compiling c++ programs with NTL library

[Jakiro]

Hi, does anyone know how to compile c++ programs that uses the NTL library( http://www.shoup.net/ntl )?

I have installed the package ntl-devel by using yum.
Now I have a simple c++ program that uses NTL:

#include <NTL/ZZ.h>

NTL_CLIENT

int main()
{
   ZZ a, b, c; 

   cin >> a; 
   cin >> b; 
   c = (a+1)*(b+1);
   cout << c << "\n";

   return 0
}

How do I compile this program with g++?
The usual

g++ example.cpp -o example

does not work.

[markkuk]

Install the gmp-devel package and link with both ntl and gmp libraries:

g++ example.cpp -o example -lntl -lgmp

You must also fix the example code by adding the missing "#include <iostream>" and "using namespace std;" statements.

[Jakiro]

Now it works. Thanks a lot.

[bron1]

Actually, only two things were needed.

(1) The last line of c++ code needs a semicolon, i.e.

return 0;

(2) The g++ call needs only the -lntl flag, i.e.

g++ example.cpp -o example -lntl

(assuming NTL is was installed to default location which is usually /usr/local).

The usual #include statement and namespace statement mentioned by markkuk are not necessary nor is the -lgmp flag for g++ unless NTL was compiled with GMP. However, including all these does not hurt.

[RupertPupkin]

Originally Posted by bron1

assuming NTL is was installed to default location which is usually /usr/local

Fedora packages never install under /usr/local. For example, the 64-bit Fedora 17 ntl and ntl-devel packages put the libraries and headers in /usr/lib64 and /usr/include, respectively. You are correct that only "g++ example.cpp -o example -lntl" is needed to compile that code, as long as you install the ntl/ntl-devel packages via yum.

On a side note, I never knew about NTL until now, glad to learn about it. For arbitrary-length integer computations I'm curious to see how it compares to GMP, performance-wise. There's a thread here about using GMP to compute the 46th Mersenne prime. Maybe I'll try to do the same with NTL, though it appears that NTL was compiled with GMP!

$ ldd /usr/lib64/libntl.so.0.1.0
        linux-vdso.so.1 =>  (0x00007fffcc267000)
        libgmp.so.10 => /lib64/libgmp.so.10 (0x00007f55dfedb000)
        libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f55dfbd7000)
        libm.so.6 => /lib64/libm.so.6 (0x00007f55df8dc000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f55df525000)
        libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f55df30f000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f55e0541000)

[RupertPupkin]

Well it looks like NTL is nowhere near as fast as GMP. I used this code (mersenneNTL.cpp)

#include <NTL/ZZ.h>

NTL_CLIENT

int main(int argc, char *argv[]) {
   char *endptr;
   unsigned long int a = strtoul(argv[1],&endptr,10);
   ZZ b = power2_ZZ(a) - 1;
   cout << b;
   return 0;
}

and compiled and ran it like this

$ g++ -o mersenneNTL mersenneNTL.cpp -lntl
$ time ./mersenneNTL 43112609 > M46

to compute the 46th Mersenne prime (2^43112609 - 1). After 21 minutes (with my cpu heating up to 140F) and still not finished I finally had to kill it. With GMP it takes about 6 seconds to finish. I tried removing the last digit (so that it'd compute 2^4311260 - 1), and the NTL version did finish in about 17 seconds, whereas the GMP version did it in less than a second.

I think the bottleneck with NTL might be the cout statement. GMP has a specialized printf function called gmp_printf that recognizes the large integer type, but for NTL I couldn't find an equivalent so I stuck with cout.