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From: "sgk at troutmask dot apl.washington.edu" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/57871] gfortran -freal-4-real-16 gives wrong result for selected_real_kind(1) Date: Wed, 10 Jul 2013 20:02:00 -0000 [thread overview] Message-ID: <bug-57871-4-xZfHkcAb7l@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-57871-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57871 --- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> --- On Wed, Jul 10, 2013 at 05:42:03PM +0000, kargl at gcc dot gnu.org wrote: > implicit none > integer,parameter:: p1 = selected_real_kind(1) > > This initialization expression is requesting the type with > smallest precision that exceeds 1. With -freal-4-real-16, > that type is double precision (ie kind=8). The problem > lies in gfc_simplify_selected_real_kind. It has no knowledge > of the -freal-*-real-* options. The loop (lines 5447-5457) (remove loop code) > searchs the ordered set [24, 53, 53, 113] (on FreeBSD-i386) or > [24, 53, 64, 113] (on FreeBSD-amd64). In either case, the > initialization expression returns REAL(4). However, with > -freal-4-real-16, one might expect the ordered set to be > searched is [113, 53, 64, 113] as REAL(4) has been promoted > to REAL(16). The results of running John's code are odder than what one might expect. The normal results: % gfc4x -o foo foo.f90 && ./foo kind(1.0_p1) 4 precision(1.0_p1) 6 kind(1.0_dp) 8 precision(1.0_dp) 15 One might expect the first line to be 8 and 15, respectively. % gfc4x -o foo foo.f90 -freal-4-real-16 && ./foo kind(1.0_p1) 16 precision(1.0_p1) 33 kind(1.0_dp) 8 precision(1.0_dp) 15 Here the default real kind is promoted to REAL(8), but literal constants declared with a kind type suffix are not promoted. The first line is the correct output, although one might anticipate 8 and 15. But, what may be surprising is that the double precision kind has been bumped to quad precision. troutmask:sgk[207] gfc4x -o foo foo.f90 -fdefault-real-8 && ./foo kind(1.0_p1) 4 precision(1.0_p1) 6 kind(1.0_dp) 16 precision(1.0_dp) 33 I've always hated these type options as a lzy programmer's crutch who refuses to properly port an algorithm from one precision to another.
next prev parent reply other threads:[~2013-07-10 20:02 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-07-09 23:38 [Bug fortran/57871] New: " john.harper at vuw dot ac.nz 2013-07-10 13:07 ` [Bug fortran/57871] " dominiq at lps dot ens.fr 2013-07-10 17:42 ` kargl at gcc dot gnu.org 2013-07-10 20:02 ` sgk at troutmask dot apl.washington.edu [this message] 2013-07-10 21:31 ` harper at msor dot vuw.ac.nz 2013-07-11 22:30 ` harper at msor dot vuw.ac.nz 2013-07-11 22:51 ` sgk at troutmask dot apl.washington.edu 2013-11-25 0:59 ` kargl at gcc dot gnu.org 2021-03-04 11:59 ` dominiq at lps dot ens.fr 2021-03-05 9:43 ` cvs-commit at gcc dot gnu.org 2021-03-05 9:53 ` burnus at gcc dot gnu.org 2021-03-07 13:19 ` dominiq at lps dot ens.fr
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