Home-baked random number generator.

randym.cpp

// clear && gcc -std=c++17 -pthread -O2 randym.cpp && time ./a.out

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/time.h>

using u64 = unsigned long long int;

static volatile int bit = 600'000;

void* peek(void* data) {
  printf("peek()\n");
  const int target_len = 32;
  int result[target_len] = {};
  for (int i = 0; i < target_len; ++i) {
    usleep(1000);
    result[i] = bit;
  }
  unsigned int n = 0;
  for (int i = 0; i < target_len; ++i) {
    if (result[i] == 1)
      n = n ^ (1 << i);
  }
  printf("\nRandom number: %d\n", n);
  exit(0);
  return NULL;
}

static volatile int flipping = 0;

void* flip(void* data) {
  printf("flip()\n");
  flipping = 1;
  while (1) {
    // bit ^= 1;
    bit = bit == 600'000 ? 800'000 : 600'000;
  }
}

void peeks_stat_test() {
  while (!flipping);
  printf("peeks_stat_test()\n");
  u64 ones = 0;
  u64 zeros = 0;
  u64 limit = 100'000'000;
  for (u64 i = 0; i < limit; ++i) {
    usleep(10);
    if (bit == 600'000) ones++;
    else zeros++;
    if (i % 500'000 == 0 && i != 0) {
      double sum = (double) ones + zeros;
      int diff = abs((float) (int) ones - zeros);
      printf("  Ones: %llu (%f%%)\n", ones, ones * 100.0 / sum);
      printf("  Zeros: %llu (%f%%)\n", zeros, zeros * 100.0 / sum);
      printf("  Diff: %d (%f%%)\n", diff, diff * 100.0 / sum);
      printf("  ---\n");
    }
  }
  double sum = (double) ones + zeros;
  int diff = (int) ones - zeros;
  printf("  Ones: %llu (%f%%)\n", ones, ones * 100.0 / sum);
  printf("  Zeros: %llu (%f%%)\n", zeros, zeros * 100.0 / sum);
  printf("  Diff: %d (%f%%)\n", diff, diff * 100.0 / sum);
}

double timeval_diff(const timeval& t1, const timeval& t2) {
  double t = (t2.tv_sec - t1.tv_sec) * 1000.0;
  t += (t2.tv_usec - t1.tv_usec) / 1000.0;
  return t;
}

void flips_per_ms_test() {
  printf("flips_per_ms_test()\n");

  u64 limit = 100'000'000;
  volatile int testBit = 0;
  struct timeval t1, t2, t3, t4, t5;

  gettimeofday(&t1, NULL);
  for (u64 i = 0; i < limit; ++i) testBit ^= 1;
  gettimeofday(&t2, NULL);
  for (u64 i = 0; i < limit; ++i) testBit = !testBit;
  gettimeofday(&t3, NULL);
  for (u64 i = 0; i < limit; ++i) testBit = testBit == 0 ? 1 : 0;
  gettimeofday(&t4, NULL);
  for (u64 i = 0; i < limit; ++i) testBit = testBit == 1 ? 0 : 1;
  gettimeofday(&t5, NULL);

  double xor_t = timeval_diff(t1, t2);
  double not_t = timeval_diff(t2, t3);
  double zero_t = timeval_diff(t3, t4);
  double one_t = timeval_diff(t4, t5);

  printf("  `bit ^ 1`: %f ms (%f ops/ms)\n", xor_t, limit / xor_t);
  printf("  `!bit`: %f ms (%f ops/ms)\n", not_t, limit / not_t);
  printf("  `bit == 0`: %f ms (%f ops/ms)\n", zero_t, limit / zero_t);
  printf("  `bit == 1`: %f ms (%f ops/ms)\n", one_t, limit / one_t);
}

int main() {
  flips_per_ms_test();
  
  pthread_t fliper;
  pthread_create(&fliper, NULL, flip, NULL);
  
  peeks_stat_test();

  pthread_t peeker;
  pthread_create(&peeker, NULL, peek, NULL);
  pthread_join(peeker, NULL);

  return 0;
}