id summary reporter owner description type status priority milestone component version resolution keywords cc os architecture failure testcase blockedby blocking related differential
1656 Bignum exponentiation yields wrong results rvb@… "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." bug closed normal 6.8.1 Compiler 6.6 worksforme Linux x86_64 (amd64)