jv@mh.nl (Johan Vromans) (11/16/90)
On DECsystem/Ultrix 4.0, perl 3.0 pl 41:
0+$] returns 3.0409999999999999 ...
Johan
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------------------------ "Arms are made for hugging" -------------------------urlichs@smurf.sub.org (Matthias Urlichs) (11/19/90)
In comp.lang.perl, article <1990Nov16.150010.7185@squirrel.mh.nl>,
Johan Vromans <jv@mh.nl> writes:
< On DECsystem/Ultrix 4.0, perl 3.0 pl 41:
<
< 0+$] returns 3.0409999999999999 ...
<
Same here (A/UX 2.0).
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Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de /(o\
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330) \o)/alanm@cognos.UUCP (Alan Myrvold) (11/20/90)
In article <1990Nov16.150010.7185@squirrel.mh.nl> Johan Vromans <jv@mh.nl> writes: >On DECsystem/Ultrix 4.0, perl 3.0 pl 41: > > 0+$] returns 3.0409999999999999 ... This nastiness is due to the discrepancy between : - the precision with which floating point numbers are converted to strings in perl's str.c (20 digits) and - the precision with which floating point numbers are stored on the system (usually ~15.9 decimal digits) The nastiness could be removed by changing str.c thusly : 183c183 < gcvt(str->str_u.str_nval,20,s); --- > gcvt(str->str_u.str_nval,15,s); 190c190 < (void)sprintf(s,"%.20g",str->str_u.str_nval); --- > (void)sprintf(s,"%.15g",str->str_u.str_nval); 16 digits would probably work for most constants, but it would be nice if print 49*(1/49),"\n"; displayed 1, and (on my system) this requires 15, not 16 digits to sprintf. Why the choice of 20 digits??? I dunno. 15 or 16 would make most sense for most floating point implementations. - Alan --- Alan Myrvold 3755 Riverside Dr. uunet!mitel!cunews!cognos!alanm Cognos Incorporated P.O. Box 9707 alanm@cognos.uucp (613) 738-1440 x5530 Ottawa, Ontario CANADA K1G 3Z4
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (11/20/90)
In article <&$7fg2.0&2@smurf.sub.org> urlichs@smurf.sub.org (Matthias Urlichs) writes: : In comp.lang.perl, article <1990Nov16.150010.7185@squirrel.mh.nl>, : Johan Vromans <jv@mh.nl> writes: : < On DECsystem/Ultrix 4.0, perl 3.0 pl 41: : < : < 0+$] returns 3.0409999999999999 ... : < : Same here (A/UX 2.0). This shouldn't surprise you, considering that 1/1000 is not exactly representable in base two. I thought about this when implementing it, and decided it was okay because $] >= 3.041 is still true. (This is because 3.041 is also represented internally as 3.0409999999...) If you want to print $] numerically, say printf("%5.3f",$]). Larry
tneff@bfmny0.BFM.COM (Tom Neff) (11/20/90)
Yeah but roundoff error in the VERSION NUMBER is bogus. Can't you force $] to have the string attribute and stay exactly "3.041"?
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (11/25/90)
In article <16047@bfmny0.BFM.COM> tneff@bfmny0.BFM.COM (Tom Neff) writes:
: Yeah but roundoff error in the VERSION NUMBER is bogus. Can't you force
: $] to have the string attribute and stay exactly "3.041"?
Not and stay compatible with what $] currently means in a string context.
Larryjv@mh.nl (Johan Vromans) (11/25/90)
In article <10523@jpl-devvax.JPL.NASA.GOV> lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) writes: In article <16047@bfmny0.BFM.COM> tneff@bfmny0.BFM.COM (Tom Neff) writes: : Yeah but roundoff error in the VERSION NUMBER is bogus. Can't you force : $] to have the string attribute and stay exactly "3.041"? Not and stay compatible with what $] currently means in a string context. I, who started this thread, can live with $version = sprintf("%.3f",$]). On the other hand, one could consider an array @] that contains the two integer values ($][$[] == 3 and $][1+$[] == 41), but I doubt if it is worth the trouble. Johan -- Johan Vromans jv@mh.nl via internet backbones Multihouse Automatisering bv uucp: ..!{uunet,hp4nl}!mh.nl!jv Doesburgweg 7, 2803 PL Gouda, The Netherlands phone/fax: +31 1820 62911/62500 ------------------------ "Arms are made for hugging" -------------------------