Visualising Redis' SCAN iteration

rev.cpp

#include <iostream>
#include <bitset>

static uint8_t rev(uint8_t v) {
    uint8_t s = 8 * sizeof(v); // bit size; must be power of 2
    uint8_t mask = ~0;
    while ((s >>= 1) > 0) {
        mask ^= (mask << s);
        v = ((v >> s) & mask) | ((v << s) & ~mask);
    }
    return v;
}

static void printval(std::ostream& io, char const * const label, const uint8_t val) {
  std::bitset<sizeof(uint8_t) * 8> binval(val);
  io << label << " = " << int(val) << " (" << binval << "), ";
}

int main() {
  // for (uint8_t i = 0; i < 100; ++i) {
  //   uint8_t revd = rev(i);
  //   uint8_t revincrd = revd + 1;
  //   uint8_t incrd = rev(revincrd);

  //   printval(std::cout, "i", i);
  //   printval(std::cout, "revd", revd);
  //   printval(std::cout, "revincrd", revincrd);
  //   printval(std::cout, "incrd", incrd);
  //   std::cout << std::endl;
  // }

  std::cout << std::endl;

  uint8_t val = 0;
  for (auto i = 0; i < 100; ++i) {
    printval(std::cout, "val", val);
    std::cout << std::endl;
    val = rev(val);
    ++val;
    val = rev(val);
  }
}