Bignum exponentiation yields wrong results
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.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.6 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |