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From: Andrew Pinski <pinskia@physics.uc.edu> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: c++/7369: weird results with the statement "#define PI 4.*atan(1.)" Date: Sun, 21 Jul 2002 12:36:00 -0000 [thread overview] Message-ID: <20020721193601.29782.qmail@sources.redhat.com> (raw) The following reply was made to PR c++/7369; it has been noted by GNATS. From: Andrew Pinski <pinskia@physics.uc.edu> To: pel@ucla.edu Cc: gcc-gnats@gcc.gnu.org Subject: Re: c++/7369: weird results with the statement "#define PI 4.*atan(1.)" Date: Sun, 21 Jul 2002 15:26:53 -0400 No you have to use #define PI (4.0*atan(1.)) because if you don't the statement becomes 1/4.*atan(1.0) which is equal to .25*atan(1.0) not .25*1/atan(1.0). Please close this bug report the reported behavior is the correct one. Thanks, Andrew Pinski On Sunday, July 21, 2002, at 03:03 , pel@ucla.edu wrote: > >> Number: 7369 >> Category: c++ >> Synopsis: weird results with the statement "#define PI >> 4.*atan(1.)" >> Confidential: no >> Severity: non-critical >> Priority: low >> Responsible: unassigned >> State: open >> Class: sw-bug >> Submitter-Id: net >> Arrival-Date: Sun Jul 21 12:06:01 PDT 2002 >> Closed-Date: >> Last-Modified: >> Originator: Peter Latham >> Release: 2.96 >> Organization: >> Environment: > Red Hat Linux 7.3 >> Description: > If PI is defined via the statement > > #define PI 4.*atan(1.) > > then 1/PI and 1/3.14159 are different. >> How-To-Repeat: > compile using "g++ main.c". then type "a.out", which > prints PI, 1/PI and 1/3.14159. the result is > > 3.141593 0.196350 0.318310 > > If for some strange reasont the file didn't attach properly, > the source code is: > > > #include <stdio.h> > #include <math.h> > > #define PI 4.*atan(1.) > //#define PI 3.14159 > > void main(int argc, char** argv) > { > fprintf(stdout, "%f %f %f\n", PI, 1/PI, 1/3.14159); > } > > > > >> Fix: > the workaround is to not use atan in the define statement, > > #define PI=3.14159 > > this produces the correct output. > >> Release-Note: >> Audit-Trail: >> Unformatted: > ----gnatsweb-attachment---- > Content-Type: application/octet-stream; name="main.c" > Content-Transfer-Encoding: base64 > Content-Disposition: attachment; filename="main.c" > > CiNpbmNsdWRlIDxzdGRpby5oPgojaW5jbHVkZSA8bWF0aC5oPgoKI2RlZmluZSBQSSA0LiphdGFu > KDEuKQovLyNkZWZpbmUgUEkgMy4xNDE1OQoKdm9pZCBtYWluKGludCBhcmdjLCBjaGFyKiogYXJn > dikKewoJZnByaW50ZihzdGRvdXQsICIlZiAlZiAlZlxuIiwgUEksIDEvUEksIDEvMy4xNDE1OSk7 > Cn0K > >
next reply other threads:[~2002-07-21 19:36 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-07-21 12:36 Andrew Pinski [this message] -- strict thread matches above, loose matches on Subject: below -- 2002-07-21 12:46 gdr 2002-07-21 12:06 pel
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