[openfirmware] [commit] r2792 - ofw/fs
repository service
svn at openfirmware.info
Sat Dec 31 21:02:00 CET 2011
Author: wmb
Date: Sat Dec 31 21:01:59 2011
New Revision: 2792
URL: http://tracker.coreboot.org/trac/openfirmware/changeset/2792
Log:
OLPC trac #11563 - fixed longstanding problem with Unix timestamp conversion routines - leap year adjustment was badly broken.
Modified:
ofw/fs/unixtime.fth
Modified: ofw/fs/unixtime.fth
==============================================================================
--- ofw/fs/unixtime.fth Sat Dec 31 21:01:56 2011 (r2791)
+++ ofw/fs/unixtime.fth Sat Dec 31 21:01:59 2011 (r2792)
@@ -2,39 +2,112 @@
purpose: Convert Unix seconds to time and date
decimal
-\ date&time is number of seconds since 1970
+\ February is given 29 days so the loop in >d/m will exit at the "unloop".
+\ The array begins at March so that the leap day falls at the end.
create days/month
-\ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
- 31 c, 28 c, 31 c, 30 c, 31 c, 30 c, 31 c, 31 c, 30 c, 31 c, 30 c, 31 c,
+\ Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb
+ 31 c, 30 c, 31 c, 30 c, 31 c, 31 c, 30 c, 31 c, 30 c, 31 c, 31 c, 29 c,
-: >d/m ( day-in-year -- day month )
- 12 0 do
- days/month i ca+ c@ 2dup < if
- drop 1+ i 1+ leave
- then
- -
- loop
+\ In >d/m and d/m>, the yearly period starts on March 1. day-in-year is
+\ relative to March 1, and month-index 0 is March, 9 is December, 10 is January,
+\ 11 is February. This representation simplifies the calculations by
+\ putting the optional leap day at the end, i.e. day-of-year=365.
+
+\ Convert day-in-year to day-of-month and month-index.
+
+: >d/m ( day-in-year0..365 -- day1..31 month-index0..11 )
+ d# 12 0 do ( days-left )
+ days/month i ca+ c@ 2dup < if ( days-left )
+ drop 1+ i unloop exit ( -- day1..31 month-index0..11 )
+ then ( days-left )
+ - ( days-left' )
+ loop ( days-left )
+ \ This is reached only if the argument is >365
+ 1+ d# 12 ( day1..31 month-index0..11 )
;
-: unix-seconds> ( seconds -- s m h d m y )
- 60 u/mod 60 u/mod 24 u/mod ( s m h days )
- [ 365 4 * 1+ ] literal /mod >r ( s m h day-in-cycle ) ( r: cycles )
- dup [ 365 365 + 31 + 29 + ] literal
- 2dup = if \ exactly leap year Feb 29
- 3drop 2 29 2 ( s m h year-in-cycle d m )
- else
- > if 1- then \ after leap year
- 365 u/mod ( s m h day-in-year year-in-cycle )
- swap >d/m ( s m h year-in-cycle d m )
- then
- rot r> 4 * + 1970 + ( s m h d m y )
+
+\ Convert day-of-month and month-index to day-in-year.
+
+: d/m> ( day1..31 month-index0..11 -- day-in-year0..365 )
+ swap 1- swap 0 ?do i days/month + c@ + loop ( day-in-year )
;
-: >unix-seconds ( s m h d m y -- seconds ) \ since 1970
- d# 1970 - 4 /mod [ d# 365 4 * 1+ ] literal * ( s m h d m yrs days )
- swap d# 365 * + ( s m h d m days )
- swap 1 max d# 12 min ( s m h d days m' )
- 1- 0 ?do i days/month + c@ + loop ( s m h d days )
- + 1- ( s m h days )
- d# 24 * + d# 60 * + d# 60 * +
+
+\
+d# 365 constant d/y
+d/y d# 30 * \ Years from 1970 to 2000
+d# 7 + \ Leap days from 1970 to 2000
+d# 31 + \ Days in January 2000
+d# 28 + \ Days in February 2000 (not a leap year)
+constant days-to-break
+
+: unix-seconds> ( seconds -- s m h d m y )
+ \ Changing the 3 /mod's below to u/mod's would "fix" the year 2038 problem
+ \ at the expense of breaking dates before 1970.
+ d# 60 /mod d# 60 /mod d# 24 /mod ( s m h days )
+
+ \ Rotate the number space so that day 0 is March 1, 2000
+ \ That's convenient because it begins a 4 year + 1 day leap cycle
+ days-to-break -
+
+ \ Adjust days before day 0 for the fact that 2000, unlike other
+ \ 0mod4 years, is not a leap year
+ dup 0< if 1- then ( s m h days' )
+
+ \ Reduce modulo the number of days in a 4-year leap cycle
+ \ This depends on floored division
+ [ d/y 4 * 1+ ] literal /mod >r ( s m h day-in-cycle r: cycles )
+
+ \ Reduce by the number of days in a normal year
+ d/y /mod ( s m h day-in-year year-in-cycle r: cycles )
+
+ \ If year-in-cycle is 4, it's Feb 29
+ dup 4 = if ( s m h day-in-year year-in-cycle r: cycles )
+ \ Leap day Feb 29 at end of cycle
+ swap d/y + swap 1- ( s m h day-in-year' year-in-cycle' r: cycles )
+ then ( s m h day-in-year year-in-cycle r: cycles )
+ r> 4 * + >r ( s m h day-in-year r: year )
+
+ >d/m ( s m h day-in-month month-index r: year )
+
+ \ Adjust the month number - at this point March is 0 and we want it to be 3
+ 3 + ( s m h d month' r: year )
+
+ \ Months 13 and 14 are January and February of the following year
+ dup d# 13 >= if ( s m h d month r: year )
+ d# 12 - r> 1+ >r ( s m h d month' r: year' )
+ then ( s m h d month r: year )
+
+ r> d# 2000 + ( s m h d m y )
+;
+
+: >unix-seconds ( s m h d m y -- seconds ) \ since 1970
+ d# 2000 - >r ( s m h d m r: y' )
+
+ \ Move January and February to the end so the leap day is day number 365
+ dup 3 < if ( s m h d month' r: y )
+ d# 12 + r> 1- >r ( s m h d month' r: y' )
+ then ( s m h d month r: y )
+
+ \ Convert month numbers 3..14 to 0..11
+ 3 - ( s m h d month-index r: y )
+
+ \ Convert day and month to day in year
+ d/m> ( s m h day-in-year r: y )
+
+ r@ 4 / ( s m h day-in-year leap-years r: y )
+ r> d/y * + ( s m h day-in-year year-days )
+ + ( s m h days )
+
+ \ Adjust for the missing leap day in 2000
+ dup 0< if 1+ then ( s m h days' )
+
+ \ Adjust to 1970
+ days-to-break + ( s m h days' )
+
+
+ \ Changing the 3 *'s below to u*'s would "fix" the year 2038 problem
+ \ at the expense of breaking dates before 1970.
+ d# 24 * + d# 60 * + d# 60 * + ( seconds )
;
\ e.g. time&date >unix-seconds
More information about the openfirmware
mailing list