primesieve

primesieve is a command-line program and C/C++ library for quickly generating prime numbers. It is very cache efficient, it detects your CPU's L1 & L2 cache sizes and allocates its main data structures accordingly. It is also multi-threaded by default, it uses all available CPU cores whenever possible i.e. if sequential ordering is not required. primesieve can generate primes and prime k-tuplets up to 2⁶⁴.

primesieve generates primes using the segmented sieve of Eratosthenes with wheel factorization. This algorithm has a run time complexity of operations and uses memory. Furthermore primesieve uses the bucket sieve algorithm which improves the cache efficiency when generating primes > 2³². primesieve uses 8 bytes per sieving prime, hence its memory usage is about bytes per thread.

• More algorithm details

Installation

The primesieve command-line program can be installed using your operating system's package manager. For doing development with libprimesieve you may need to install libprimesieve-dev or libprimesieve-devel.

Usage examples

# Count the primes below 1e10 using all CPU cores
primesieve 1e10

# Print the primes below 1000000
primesieve 1000000 --print

# Print the twin primes below 1000000
primesieve 1000000 --print=2

# Count the prime triplets inside [1e10, 1e10+2^32]
primesieve 1e10 --dist=2^32 --count=3

Command-line options

Usage: primesieve [START] STOP [OPTION]...
Generate the primes and/or prime k-tuplets inside [START, STOP]
(< 2^64) using the segmented sieve of Eratosthenes.

Options:
  -c, --count[=NUM+]  Count primes and/or prime k-tuplets, NUM <= 6.
                      Count primes: -c or --count (default option),
                      count twin primes: -c2 or --count=2,
                      count prime triplets: -c3 or --count=3, ...
      --cpu-info      Print CPU information (cache sizes).
  -d, --dist=DIST     Sieve the interval [START, START + DIST].
  -h, --help          Print this help menu.
  -n, --nth-prime     Find the nth prime.
                      primesieve 100 -n: finds the 100th prime,
                      primesieve 2 100 -n: finds the 2nd prime > 100.
      --no-status     Turn off the progressing status.
  -p, --print[=NUM]   Print primes or prime k-tuplets, NUM <= 6.
                      Print primes: -p or --print,
                      print twin primes: -p2 or --print=2,
                      print prime triplets: -p3 or --print=3, ...
  -q, --quiet         Quiet mode, prints less output.
  -s, --size=SIZE     Set the sieve size in KiB, SIZE <= 4096.
                      By default primesieve uses a sieve size that
                      matches your CPU's L1 cache size or half of
                      your CPU's L2 cache size (per core).
      --test          Run various sieving tests.
  -t, --threads=NUM   Set the number of threads, NUM <= CPU cores.
                      Default setting: use all available CPU cores.
      --time          Print the time elapsed in seconds.
  -v, --version       Print version and license information.

Build instructions

You need to have installed a C++ compiler which supports C++11 (or later) and CMake ≥ 3.4.

cmake .
make -j
sudo make install

• Detailed build instructions

C++ API

Below is a C++ example with the most common libprimesieve use case.

#include <primesieve.hpp>
#include <iostream>

int main()
{
  primesieve::iterator it;
  uint64_t prime = it.next_prime();

  // Iterate over the primes below 10^6
  for (; prime < 1000000; prime = it.next_prime())
    std::cout << prime << std::endl;

  return 0;
}

• More C++ examples
• C++ API documentation

C API

libprimesieve's functions are exposed as C API via the primesieve.h header.

#include <primesieve.h>
#include <stdio.h>

int main()
{
  primesieve_iterator it;
  primesieve_init(&it);
  uint64_t prime;

  /* Iterate over the primes below 10^6 */
  while ((prime = primesieve_next_prime(&it)) < 1000000)
    printf("%llu\n", prime);

  primesieve_free_iterator(&it);
  return 0;
}

• More C examples
• C API documentation

libprimesieve performance tips

• primesieve::iterator::next_prime() runs up to 2x faster and uses only half as much memory as prev_prime(). Oftentimes algorithms that iterate over primes using prev_prime() can be rewritten using next_prime() which improves performance in most cases.

• primesieve::iterator is single-threaded. See the multi-threading section for how to parallelize an algorithm using multiple primesieve::iterator objects.

• The primesieve::iterator constructor and the primesieve::iterator::skipto() method take an optional stop_hint parameter that can provide a significant speedup if the sieving distance is relatively small e.g. < sqrt(start). If stop_hint is set primesieve::iterator will only buffer primes up to this limit.

• Many of libprimesieve's functions e.g. count_primes(start, stop) & nth_prime(n, start) incur an initialization overhead of O(sqrt(start)) even if the total sieving distance is tiny. It is therefore not a good idea to call these functions repeatedly in a loop unless the sieving distance is sufficiently large e.g. > sqrt(start). If the sieving distance is mostly small consider using a primesieve::iterator instead to avoid the recurring initialization overhead.

libprimesieve multi-threading

By default libprimesieve uses multi-threading for counting primes/k-tuplets and for finding the nth prime. However primesieve::iterator the most useful feature provided by libprimesieve runs single-threaded because it is simply not possible to efficiently parallelize the generation of primes in sequential order.

Hence if you want to parallelize an algorithm using primesieve::iterator you need to implement the multi-threading part yourself. The basic technique for parallelizing an algorithm using primesieve::iterator is:

• Subdivide the sieving distance into equally sized chunks.
• Process each chunk in its own thread.
• Combine the partial thread results to get the final result.

The C++ example below calculates the sum of the primes ≤ 10¹⁰ in parallel using OpenMP. Each thread processes a chunk of size (dist / threads) + 1 using its own primesieve::iterator object. The OpenMP reduction clause takes care of adding the partial prime sum results together in a thread safe manner.

#include <primesieve.hpp>
#include <iostream>
#include <omp.h>

int main()
{
  uint64_t sum = 0;
  uint64_t dist = 1e10;
  int threads = omp_get_max_threads();
  uint64_t thread_dist = (dist / threads) + 1;

  #pragma omp parallel for reduction(+: sum)
  for (int i = 0; i < threads; i++)
  {
    uint64_t start = i * thread_dist;
    uint64_t stop = std::min(start + thread_dist, dist);
    primesieve::iterator it(start, stop);
    uint64_t prime = it.next_prime();

    for (; prime <= stop; prime = it.next_prime())
      sum += prime;
  }

  std::cout << "Sum of the primes below " << dist << ": " << sum << std::endl;

  return 0;
}

# Unix-like OSes
wget https://primesieve.org/primesum.cpp
c++ -O3 -fopenmp primesum.cpp -o primesum -lprimesieve
time ./primesum

Linking against libprimesieve

Unix-like OSes

c++ -O2 primes.cpp -lprimesieve
cc  -O2 primes.c   -lprimesieve

If you have built primesieve yourself then the default installation path is /usr/local/lib which is not part of LD_LIBRARY_PATH on many OSes. Hence you may need to export some environment variables:

export LIBRARY_PATH=/usr/local/lib:$LIBRARY_PATH
export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH
export CPLUS_INCLUDE_PATH=/usr/local/include:$CPLUS_INCLUDE_PATH
export C_INCLUDE_PATH=/usr/local/include:$C_INCLUDE_PATH

Microsoft Visual C++

cl /O2 /EHsc primes.cpp /I primesieve\include /link primesieve.lib

CMake support

Since primesieve-6.4 you can easily link against libprimesieve in your CMakeLists.txt:

find_package(primesieve REQUIRED)
target_link_libraries(your_target primesieve::primesieve)

To link against the static libprimesieve use:

find_package(primesieve REQUIRED static)
target_link_libraries(your_target primesieve::primesieve)

Bindings for other languages

primesieve natively supports C and C++ and has bindings available for:

Many thanks to the developers of these bindings!