Problem with zeros.

[Jerry DeLisle]

Tim Prince wrote:
> Tobias Burnus wrote:
>> Hi,
>>
>> Éric Depagne wrote:
>>  
>>> My code reads a file, and puts the content of this file into an array.
>>> The array is defined like this:
>>>
>>> DIMENSION X(40,30)
>>> The content of the file  looks like this:
>>> 9.999e-46 9.999e-46 9.999e-46 9.999e-46 9.999e-46 2.944E-19
>>>       
>> Which gives the run-time error:
>>
>> At line 2 of file xxx.f90 (unit = 5, file = 'stdin')
>> Fortran runtime error: Range error during floating point read
>>
>>  
>>> I would like to know if there is a way to let gfortran know that when 
>>> he encounters values that are too small, he shall convert them to zero ?
>>>       
>> To my knowledge not.
>>
>> I played around with other compiles and:
>>
>> a) 9.999e-46
>>
>>
>> 1. ifort, NAG f95, sunf95, pgf95: denormalized number: 1.4012985E-45
>> 2. g95, openf95: 0.0
>> 3. gfortran: Range error
>>
>> (gcc+glibc with scanf: (2).)
>>
>> b) 1e99
>>
>> 1. sunf95, g95, f95, openf95, pgf95: Inf
>> 2. ifort, gfortran: Range error
>>
>> (gcc+glibc with scanf: (1).)
>>
>> For (a) I think (1) is the best result and (2) is also ok. I don't see
>> any good reason to do (3).
>> For (b) one can argue whether (1) or (2) is better; I like (1) more, one
>> might argue that (2) has also its merits and one may argue for an
>> option, but overflow FP traps would have the same result, I'd guess.
>> (Assuming that the data is used later on.)
>>
>> What do the others think?
>>
>>   
> At the time when we persuaded the Intel compiler team to institute the 
> present behavior of ifort, the primary models for compatibility were g77 
> on linux, and CVF on Windows.  Both of those compilers silently convert 
> subnormal inputs to the nearest available sub-normal (0. if 
> appropriate).  Throwing an exception which terminates the program, in 
> the absence of iostat handling, breaks important applications.  So it 
> was accepted that the historical behavior of g77 and CVF should be 
> continued.
> 
Thanks for the information.  I am looking into why we do not get the sub-normals 
now.

Jerry