[fortran,patch] Patch for PR 14394 - Precision of real type.

[Tianjiao Zhang]

Hi,

Excuse me that for pgf90 compiler,
pgf90 -r8 z.f gives the same result -255.9987041345172 for both real and
real*8.
Without the switch -r8,
real*8 gives -255.9958332631721

I used g77 and it gave -255.995833

I used gcc
#include <math.h>
int main(int argc,char **argv) {
long double a,b;
b= 1.5747025767L;
a=tan(b);
printf("%20.16Lf\n",a);
}
and it gave:
-255.9987041345172359

So we can use gcc to check the accuracy actually ?

Sincerely,
Tianjiao
-----------
Tianjiao Zhang wrote:

>SunOS 5.9 Generic_112233-08 sun4u sparc SUNW,Sun-Fire-880
>f77 WorkShop Compilers 4.2
>
>-255.99870413452
>
>On Linux 2.4.18-3smp #1i686 unknown
>pgf90 4.0-2
>-255.9958332631721
>
>
>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)
>>       PRINT*,AVS
>>       END
>> 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?
>>
>>
>>Feng Wang
>>
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