libtommath/bn_mp_get_long_long.c

#include <tommath.h>
#ifdef BN_MP_GET_LONG_LONG_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
 */

/* get the lower unsigned long long of an mp_int, platform dependent */
unsigned long long mp_get_long_long (mp_int * a)
{
  int i;
  unsigned long long res;

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

  /* get number of digits of the lsb we have to read */
  i = MIN(a->used,(int)((sizeof(unsigned long long)*CHAR_BIT+DIGIT_BIT-1)/DIGIT_BIT))-1;

  /* get most significant digit of result */
  res = DIGIT(a,i);

#if DIGIT_BIT < 64
  while (--i >= 0) {
    res = (res << DIGIT_BIT) | DIGIT(a,i);
  }
#endif
  return res;
}
#endif