Bug: Speed-up date-time rebasing
Status: Resolved | Priority: Major | Resolution: Fixed
Created: 29/Mar/20 11:30
Affects Version/s: 3.0.0

I do believe it is possible to speed up date-time rebasing by building a map of micros to diffs between original and rebased micros. And look up at the map via binary search.

For example, the *America/Los_Angeles* time zone has less than 100 points when diff changes:
{code:scala}
  test("optimize rebasing") {
    val start = instantToMicros(LocalDateTime.of(1, 1, 1, 0, 0, 0)
      .atZone(getZoneId("America/Los_Angeles"))
      .toInstant)
    val end = instantToMicros(LocalDateTime.of(2030, 1, 1, 0, 0, 0)
      .atZone(getZoneId("America/Los_Angeles"))
      .toInstant)

    var micros = start
    var diff = Long.MaxValue
    var counter = 0
    while (micros < end) {
      val rebased = rebaseGregorianToJulianMicros(micros)
      val curDiff = rebased - micros
      if (curDiff != diff) {
        counter += 1
        diff = curDiff
        val ldt = microsToInstant(micros).atZone(getZoneId("America/Los_Angeles")).toLocalDateTime
        println(s"local date-time = $ldt diff = ${diff / MICROS_PER_MINUTE} minutes")
      }
      micros += MICROS_PER_HOUR
    }
    println(s"counter = $counter")
  }
{code}
{code:java}
local date-time = 0001-01-01T00:00 diff = -2909 minutes
local date-time = 0100-02-28T14:00 diff = -1469 minutes
local date-time = 0200-02-28T14:00 diff = -29 minutes
local date-time = 0300-02-28T14:00 diff = 1410 minutes
local date-time = 0500-02-28T14:00 diff = 2850 minutes
local date-time = 0600-02-28T14:00 diff = 4290 minutes
local date-time = 0700-02-28T14:00 diff = 5730 minutes
local date-time = 0900-02-28T14:00 diff = 7170 minutes
local date-time = 1000-02-28T14:00 diff = 8610 minutes
local date-time = 1100-02-28T14:00 diff = 10050 minutes
local date-time = 1300-02-28T14:00 diff = 11490 minutes
local date-time = 1400-02-28T14:00 diff = 12930 minutes
local date-time = 1500-02-28T14:00 diff = 14370 minutes
local date-time = 1582-10-14T14:00 diff = -29 minutes
local date-time = 1899-12-31T16:52:58 diff = 0 minutes
local date-time = 1917-12-27T11:52:58 diff = 60 minutes
local date-time = 1917-12-27T12:52:58 diff = 0 minutes
local date-time = 1918-09-15T12:52:58 diff = 60 minutes
local date-time = 1918-09-15T13:52:58 diff = 0 minutes
local date-time = 1919-06-30T16:52:58 diff = 31 minutes
local date-time = 1919-06-30T17:52:58 diff = 0 minutes
local date-time = 1919-08-15T12:52:58 diff = 60 minutes
local date-time = 1919-08-15T13:52:58 diff = 0 minutes
local date-time = 1921-08-31T10:52:58 diff = 60 minutes
local date-time = 1921-08-31T11:52:58 diff = 0 minutes
local date-time = 1921-09-30T11:52:58 diff = 60 minutes
local date-time = 1921-09-30T12:52:58 diff = 0 minutes
local date-time = 1922-09-30T12:52:58 diff = 60 minutes
local date-time = 1922-09-30T13:52:58 diff = 0 minutes
local date-time = 1981-09-30T12:52:58 diff = 60 minutes
local date-time = 1981-09-30T13:52:58 diff = 0 minutes
local date-time = 1982-09-30T12:52:58 diff = 60 minutes
local date-time = 1982-09-30T13:52:58 diff = 0 minutes
local date-time = 1983-09-30T12:52:58 diff = 60 minutes
local date-time = 1983-09-30T13:52:58 diff = 0 minutes
local date-time = 1984-09-29T15:52:58 diff = 60 minutes
local date-time = 1984-09-29T16:52:58 diff = 0 minutes
local date-time = 1985-09-28T15:52:58 diff = 60 minutes
local date-time = 1985-09-28T16:52:58 diff = 0 minutes
local date-time = 1986-09-27T15:52:58 diff = 60 minutes
local date-time = 1986-09-27T16:52:58 diff = 0 minutes
local date-time = 1987-09-26T15:52:58 diff = 60 minutes
local date-time = 1987-09-26T16:52:58 diff = 0 minutes
local date-time = 1988-09-24T15:52:58 diff = 60 minutes
local date-time = 1988-09-24T16:52:58 diff = 0 minutes
local date-time = 1989-09-23T15:52:58 diff = 60 minutes
local date-time = 1989-09-23T16:52:58 diff = 0 minutes
local date-time = 1990-09-29T15:52:58 diff = 60 minutes
local date-time = 1990-09-29T16:52:58 diff = 0 minutes
local date-time = 1991-09-28T16:52:58 diff = 60 minutes
local date-time = 1991-09-28T17:52:58 diff = 0 minutes
local date-time = 1992-09-26T15:52:58 diff = 60 minutes
local date-time = 1992-09-26T16:52:58 diff = 0 minutes
local date-time = 1993-09-25T15:52:58 diff = 60 minutes
local date-time = 1993-09-25T16:52:58 diff = 0 minutes
local date-time = 1994-09-24T15:52:58 diff = 60 minutes
local date-time = 1994-09-24T16:52:58 diff = 0 minutes
local date-time = 1995-09-23T15:52:58 diff = 60 minutes
local date-time = 1995-09-23T16:52:58 diff = 0 minutes
local date-time = 1996-10-26T15:52:58 diff = 60 minutes
local date-time = 1996-10-26T16:52:58 diff = 0 minutes
local date-time = 1997-10-25T15:52:58 diff = 60 minutes
local date-time = 1997-10-25T16:52:58 diff = 0 minutes
local date-time = 1998-10-24T15:52:58 diff = 60 minutes
local date-time = 1998-10-24T16:52:58 diff = 0 minutes
local date-time = 1999-10-30T15:52:58 diff = 60 minutes
local date-time = 1999-10-30T16:52:58 diff = 0 minutes
local date-time = 2000-10-28T15:52:58 diff = 60 minutes
local date-time = 2000-10-28T16:52:58 diff = 0 minutes
local date-time = 2001-10-27T15:52:58 diff = 60 minutes
local date-time = 2001-10-27T16:52:58 diff = 0 minutes
local date-time = 2002-10-26T15:52:58 diff = 60 minutes
local date-time = 2002-10-26T16:52:58 diff = 0 minutes
local date-time = 2003-10-25T15:52:58 diff = 60 minutes
local date-time = 2003-10-25T16:52:58 diff = 0 minutes
local date-time = 2004-10-30T15:52:58 diff = 60 minutes
local date-time = 2004-10-30T16:52:58 diff = 0 minutes
local date-time = 2005-10-29T15:52:58 diff = 60 minutes
local date-time = 2005-10-29T16:52:58 diff = 0 minutes
local date-time = 2006-10-28T15:52:58 diff = 60 minutes
local date-time = 2006-10-28T16:52:58 diff = 0 minutes
local date-time = 2007-10-27T15:52:58 diff = 60 minutes
local date-time = 2007-10-27T16:52:58 diff = 0 minutes
local date-time = 2008-10-25T15:52:58 diff = 60 minutes
local date-time = 2008-10-25T16:52:58 diff = 0 minutes
local date-time = 2009-10-24T15:52:58 diff = 60 minutes
local date-time = 2009-10-24T16:52:58 diff = 0 minutes
local date-time = 2010-10-30T15:52:58 diff = 60 minutes
local date-time = 2010-10-30T16:52:58 diff = 0 minutes
local date-time = 2014-10-25T14:52:58 diff = 60 minutes
local date-time = 2014-10-25T15:52:58 diff = 0 minutes
counter = 91
{code}