int32 vs int64, C++ (gcc)

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#include <iostream>
#include <chrono>
#include <cstring>

using namespace std::chrono;

template<typename T>
void runTest(const char* msg, void* buf, size_t len)
{
  const size_t n = len / sizeof(T);
  T* data = reinterpret_cast<T*>(buf);
  T seed = 1234567;
  milliseconds tmstart = duration_cast<milliseconds>(system_clock::now().time_since_epoch());
  for (size_t i = 0; i < n; i++) {
    const size_t ofst = i;
    seed = data[ofst] = (seed << 6) ^ (seed >> 2) + (T)i - (ofst ? data[ofst - 1] : seed);
    if (ofst > 4) {
      T a = data[ofst - 1];
      T b = data[ofst - 2];
      T c = data[ofst - 3];
      T d = data[ofst - 4];
      d *= ++a;
      c *= --b;
      a *= b ^ c--;
      d = a - 8;
      a += 8;
      data[ofst] ^= a;
      a += c ^ d;
      data[ofst] += a;
    }
  }
  milliseconds tmend = duration_cast<milliseconds>(system_clock::now().time_since_epoch());
  std::cout << msg << ": " << (tmend - tmstart).count() << " ms\n";
}

int main()
{
  const size_t len = 100 * 1000 * 1000;
  std::cout << sizeof(size_t) * 8 << "-bit mode\n";
  uint8_t* buf = new uint8_t[len];
  memset(buf, 2, len);
  runTest<int64_t>("int64", buf, len);
  memset(buf, 2, len);
  runTest<int32_t>("int32", buf, len);
  delete buf;
}

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Compilation time: 0.42 sec, absolute running time: 0.34 sec, cpu time: 0.27 sec, memory peak: 96 Mb, absolute service time: 0,78 sec