Re: machar and ifort


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Posted by Michal Tarana on June 11, 2007 at 13:13:44:

In Reply to: Re: machar and ifort posted by Valera on June 11, 2007 at 12:36:52:

Hello,
^^^^^^

thank you for your answer.

: if you have a look at src/util/machar.f you will find out that for some platforms these numbers are hardcoded, but for others - are computed..

: And I can give a simple explanation - why (sometimes) it is impossible to use "standard" way of computing machine dependent constants.
: Let's look at the simple statement:
: IF(eps+1.gt.1)
: A very 'smart' compiler (with -O2) can simplify the condition to
: IF(eps.gt.0)

: So. The only way to avoid this problem is to hardcode these constants..
Hmmm...this is, what I somewhat have found in the meantime. Could you, please, suggest me some way how to determine the constants that should be hardwired into machar, please? I mean...I expected that the same optimalization (-O2) gives the same results in 64-bit machine as in the 32-bit case. If the only way of solution is to hardcode the constants into the code, are the correct values known?

Thank you for the answer.
Michal



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