fast alternative to the modulo reduction (code sample)

fastaltmod.c

#include <iostream>
#include <cstdint>

using namespace std;


// we are going to generate random numbers using 
// an xorshift generator

static uint32_t xorshift_y;

void xorshift32_seed(uint32_t seed) { xorshift_y = seed;}


uint32_t xorshift32(void) {
  xorshift_y ^= (xorshift_y << 13);
  xorshift_y ^= (xorshift_y >> 17);
  return xorshift_y ^= (xorshift_y << 5);
}


uint32_t reduce(uint32_t x, uint32_t N)  {
    return (((uint64_t)x * (uint64_t)N) >> 32);
}

int main() {
    // seeding the rng
    xorshift32_seed(1234);
    // we print 10 numbers
    for(int k = 0; k < 10; k++)
      cout<< reduce(xorshift32(), 7) << endl;
    return 0;
}