mp_count_bits.c

   1 #include "tommath_private.h"
   2 #ifdef MP_COUNT_BITS_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 /* returns the number of bits in an int */
   7 int mp_count_bits(const mp_int *a)
   8 {
   9    int     r;
  10    mp_digit q;
  11
  12    /* shortcut */
  13    if (mp_iszero(a)) {
  14       return 0;
  15    }
  16
  17    /* get number of digits and add that */
  18    r = (a->used - 1) * MP_DIGIT_BIT;
  19
  20    /* take the last digit and count the bits in it */
  21    q = a->dp[a->used - 1];
  22    while (q > 0u) {
  23       ++r;
  24       q >>= 1u;
  25    }
  26    return r;
  27 }
  28 #endif