/*
* BigInt Random Generation
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/bigint.h>
#include <botan/parsing.h>
#include <botan/internal/rounding.h>

namespace Botan {

/*
* Randomize this number
*/
void BigInt::randomize(RandomNumberGenerator& rng,
                       size_t bitsize, bool set_high_bit)
   {
   set_sign(Positive);

   if(bitsize == 0)
      {
      clear();
      }
   else
      {
      secure_vector<byte> array = rng.random_vec(round_up(bitsize, 8) / 8);

      // Always cut unwanted bits
      if(bitsize % 8)
         array[0] &= 0xFF >> (8 - (bitsize % 8));

      // Set the highest bit if wanted
      if (set_high_bit)
         array[0] |= 0x80 >> ((bitsize % 8) ? (8 - bitsize % 8) : 0);

      binary_decode(array);
      }
   }

/*
* Generate a random integer within given range
*/
BigInt BigInt::random_integer(RandomNumberGenerator& rng,
                              const BigInt& min, const BigInt& max)
   {
   BigInt delta_upper_bound = max - min - 1;

   if(delta_upper_bound < 0)
      throw Invalid_Argument("random_integer: invalid min/max values");

   // Choose x in [0, delta_upper_bound]
   BigInt x;
   do {
      auto bitsize = delta_upper_bound.bits();
      x.randomize(rng, bitsize, false);
   } while(x > delta_upper_bound);

   return min + x;
   }

}