Performance comparison pr0crustes/BigNumber vs GMP

/*
  Speed comparison of a BigNumber class vs GMP
  https://github.com/pr0crustes/BigNumber

  g++ -O3 -Wall -Wno-sign-compare -Iinclude mult_speed.cc -lgmpxx -lgmp -o mult_speed

           Time to multiply two N-digit numbers, in seconds
                   1000      2000  10000000 20000000
    BigNumber      2.19      15.1
    GMP        .0000223  .0000268       .33      .67
*/
#include <iostream>
#include <string>
#include <random>
#include <chrono>
#include <cstdlib>
#include <gmpxx.h>
#include "BigNumber.h"

typedef std::chrono::high_resolution_clock::time_point TimeType;

std::random_device rand_dev;
std::default_random_engine rand_engine(rand_dev());
std::uniform_int_distribution<int> rand_int_0_9(0, 9), rand_int_1_9(1, 9);

TimeType now() {
  return std::chrono::high_resolution_clock::now();
}

double timeDiff(const TimeType &start_time, const TimeType &end_time) {
  typedef std::chrono::duration<double> seconds_type;
  return std::chrono::duration_cast<seconds_type>(end_time - start_time)
    .count();
}

void randomFill(std::string &s) {
  if (s.length() == 0) return;
  s[0] = '0' + rand_int_1_9(rand_engine);
  for (size_t i=1; i < s.length(); i++)
    s[i] = '0' + rand_int_0_9(rand_engine);
}


void testBigNumber(const std::string &in_str1, const std::string &in_str2) {
  TimeType start_time;

  std::cout << "Convert to BigNumber..." << std::flush;
  start_time = now();
  BigNumber bignum_in1(in_str1), bignum_in2(in_str2);
  std::cout << "done (" << timeDiff(start_time, now()) << "s)\n" << std::flush;

  BigNumber bignum_out;

  std::cout << "Multiplying BigNumber..." << std::flush;
  start_time = now();
  bignum_out = bignum_in1 * bignum_in2;
  std::cout << "done (" << timeDiff(start_time, now()) << "s)\n" << std::flush;

  // std::cout << bignum_out << std::endl;

  // make sure the multiplication isn't optimized out
  if (bignum_out.isZero()) std::cout << "(shouldn't output)\n";

  std::cout << std::endl;
}


void testGMP(const std::string &in_str1, const std::string &in_str2) {
  TimeType start_time;

  std::cout << "Converting to mpz_class..." << std::flush;
  start_time = now();
  mpz_class gmp_in1(in_str1), gmp_in2(in_str2);
  std::cout << "done (" << timeDiff(start_time, now()) << "s)\n" << std::flush;
  // std::cout << gmp_in1 << std::endl;
  // std::cout << gmp_in2 << std::endl;

  std::cout << "Multiplying mpz_class..." << std::flush;
  mpz_class gmp_out;
  start_time = now();
  gmp_out = gmp_in1 * gmp_in2;

  std::cout << "done (" << timeDiff(start_time, now()) << "s)\n" << std::flush;

  // std::cout << gmp_out << std::endl;

  // make sure the multiplication isn't optimized out
  if (sgn(gmp_out) == -1) std::cout << "(shouldn't output)\n";

  std::cout << std::endl;
}


int main(int argc, char **argv) {
  TimeType start_time;
  int length = 10;

  if (argc == 1) {
    std::cout << "\n  mult_speed <length>\n"
              << "  Time BigNumber and GMP multiply two integers of <length> digits.\n\n";
    return 0;
  } else {
    length = atoi(argv[1]);
    if (length <= 0) {
      std::cout << "Length must be positive.\n";
      return 1;
    }
  }

  std::cout << "Length=" << length << std::endl;

  std::string in_str1(length, '0'), in_str2(length, '0');
  std::cout << "Creating random inputs..." << std::flush;
  start_time = now();
  randomFill(in_str1);
  randomFill(in_str2);
  std::cout << "done (" << timeDiff(start_time, now()) << "s)\n" << std::flush;
  // std::cout << in_str1 << std::endl;
  // std::cout << in_str2 << std::endl;

  std::cout << std::endl;

  testBigNumber(in_str1, in_str2);
  testGMP(in_str1, in_str2);

  return 0;
}