The first numbers are quite easy to guess without reading any reference : - 400 years span 146097 days in gregorian calendar. - 100 years span 36524 days, except every 400 years. - 4 years span 1461 days, except every 100 years. - 1 year span 365 days, except every four years For months and days, the tricks are less trivial... Nicolas 2012/7/13 Sven Van Caekenberghe <sven@beta9.be>:
Yeah, but sometimes a clever algorithm comes from a book, so to speak.
Giving the variables long names, or the constants names, would not make that much difference, it would still be pretty hard to understand.
ZTimestamp class>>withJdn: jdn dayMonthYearDo: block "Return the value of executing block with the Gregorian Calender day, month and year as arguments, as computed from my Julian Day Number, jdn. See http://en.wikipedia.org/wiki/Julian_date#Gregorian_calendar_from_Julian_day_..."
| j g dg c dc b db a da y m d | j := jdn + 32044. g := j // 146097. dg := j \\ 146097. c := ((dg // 36524) + 1) * 3 // 4. dc := dg - (c * 36524). b := dc // 1461. db := dc \\ 1461. a := ((db // 365) + 1) * 3 // 4. da := db - (a * 365). y := (g * 400) + (c * 100) + (b * 4) + a. m := ((((da * 5) + 308)) // 153) - 2. d := da - ((m + 4) * 153 // 5) + 122. ^ block value: d + 1 value: ((m + 2) \\ 12) + 1 value: (y - 4800 + ((m * 2) // 12))
On 13 Jul 2012, at 17:53, Camillo Bruni wrote:
comments? decent variable names? no magic numbers? NOW you can find NONE of that in dayMonthYearDo!
================================================================== dayMonthYearDo: aBlock "Evaluation the block with three arguments: day month, year."
| l n i j dd mm yyyy | l := jdn + 68569. n := 4 * l // 146097. l := l - (146097 * n + 3 // 4). i := 4000 * (l + 1) // 1461001. l := l - (1461 * i // 4) + 31. j := 80 * l // 2447. dd := l - (2447 * j // 80). l := j // 11. mm := j + 2 - (12 * l). yyyy := 100 * (n - 49) + i + l.
^ aBlock value: dd value: mm value: yyyy.
==================================================================
so can anyone explain me the magic numbers here??