Module: CATimeCivil

Defined in:
lib/carray/time.rb

Overview

Internal: unit-conversion algebra shared by CATime / CATimedelta (used by to_comparable to align a search query to the reference unit).

The units split into two groups that are NOT inter-convertible by a fixed ratio: fixed-length (W/D/h/m/s/ms/.../as, ratios in seconds) and calendar (Y/M, ratio in months -- W and below are calendar-dependent in days). Within a group any pair is an exact integer ratio (coarse = fine * N), so a coarse->fine cast is lossless (multiply), and a fine->coarse cast is lossless only when every value is divisible by the divisor. Civil-date arithmetic on int64 CArrays: the calendar kernel every time grid is built on (Howard Hinnant's days<->civil algorithms, vectorized). Internal to the time surface: nothing here is part of the public API.

Class Method Summary collapse

Class Method Details

.civil_from_days(z) ⇒ Object

Vectorized Howard Hinnant civil-date algebra (proleptic Gregorian, negative days supported). days since the Unix epoch -> [year, month, day] int64 CArrays. The algorithm needs the era to floor toward the past, which CArray / does; Hinnant's published form pre-biases the negative operand instead because C truncates.



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# File 'lib/carray/time.rb', line 36

def civil_from_days(z)
  z   = z + 719468
  era = z / 146097
  doe = z - era * 146097
  yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365
  y   = yoe + era * 400
  doy = doe - (365 * yoe + yoe / 4 - yoe / 100)
  mp  = (5 * doy + 2) / 153
  d   = doy - (153 * mp + 2) / 5 + 1       # day of month, 1..31
  m   = mp + (3 - 12 * mp.ge(10))          # mp<10 ? +3 : -9
  [y + m.le(2), m, d]
end

.days_from_civil(y, m, d) ⇒ Object

[year, month, day] int64 CArrays -> days since the Unix epoch.



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# File 'lib/carray/time.rb', line 50

def days_from_civil(y, m, d)
  y   = y - m.le(2)
  era = y / 400
  yoe = y - era * 400
  doy = (153 * (m + (9 - 12 * m.gt(2))) + 2) / 5 + (d - 1)  # m>2 ? -3 : +9
  doe = yoe * 365 + yoe / 4 - yoe / 100 + doy
  era * 146097 + doe - 719468
end