On Fri, 10 Jan 2014 21:35:25 -0700, Warner Losh wrote: > > On Jan 10, 2014, at 8:35 PM, Skip Newhall wrote: > >> 'Proscribe’ and 'prescribe' are distinct words: >> >> 'Proscribe' means to forbid, disallow, or prohibit. “School rules >> proscribe the use of pencils on exams.” >> >> 'Prescribe' means to lay out specifications or rules about >> something. "In the manner prescribed by law.” >> >> I don’t know the context of the sentence the Magnus refers to. > > Prescribe is the word I intended. POSIX mandates, requires, > prescribes that time is UTC.
No. While POSIX broken-down time resembles UTC, the underlying timescale (Seconds since the Epoch) is *not* UTC, in that every day contains exactly 60*60*24= 86,400 seconds. Leap seconds are *not* applied. The confusion arises because the POSIX Epoch is defined using UTC. But the progression rule is a form of TAI (with unknown but constant offset). POSIX background information follows. URL of index page: <http://pubs.opengroup.org/onlinepubs/009695399/> >From POSIX Base Definitions volume: 3.149 Epoch The time zero hours, zero minutes, zero seconds, on January 1, 1970 Coordinated Universal Time (UTC). >From the General Concepts volume: 4.14 Seconds Since the Epoch A value that approximates the number of seconds that have elapsed since the Epoch. A Coordinated Universal Time name (specified in terms of seconds (tm_sec), minutes (tm_min), hours (tm_hour), days since January 1 of the year (tm_yday), and calendar year minus 1900 (tm_year)) is related to a time represented as seconds since the Epoch, according to the expression below. If the year is <1970 or the value is negative, the relationship is undefined. If the year is >=1970 and the value is non-negative, the value is related to a Coordinated Universal Time name according to the C-language expression, where tm_sec, tm_min, tm_hour, tm_yday, and tm_year are all integer types: tm_sec + tm_min*60 + tm_hour*3600 + tm_yday*86400 + (tm_year-70)*31536000 + ((tm_year-69)/4)*86400 - ((tm_year-1)/100)*86400 + ((tm_year+299)/400)*86400 The relationship between the actual time of day and the current value for seconds since the Epoch is unspecified. How any changes to the value of seconds since the Epoch are made to align to a desired relationship with the current actual time is implementation-defined. As represented in seconds since the Epoch, each and every day shall be accounted for by exactly 86400 seconds. Note: The last three terms of the expression add in a day for each year that follows a leap year starting with the first leap year since the Epoch. The first term adds a day every 4 years starting in 1973, the second subtracts a day back out every 100 years starting in 2001, and the third adds a day back in every 400 years starting in 2001. The divisions in the formula are integer divisions; that is, the remainder is discarded leaving only the integer quotient. History: <http://en.wikipedia.org/wiki/Unix_time> Joe Gwinn _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
