Otto Moerbeek <o...@drijf.net> writes:
> On Sun, Nov 03, 2024 at 08:13:20AM +0100, Otto Moerbeek wrote:
>
>> On Sun, Nov 03, 2024 at 09:38:47AM +0700, hahahahacker2009 wrote:
>>
>> > Hello,
>> > OpenBSD bc(1) is unable to calculate very big number,
>> > for example, (1024*1024)^(1024*1024) run for an hour and still cannot
>> > give me the result.
>> > It just use about 11M of memory and 100% CPU.
>> > Gavin Howard's bc port do it in 2 minutes
>> > GNU bc on Linux do it in 5 minutes.
>>
>> bc uses dc which does a simple exponentation computation, which is
>> basically doing repeated multiplications. I'm sure there are smarter
>> methods, it's not just implemented that way.
>
> Oh, I looked and I did it a bit smarter when I wrote that code 20
> years back, but still, I think it can be improved.
>
The problem seems more on numnber printing than on number exponentation.
$ /usr/bin/time -lp dc -e '1024 1024 * 1024 1024 * ^'
real 46.39
user 45.66
sys 0.00
15244 maximum resident set size
0 average shared memory size
0 average unshared data size
0 average unshared stack size
3509 minor page faults
1 major page faults
0 swaps
0 block input operations
0 block output operations
0 messages sent
0 messages received
0 signals received
0 voluntary context switches
3334 involuntary context switches
The exponentation took ~50 seconds (dc(1) doesn't print the number on
the stack by default).
--
Sebastien Marie
