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Re: Bug in 'fft'
>>>>> "Brian" == Brian Gough <bjg@network-theory.co.uk> writes:
Brian> Thanks for the bug report. The "n mod 7 = 0" behaviour isolates the
Brian> problem to c_pass7.c (the n=7 butterfly).
Brian> I think it may be a problem with gcc-2.95.1 compiling that file. The
Brian> code is working ok with other compilers. I don't know if you tried
Brian> compiling without -O, but if that makes the problem go away it would
Brian> support this hypothesis.
Brian> Perhaps someone on the list might know if there are potential problems
Brian> with that version of gcc.
First, sorry for not telling my compile flags.
They are: '-O2 -mpentium -malign-double'
And I use the stuff from the CVS repository, last update today
morning.
After changing from '-O2' to '-O' the problem goes away.
I tried the same procedure with the stuff in 'sum' but stil error
reports. Especially the test for
correct digits of asymptotic series
is independent of the optimizing level.
I also added 'gsl_ieee_env_setup ();' to the 'test.c' and played with
1) make check
2) GSL_IEEE_MODE="double-precision;round-to-nearest;" make check
To my surprise this switches the PASS/FAIL state of
1) PASS: correct digits for exp(10)
FAIL: correct digits for -log(2)
2) FAIL: correct digits for exp(10)
PASS: correct digits for -log(2)
Then I switched to 'ieee-utils':
I think there may be problems in the ieee-utils stuff for linux. The
example program from the docs about suming up works only if I use
GSL_IEEE_MODE="double-precision;round-to-nearest;"
the default mode 'extended-precision' does some 100 evaluations and
ends with a floating point exception and a core dump.
Some light about these problems are welcome, thanks.
Bye
Thomas
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Dipl. Phys. Thomas Walter
Inst. f. Physiklische Chemie II
Egerlandstr. 3 Tel.: ++9131-85 27326 / 27330
91058 Erlangen, Germany email: walter@pctc.chemie.uni-erlangen.de