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Re: [fortran,patch] Patch for PR 14394 - Precision of real type.
- From: Paul Brook <paul at codesourcery dot com>
- To: fortran at gcc dot gnu dot org
- Cc: Feng Wang <wf_cs at yahoo dot com>, patch <gcc-patches at gcc dot gnu dot org>,stevenb at suse dot de
- Date: Wed, 24 Mar 2004 11:36:37 +0000
- Subject: Re: [fortran,patch] Patch for PR 14394 - Precision of real type.
- Organization: CodeSourcery
- References: <firstname.lastname@example.org>
On Wednesday 10 March 2004 04:34, Feng Wang wrote:
> Hi, all
> This patch fix PR 14394. Reported by Bud. Test case:
> cat z.f
> REAL AVS,BVS
> BVS = 1.5747025767
> AVS = TAN(BVS)
> There is one problem converting the real type from mpf to gcc tree. With
> -fdump-parse-tree we can see fortran gets the input and parse correctly.
> gfc_conv_mpf_to_tree in trans-const.c use string as the intermediate of the
> conversion. As convert mpf to string, we specify the maximum digits number
> of the real value. In my patch, I loosen the limit.
> I tested real and real*8 type with the patch. The real type got the same
> result with Intel's compiler. But with real*8 type, gfortran gave the
> result: -255.998704134517, compared with Intel's -255.995833263172. The
> difference of them is above 0.002. With calculator I comfirmed the
> gfortran's result should be correct. But can anyone give more comparation
> with other compilers. What's your opinion?
Ok, although it needs a changelog entry.
I suspect some compilers/libraries use faster, less accurate math routines by
default. This may explain the differences you are seeing.