Experiment with truncation of CPM values

cpm_truncate.c

#include <inttypes.h>
#include <stdio.h>

const double EXPECTED_CPM = 0.758630370209851;
const int TRUNCATE_LEN = 28;

int main(int argc, char **argv) {
  uint64_t cpm_i = *(uint64_t *)&EXPECTED_CPM;

  // Method 1: round up and truncate the lowest TRUNCATE_LEN bits.
  uint64_t cpm_i_trunc = ((cpm_i + (1 << TRUNCATE_LEN)) >> TRUNCATE_LEN) << TRUNCATE_LEN;
  double cpm = *(double *)&cpm_i_trunc;

  // Method 2 (most plausible): convert to 32-bit floating point (causes precision loss), then back to double.
  double cpm_f = (double)(float)EXPECTED_CPM;

  printf("%.16lf %.16lf %.16f (0x%lx)\n", EXPECTED_CPM, cpm, cpm_f, *(uint64_t *)&cpm_f);

  return 0;
}