/*
 * Copyright (C) 2022, Andrei Egorov
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
uint8_t __attribute__ ((noinline)) NumOneBits(uint8_t b) {
  uint8_t result;
  asm volatile(
    "mov r18,%1\n\t"
    "clr %0\n\t"
    "tst r18\n\t"
    "l:\n\t"
    "breq exit\n\t"
    "inc %0\n\t"
    "mov r19,r18\n\t"
    "dec r19\n\t"
    "and r18,r19\n\t"
    "rjmp l\n\t"
    "exit:\n\t"
    : "=r" (result)
    : "r" (b)
    : "r18", "r19"
  );
  return result;
}

void setup() {
  Serial.begin(115200);
}

void loop() {
  static byte i(0);
  Serial.print(NumOneBits(i));
  Serial.print(" ");
  if (!(++i%16)) Serial.println();
  if (!i) while (1);
}