// based on a couple of StackOverflow answers
#include <QCoreApplication>

#include <QtDebug>

qint32 sign_extend_24_32(qint32 x) {
  const int bits = 24;
  qint32 m = 1u << (bits - 1);
  return (x ^ m) - m;
}

int main(int argc, char *argv[]) {
  QCoreApplication a(argc, argv);

  qint32 i = 262000;

  qint32 j = i & 0xFFFFFF;

  qint32 k = sign_extend_24_32(j);

  qDebug() << i << j << k;

  return a.exec();
}