From: RandallBart Newsgroups: comp.software.year-2000 Subject: Unisys A Series Critical Dates (was: February 30, 2000 - NOT!) Date: Thu, 19 Mar 1998 23:31:44 -0800 John, I slightly mangled the story of the Unisys A Series date. I just saw a patch note for a coming A Series critical date, so I'll try to get it right this time: 1970-01-01 Day one of Unisys A Series timestamp 1987-01-01 Unisys A Series timestamp sets sign bit (bit 46) 2003-01-01 Unisys A Series timestamp sets unused bit (bit 47) 2036-01-01 Unisys A Series timestamp dies Notes: The use of this timestamp notation is already being phased out. I believe timestamps in the disk directory are now sixteen byte strings (CCYYMMDDhhmmsshh) The A Series numeric format is odd in several respects, the oddest being that the top bit is unused in normal numeric representation, and the sign bit is the second bit. The failure mode observed in 1987 involved moving a timestamp to an unsigned field, which caused the compiler to insert an absolute value instruction. The impending 2003 problem is because some numeric operations on some A Series platforms don't retain the unused bit. Most bit overflows happen at intervals of 16, 32, 64, and other powers of two. This bug surfaces when the timestamp reaches ages of 17, 33 and 66. Before I understood this I incorrectly stated before that the 1987 bug occurred in 1986. This time I RTFM to find out how exactly how this timestamp is stored. The A Series timestamp takes a Julian date in decimal, subtracts 1970, then stores that value in the top sixteen bits of the word. Thus: 1986-12-31 = 16365 = X"3FED" 1987-01-01 = 17000 = X"4268" Sign bit flipped 2002-12-31 = 32365 = X"7E6D" 2003-01-01 = 33000 = X"80E8" Unused bit flipped 2035-12-31 = 65365 = X"FF55" 2036-01-01 = 66000 = X"101D0" Overflow -- I |\ Randall Bart mailto:Barticus@usa.spam.net L |/ o |\ Barticus@worldnet.att.spam.net Barticus@hotmail.spam.com v | \ 1-310-542-6013 Please reply without spam e |\ Y |/ Panic in the Year Zero Zero: http://members.aol.com/PanicYr00 o |\ 33rd term revealed. Is it easy yet?: u |/ http://members.aol.com/PanicYr00/Sequence.html *** jrs@merlyn.demon.co.uk