### Re^3: a close prime number

 on Feb 14, 2005 at 19:01 UTC ( #430888=note: print w/replies, xml ) Need Help??

in reply to Re^2: a close prime number
in thread a close prime number

I wonder if it's quicker to add the digits of the number when you're checking to see if it's divisible by three and seeing if that resultant sum is divisible by three.

Replies are listed 'Best First'.
Re^4: a close prime number
by dragonchild (Archbishop) on Feb 14, 2005 at 19:11 UTC
It's not.
```use Benchmark qw( cmpthese );

my \$large_number = 3 * 1234647389;

cmpthese( -1, {
modulo => sub { \$large_number % 3 == 0 },
divide => sub { my \$v; \$v += \$_ for split //, \$large_number; \$v %
+3 == 0},
});

--------

Rate divide modulo
divide   30919/s     --   -99%
modulo 2120579/s  6759%     --

By a factor of 67 times faster. Or so ...

Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

Darn - so !(faster in my head == faster in code) :)

Thanks for the benchmarks, dragonchild.

Create A New User
Node Status?
node history
Node Type: note [id://430888]
help
Chatterbox?
and cookies bake in the oven...

How do I use this? | Other CB clients
Other Users?
Others wandering the Monastery: (2)
As of 2018-08-15 06:41 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
Asked to put a square peg in a round hole, I would:

Results (159 votes). Check out past polls.

Notices?