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<TITLE>CLHS: Issue TIME-ZONE-NON-INTEGER Writeup</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="../Issues/iss347_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss348.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss349_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue TIME-ZONE-NON-INTEGER Writeup</H2>
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<PRE><B>Status:</B> Passed v1 (as amended in v2) Mar-89 by 18-0 vote.<P>
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<B>Issue:</B> <A HREF="iss348.htm">TIME-ZONE-NON-INTEGER</A><P>
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<B>References:</B> Section 25.4.1 (Time Functions) (p. 443-444)<P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> 1-Mar-89, Version 1 by Chapman<P>
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10-Apr-89, Version 2 by Pitman (amendments per X3J13)<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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CLtL states that the time zone part of Decoded Time is an integer.<P>
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However, it is possible to have a non-integer time-zone.<P>
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<P>
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Proposal (<A HREF="iss348.htm">TIME-ZONE-NON-INTEGER:ALLOW</A>)<P>
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<P>
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Specify that the time zone part of Decoded Time is <P>
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1. a rational number (either an integer or a ratio)<P>
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2. in the range -24 to 24 (inclusive on both ends)<P>
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3. a multiple of 1/3600.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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1. For CL to accommodate all possible time designations, it is<P>
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necessary to allow time zone to be non-integer. Some places<P>
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in the world are on half-hour or quarter-hour times.<P>
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<P>
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There is no demand for floating point time zones. Since such<P>
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zones would introduce inexact arithmetic, we did not consider<P>
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adding them at this time.<P>
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<P>
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2. This prohibits the perverse use of very incredibly time zone<P>
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magnitudes to get around the year restriction on times<P>
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in portable code.<P>
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<P>
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3. This requires time zones to be represented as even multiples<P>
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of 1 second.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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VAX LISP allows time zone to be non-integer.<P>
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<P>
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<B>Cost to Implementors:<P>
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</B><P>
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Very slight. Implementations which use integer-only arithmetic<P>
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in dealing with time zones might have to switch to a more generic<P>
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kind of arithmetic.<P>
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<P>
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<B>Cost to Users:<P>
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</B><P>
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Depends on situation. Very slight negative to very strong positive<P>
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effects will be seen by users.<P>
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<P>
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In some cases, this legitimizes time zones which are already a<P>
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political necessity and may make life easier for users.<P>
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<P>
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In at least one known case, this will make things a little harder<P>
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because `very large' time zones will not be permitted. However, <P>
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such time zones probably were not really portable to begin with<P>
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so this is more just a recognition of the status quo.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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See Rationale.<P>
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<P>
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<B>Conversion Cost:<P>
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</B><P>
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In most cases, no user code will have to be modified.<P>
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<P>
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In the one known case using `very large' time zones, the user may<P>
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have to write his own time manipulation software if he really wants<P>
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to be portable.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Probably slightly improved.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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Haflich was claiming he might want to use very large negative time zones<P>
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to go back in history beyond 1900 (where universal times supposedly <P>
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bottom out). However, most implementations probably don't represent the<P>
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shifts in calendar system which occurred at various points before that<P>
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time, most implementors present at the Mar-89 meeting seemed to think this<P>
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`hack' was probably not really going to work portably anyway.<P>
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</PRE>
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