CODEWITHSUNDEEP
fortrangfortranfloating-point-exceptions
user2417662
user2417662

Reputation: 47

floating point error gfortran

I am trying to debug a Fortran program. To catch floating point errors, I'm using the following compiler options for gfortran 4.9.0:

FFLAGS1 = -std=f2003 -ffree-form -fdefault-real-8 -fdefault-double-8  \
          -Ofast -fall-intrinsics -fcheck=all -m64 \
          -fno-trapping-math -c \
          -ffpe-trap=invalid,zero,overflow,underflow,precision,denormal -Wall

With these options, the program fails at this line:

read(ctrlUnit,*) slope_fasst, aspect

when trying to read these inputs: 10.0 70.0

If I remove 

-ffpe-trap=invalid,zero,overflow,underflow,precision,denormal

from the compiler options, it reads the following line just fine. Both variables are declared as real(8). In the input file, I've tried spaces, commas, etc. but see no changes. Does anyone have a suggestion?

Upvotes: 0

Views: 6174

Answers (1)

agentp
agentp

Reputation: 6999

It seems the gfortran -ffpe-trap,precision flag results in errors for perfectly normal / routine read/write operations.

For example, this program throws a "Floating exception" error:

    write(*,*)1.0
    end

(gfortran 4.1.2, redhat linux)

Solution, do not use that flag.

Note this makes sense since the conversion from machine number to/from ascii results in a loss of precision ( I'm not sure if thats the intent of the flag to catch such though )

Upvotes: 1

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