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Unwanted compiler optimization (was: Bug report and fix for adaptive step size control in ODE solving)


Dear Optimization specialists,

On 02.01.2008, at 19:46, Frank Reininghaus wrote:

Jochen Küpper wrote:

However, why don't you test what you really describe your comment? This would look like the following (untested):

h0 = GSL_MAX_DBL(GSL_DBL_MIN, (t0 != t0+h0) ? h0 : GSL_DBL_EPSILON*t0);

Actually, I had been thinking of something like that first, but then I was afraid that an optimising compiler might transform 't0 != t0+h0' into '0 != h0', making the patch useless for the 'h0 < GSL_DBL_EPSILON*t0' problem.


Is this an optimization that is considered valid even for floating- point calculations in compiler building?

Maybe we should ask our friends from the GCC development about it...

Greetings,
Jochen
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