tomsfastmath/src/bit/fp_count_bits.c

/* TomsFastMath, a fast ISO C bignum library. -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
#include <tfm_private.h>

int fp_count_bits (fp_int * a)
{
  int     r;
  fp_digit q;

  /* shortcut */
  if (a->used == 0) {
    return 0;
  }

  /* get number of digits and add that */
  r = (a->used - 1) * DIGIT_BIT;

  /* take the last digit and count the bits in it */
  q = a->dp[a->used - 1];
  while (q > ((fp_digit) 0)) {
    ++r;
    q >>= ((fp_digit) 1);
  }
  return r;
}