f64 / MEAN_SYNODIC_MONTH).round() as i64;
let solar_term_a = major_solar_term_from_fixed::<C>(month_after_eleventh);
let solar_term_b = major_solar_term_from_fixed::<C>(month_after_twelfth);
let solar_term_c = major_solar_term_from_fixed::<C>(month_after_thirteenth);
if lhs_argument == 12 && (solar_term_a == solar_term_b || solar_term_b == solar_term_c) {
(month_after_thirteenth, following_solstice)
} else {
(month_after_twelfth, following_solstice)
}
}
/// This function forces the RataDie to be on December 20, 21, 22, or 23. It was
/// created for practical considerations and is not in the text.
///
fn bind_winter_solstice<C: ChineseBased>(solstice: RataDie) -> RataDie {
let (iso_year, iso_month, iso_day) = match iso_from_fixed(solstice) {
Ok(ymd) => ymd,
Err(_) => {
debug_assert!(false, "Solstice REALLY out of bounds: {solstice:?}");
return solstice;
}
};
let resolved_solstice = if iso_month < 12 || iso_day < 20 {
fixed_from_iso(iso_year, 12, 20)
} else if iso_day > 23 {
fixed_from_iso(iso_year, 12, 23)
} else {
solstice
};
if resolved_solstice != solstice {
if !(0..=4000).contains(&iso_year) {
#[cfg(feature = "logging")]
log::trace!("({}) Solstice out of bounds: {solstice:?}", C::DEBUG_NAME);
} else {
debug_assert!(
false,
"({}) Solstice out of bounds: {solstice:?}",
C::DEBUG_NAME
);
}
}
resolved_solstice
}
/// Get the fixed date of the nearest winter solstice, in the Chinese time zone,
/// on or before a given fixed date.
///
/// This is valid for several thousand years, but it drifts for large positive
/// and negative years. See [`bind_winter_solstice`].
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn winter_solstice_on_or_before<C: ChineseBased>(date: RataDie) -> RataDie {
let approx = Astronomical::estimate_prior_solar_longitude(
astronomy::WINTER,
midnight::<C>((date + 1).as_moment()),
);
let mut iters = 0;
let mut day = Moment::new((approx.inner() - 1.0).floor());
while iters < MAX_ITERS_FOR_MONTHS_OF_YEAR
&& astronomy::WINTER
>= Astronomical::solar_longitude(Astronomical::julian_centuries(midnight::<C>(
day + 1.0,
)))
{
iters += 1;
day += 1.0;
}
debug_assert!(
iters < MAX_ITERS_FOR_MONTHS_OF_YEAR,
"Number of iterations was higher than expected"
);
day.as_rata_die()
}
/// Get the fixed date of the nearest Lunar New Year on or before a given fixed date.
/// This function also returns the solstice following a given date for optimization (see #3743).
///
/// To call this function you must precompute the value of the prior solstice, which
/// is the result of winter_solstice_on_or_before
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz.
pub(crate) fn new_year_on_or_before_fixed_date<C: ChineseBased>(
date: RataDie,
prior_solstice: RataDie,
) -> (RataDie, RataDie) {
let new_year = new_year_in_sui::<C>(prior_solstice);
if date >= new_year.0 {
new_year
} else {
// This happens when we're at the end of the current lunar year
// and the solstice has already happened. Thus the relevant solstice
// for the current lunar year is the previous one, which we calculate by offsetting
// back by a year.
let date_in_last_sui = date - 180; // This date is in the current lunar year, but the last solar year
let prior_solstice = winter_solstice_on_or_before::<C>(date_in_last_sui);
new_year_in_sui::<C>(prior_solstice)
}
}
/// Get a RataDie in the middle of a year; this is not necessarily meant for direct use in
/// calculations; rather, it is useful for getting a RataDie guaranteed to be in a given year
/// as input for other calculations like calculating the leap month in a year.
///
/// Based on functions from _Calendrical Calculations_ by Reingold & Dershowitz
pub fn fixed_mid_year_from_year<C: ChineseBased>(elapsed_years: i32) -> RataDie {
let cycle = (elapsed_years - 1).div_euclid(60) + 1;
let year = (elapsed_years - 1).rem_euclid(60) + 1;
C::EPOCH + ((((cycle - 1) * 60 + year - 1) as f64 + 0.5) * MEAN_TROPICAL_YEAR) as i64
}
/// Whether this year is a leap year
pub fn is_leap_year<C: ChineseBased>(year: i32) -> bool {
let mid_year = fixed_mid_year_from_year::<C>(year);
YearBounds::compute::<C>(mid_year).is_leap()
}
/// The last month and day in this year
pub fn last_month_day_in_year<C: ChineseBased>(year: i32) -> (u8, u8) {
let mid_year = fixed_mid_year_from_year::<C>(year);
let year_bounds = YearBounds::compute::<C>(mid_year);
let last_day = year_bounds.next_new_year - 1;
let month = if year_bounds.is_leap() { 13 } else { 12 };
let day = last_day - new_moon_before::<C>(last_day.as_moment()) + 1;
(month, day as u8)
}
/// Calculated the numbers of days in the given year
pub fn days_in_provided_year<C: ChineseBased>(year: i32) -> u16 {
let mid_year = fixed_mid_year_from_year::<C>(year);
let bounds = YearBounds::compute::<C>(mid_year);
bounds.count_days()
}
/// chinese_based_date_from_fixed returns extra things for use in caching
#[derive(Debug)]
#[non_exhaustive]
pub struct ChineseFromFixedResult {
/// The chinese year
pub year: i32,
/// The chinese month
pub month: u8,
/// The chinese day
pub day: u8,
/// The bounds of the current lunar year
pub year_bounds: YearBounds,
/// The index of the leap month, if any
pub leap_month: Option<NonZeroU8>,
}
/// Get a chinese based date from a fixed date, with the related ISO year
///
/// Months are calculated by iterating through the dates of new moons until finding the last month which
/// does not exceed the given fixed date. The day of month is calculated by subtracting the fixed date
/// from the fixed date of the beginning of the month.
///
/// The calculation for `elapsed_years` and `month` in this function are based on code from _Calendrical Calculations_ by Reingold & Dershowitz.
pub fn chinese_based_date_from_fixed<C: ChineseBased>(date: RataDie) -> ChineseFromFixedResult {
let year_bounds = YearBounds::compute::<C>(date);
let first_day_of_year = year_bounds.new_year;
let year_float =
(1.5 - 1.0 / 12.0 + ((first_day_of_year - C::EPOCH) as f64) / MEAN_TROPICAL_YEAR).floor();
let year_int = i64_to_i32(year_float as i64);
debug_assert!(year_int.is_ok(), "Year should be in range of i32");
let year = year_int.unwrap_or_else(|e| e.saturate());
let new_moon = new_moon_before::<C>((date + 1).as_moment());
let month_i64 = ((new_moon - first_day_of_year) as f64 / MEAN_SYNODIC_MONTH).round() as i64 + 1;
debug_assert!(
((u8::MIN as i64)..=(u8::MAX as i64)).contains(&month_i64),
"Month should be in range of u8! Value {month_i64} failed for RD {date:?}"
);
let month = month_i64 as u8;
let day_i64 = date - new_moon + 1;
debug_assert!(
((u8::MIN as i64)..=(u8::MAX as i64)).contains(&month_i64),
"Day should be in range of u8! Value {month_i64} failed for RD {date:?}"
);
let day = day_i64 as u8;
let leap_month = if year_bounds.is_leap() {
// This doesn't need to be checked for `None`, since `get_leap_month_from_new_year`
// will always return a number greater than or equal to 1, and less than 14.
NonZeroU8::new(get_leap_month_from_new_year::<C>(first_day_of_year))
} else {
None
};
ChineseFromFixedResult {
year,
month,
day,
year_bounds,
leap_month,
}
}
/// Given that `new_year` is the first day of a leap year, find which month in the year is a leap month.
/// Since the first month in which there are no major solar terms is a leap month, this function
/// cycles through months until it finds the leap month, then returns the number of that month. This
/// function assumes the date passed in is in a leap year and tests to ensure this is the case in debug
/// mode by asserting that no more than thirteen months are analyzed.
///
/// Calls to `no_major_solar_term` have been inlined for increased efficiency.
///
/// Conceptually similar to code from _Calendrical Calculations_ by Reingold & Dershowitz
pub fn get_leap_month_from_new_year<C: ChineseBased>(new_year: RataDie) -> u8 {
let mut cur = new_year;
let mut result = 1;
let mut solar_term = major_solar_term_from_fixed::<C>(cur);
loop {
let next = new_moon_on_or_after::<C>((cur + 1).as_moment());
let next_solar_term = major_solar_term_from_fixed::<C>(next);
if result >= MAX_ITERS_FOR_MONTHS_OF_YEAR || solar_term == next_solar_term {
break;
}
cur = next;
solar_term = next_solar_term;
result += 1;
}
debug_assert!(result < MAX_ITERS_FOR_MONTHS_OF_YEAR, "The given year was not a leap year and an unexpected number of iterations occurred searching for a leap month.");
result
}
/// Returns the number of days in the given (year, month). In the Chinese calendar, months start at each
/// new moon, so this function finds the number of days between the new moon at the beginning of the given
/// month and the new moon at the beginning of the next month.
pub fn month_days<C: ChineseBased>(year: i32, month: u8) -> u8 {
let mid_year = fixed_mid_year_from_year::<C>(year);
let prev_solstice = winter_solstice_on_or_before::<C>(mid_year);
let new_year = new_year_on_or_before_fixed_date::<C>(mid_year, prev_solstice).0;
days_in_month::<C>(month, new_year, None).0
}
/// Returns the number of days in the given `month` after the given `new_year`.
/// Also returns the RataDie of the new moon beginning the next month.
pub fn days_in_month<C: ChineseBased>(
month: u8,
new_year: RataDie,
prev_new_moon: Option<RataDie>,
) -> (u8, RataDie) {
let approx = new_year + ((month - 1) as i64 * 29);
let prev_new_moon = if let Some(prev_moon) = prev_new_moon {
prev_moon
} else {
new_moon_before::<C>((approx + 15).as_moment())
};
let next_new_moon = new_moon_on_or_after::<C>((approx + 15).as_moment());
let result = (next_new_moon - prev_new_moon) as u8;
debug_assert!(result == 29 || result == 30);
(result, next_new_moon)
}
/// Given a new year, calculate the number of days in the previous year
pub fn days_in_prev_year<C: ChineseBased>(new_year: RataDie) -> u16 {
let date = new_year - 300;
let prev_solstice = winter_solstice_on_or_before::<C>(date);
let (prev_new_year, _) = new_year_on_or_before_fixed_date::<C>(date, prev_solstice);
u16::try_from(new_year - prev_new_year).unwrap_or(360)
}
/// Returns the length of each month in the year, as well as a leap month index (1-indexed) if any.
/// Month lengths are stored as true for 30-day, false for 29-day.
/// In the case of no leap months, month 13 will have value false.
pub fn month_structure_for_year<C: ChineseBased>(
new_year: RataDie,
next_new_year: RataDie,
) -> ([bool; 13], Option<NonZeroU8>) {
let mut ret = [false; 13];
let mut current_month_start = new_year;
let mut current_month_major_solar_term = major_solar_term_from_fixed::<C>(new_year);
let mut leap_month_index = None;
for i in 0u8..12 {
let next_month_start = new_moon_on_or_after::<C>((current_month_start + 28).as_moment());
let next_month_major_solar_term = major_solar_term_from_fixed::<C>(next_month_start);
if next_month_major_solar_term == current_month_major_solar_term {
leap_month_index = NonZeroU8::new(i + 1);
}
let diff = next_month_start - current_month_start;
debug_assert!(diff == 29 || diff == 30);
#[allow(clippy::indexing_slicing)] // array is of length 13, we iterate till i=11
if diff == 30 {
ret[usize::from(i)] = true;
}
current_month_start = next_month_start;
current_month_major_solar_term = next_month_major_solar_term;
}
if current_month_start == next_new_year {
// not all months without solar terms are leap months; they are only leap months if
// the year can admit them
//
// From Reingold & Dershowitz (p 311):
//
// The leap month of a 13-month winter-solstice-to-winter-solstice period is the first month
// that does not contain a major solar term — that is, the first lunar month that is wholly within a solar month.
//
// As such, if a month without a solar term is found in a non-leap year, we just ingnore it.
leap_month_index = None;
} else {
let diff = next_new_year - current_month_start;
debug_assert!(diff == 29 || diff == 30);
if diff == 30 {
ret[12] = true;
}
}
if current_month_start != next_new_year && leap_month_index.is_none() {
leap_month_index = NonZeroU8::new(13); // The last month is a leap month
debug_assert!(
major_solar_term_from_fixed::<C>(current_month_start) == current_month_major_solar_term,
"A leap month is required here, but it had a major solar term!"
);
}
(ret, leap_month_index)
}
/// Given the new year and a month/day pair, calculate the number of days until the first day of the given month
pub fn days_until_month<C: ChineseBased>(new_year: RataDie, month: u8) -> u16 {
let month_approx = 28_u16.saturating_mul(u16::from(month) - 1);
let new_moon = new_moon_on_or_after::<C>(new_year.as_moment() + (month_approx as f64));
let result = new_moon - new_year;
debug_assert!(((u16::MIN as i64)..=(u16::MAX as i64)).contains(&result), "Result {result} from new moon: {new_moon:?} and new year: {new_year:?} should be in range of u16!");
result as u16
}
#[cfg(test)]
mod test {
use super::*;
use crate::rata_die::Moment;
#[test]
fn test_chinese_new_moon_directionality() {
for i in (-1000..1000).step_by(31) {
let moment = Moment::new(i as f64);
let before = new_moon_before::<Chinese>(moment);
let after = new_moon_on_or_after::<Chinese>(moment);
assert!(before < after, "Chinese new moon directionality failed for Moment: {moment:?}, with:\n\tBefore: {before:?}\n\tAfter: {after:?}");
}
}
#[test]
fn test_chinese_new_year_on_or_before() {
let fixed = crate::iso::fixed_from_iso(2023, 6, 22);
let prev_solstice = winter_solstice_on_or_before::<Chinese>(fixed);
let result_fixed = new_year_on_or_before_fixed_date::<Chinese>(fixed, prev_solstice).0;
let (y, m, d) = crate::iso::iso_from_fixed(result_fixed).unwrap();
assert_eq!(y, 2023);
assert_eq!(m, 1);
assert_eq!(d, 22);
}
fn seollal_on_or_before(fixed: RataDie) -> RataDie {
let prev_solstice = winter_solstice_on_or_before::<Dangi>(fixed);
new_year_on_or_before_fixed_date::<Dangi>(fixed, prev_solstice).0
}
#[test]
fn test_month_structure() {
// Mostly just tests that the assertions aren't hit
for year in 1900..2050 {
let fixed = crate::iso::fixed_from_iso(year, 1, 1);
let chinese_year = chinese_based_date_from_fixed::<Chinese>(fixed);
let (month_lengths, leap) = month_structure_for_year::<Chinese>(
chinese_year.year_bounds.new_year,
chinese_year.year_bounds.next_new_year,
);
for (i, month_is_30) in month_lengths.into_iter().enumerate() {
if leap.is_none() && i == 12 {
// month_days has no defined behavior for month 13 on non-leap-years
continue;
}
let month_len = 29 + i32::from(month_is_30);
let month_days = month_days::<Chinese>(chinese_year.year, i as u8 + 1);
assert_eq!(
month_len,
i32::from(month_days),
"Month length for month {} must be the same",
i + 1
);
}
println!(
"{year} (chinese {}): {month_lengths:?} {leap:?}",
chinese_year.year
);
}
}
#[test]
fn test_seollal() {
#[derive(Debug)]
struct TestCase {
iso_year: i32,
iso_month: u8,
iso_day: u8,
expected_year: i32,
expected_month: u8,
expected_day: u8,
}
let cases = [
TestCase {
iso_year: 2024,
iso_month: 6,
iso_day: 6,
expected_year: 2024,
expected_month: 2,
expected_day: 10,
},
TestCase {
iso_year: 2024,
iso_month: 2,
iso_day: 9,
expected_year: 2023,
expected_month: 1,
expected_day: 22,
},
TestCase {
iso_year: 2023,
iso_month: 1,
iso_day: 22,
expected_year: 2023,
expected_month: 1,
expected_day: 22,
},
TestCase {
iso_year: 2023,
iso_month: 1,
iso_day: 21,
expected_year: 2022,
expected_month: 2,
expected_day: 1,
},
TestCase {
iso_year: 2022,
iso_month: 6,
iso_day: 6,
expected_year: 2022,
expected_month: 2,
expected_day: 1,
},
TestCase {
iso_year: 2021,
iso_month: 6,
iso_day: 6,
expected_year: 2021,
expected_month: 2,
expected_day: 12,
},
TestCase {
iso_year: 2020,
iso_month: 6,
iso_day: 6,
expected_year: 2020,
expected_month: 1,
expected_day: 25,
},
TestCase {
iso_year: 2019,
iso_month: 6,
iso_day: 6,
expected_year: 2019,
expected_month: 2,
expected_day: 5,
},
TestCase {
iso_year: 2018,
iso_month: 6,
iso_day: 6,
expected_year: 2018,
expected_month: 2,
expected_day: 16,
},
TestCase {
iso_year: 2025,
iso_month: 6,
iso_day: 6,
expected_year: 2025,
expected_month: 1,
expected_day: 29,
},
TestCase {
iso_year: 2026,
iso_month: 8,
iso_day: 8,
expected_year: 2026,
expected_month: 2,
expected_day: 17,
},
TestCase {
iso_year: 2027,
iso_month: 4,
iso_day: 4,
expected_year: 2027,
expected_month: 2,
expected_day: 7,
},
TestCase {
iso_year: 2028,
iso_month: 9,
iso_day: 21,
expected_year: 2028,
expected_month: 1,
expected_day: 27,
},
];
for case in cases {
let fixed = crate::iso::fixed_from_iso(case.iso_year, case.iso_month, case.iso_day);
let seollal = seollal_on_or_before(fixed);
let (y, m, d) = crate::iso::iso_from_fixed(seollal).unwrap();
assert_eq!(
y, case.expected_year,
"Year check failed for case: {case:?}"
);
assert_eq!(
m, case.expected_month,
"Month check failed for case: {case:?}"
);
assert_eq!(d, case.expected_day, "Day check failed for case: {case:?}");
}
}
}