Bignum doesn't work.....?

Ruby
1

Forgive me if this has been answered, I have look all around and can’t
seem
to find an answer. I am trying to implement the Fermat primality test (
Fermat primality test - Wikipedia ) in Ruby. The
problem is
everytime ruby does the a^(n-1) computation, it seems to stumble on
numbers
like 1000 (so its doing a^999). I have set both a and n to fixnums, and
according to everything I have read, it should switch to bignum if the
result is too big. But it doesn’t seem to do that, it just seems to spit
out
infinity. Any ideas? I used the latest one click installer to install
Ruby.

Ethan

2

It sounds like either the base or the exponent you are using (or both)
are floats.

The following demonstrates this fairly well:

irb(main):012:0> 4.0999
=> Infinity
irb(main):013:0> 4999.0
=> Infinity
irb(main):014:0> 4**999
=>
28703267381856363105820830029442049600557942552217380011941068420644156534809
25784641648715791265674796114911597468656933617797402157638328564828390416632963
47824972863280700001721947870600112178572317475158715611954038659115970909868292
56510116588492726249139540599702236157401405827912384041055492583170336042227246
11462640059487120197851472523369412510725067917665645763050203305907032294031697
08293016497488491045317554449646010105399632958128852223584755229801387394458974
18009790020489304157645688845106395931503882087196604858013627228818945970656293
858882200205710692704491363440546212787257344

–
Marcel