#1656: Bignum exponentiation yields wrong results
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Reporter: [EMAIL PROTECTED] | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.6
Severity: major | Keywords:
Difficulty: Unknown | Os: Linux
Testcase: | Architecture: x86_64 (amd64)
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I've used the following GHC program:
main = print $ 9^9^9
The result was right in the number of digits (approx. 350 millions) but
the last to digits are 94. By quick modular exponentiation, one finds out
that 9^9^9 mod 100 = 89. So the number is obviously wrong. Looking
further, at least the last 100 digits are wrong.
I have redone the calculation with demo/calc/calc.c included in the
distribution of the GNU gmp library. This yields a different number, that
could be correct ( 89, but I don't know if it is otherwise correct)
In both cases, the same libgmp3 shared object was used. But the GHC
version constantly used 8 GiB of memory and four hours just for outputting
the value in base 10, while the calculation of the value had been finished
in about 5 minutes. demo/calc/calc.c used about 30 minutes for the whole
job.
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1656>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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