/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/**
   @file ocb_ntz.c
   OCB implementation, internal function, by Tom St Denis
*/

#include "tomcrypt_private.h"

#ifdef LTC_OCB_MODE

/**
   Returns the number of leading zero bits [from lsb up]
   @param x  The 32-bit value to observe
   @return   The number of bits [from the lsb up] that are zero
*/
int ocb_ntz(unsigned long x)
{
#if defined(LTC_HAVE_CTZL_BUILTIN)
   if (x == 0)
      return sizeof(unsigned long) * CHAR_BIT;
   return __builtin_ctzl(x);
#else
   int c;
   x &= 0xFFFFFFFFUL;
   c = 0;
   while ((x & 1) == 0) {
      ++c;
      x >>= 1;
   }
   return c;
#endif
}

#endif
