/* mpn_pow_1 -- Compute powers R = U^exp.

   THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY.  THEY'RE ALMOST

   CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN

   FUTURE GNU MP RELEASES.

Copyright 2002, 2014 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify

it under the terms of either:

  * the GNU Lesser General Public License as published by the Free

    Software Foundation; either version 3 of the License, or (at your

    option) any later version.

or

  * the GNU General Public License as published by the Free Software

    Foundation; either version 2 of the License, or (at your option) any

    later version.

or both in parallel, as here.

The GNU MP Library is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY

or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

for more details.

You should have received copies of the GNU General Public License and the

GNU Lesser General Public License along with the GNU MP Library.  If not,

see https://www.gnu.org/licenses/.  */

#include "gmp.h"

#include "gmp-impl.h"

#include "longlong.h"

mp_size_t

mpn_pow_1 (mp_ptr rp, mp_srcptr bp, mp_size_t bn, mp_limb_t exp, mp_ptr tp)

{

  mp_limb_t x;

  int cnt, i;

  mp_size_t rn;

  int par;

  ASSERT (bn >= 1);

  /* FIXME: Add operand overlap criteria */

  if (exp <= 1)

    {

      if (exp == 0)

	{

	  rp[0] = 1;

	  return 1;

	}

      else

	{

	  MPN_COPY (rp, bp, bn);

	  return bn;

	}

    }

  /* Count number of bits in exp, and compute where to put initial square in

     order to magically get results in the entry rp.  Use simple code,

     optimized for small exp.  For large exp, the bignum operations will take

     so much time that the slowness of this code will be negligible.  */

  par = 0;

  cnt = GMP_LIMB_BITS;

  x = exp;

  do

    {

      par ^= x;

      cnt--;

      x >>= 1;

    } while (x != 0);

  exp <<= cnt;

  if (bn == 1)

    {

      mp_limb_t bl = bp[0];

      if ((cnt & 1) != 0)

	MP_PTR_SWAP (rp, tp);

      mpn_sqr (rp, bp, bn);

      rn = 2 * bn; rn -= rp[rn - 1] == 0;

      for (i = GMP_LIMB_BITS - cnt - 1;;)

	{

	  exp <<= 1;

	  if ((exp & GMP_LIMB_HIGHBIT) != 0)

	    {

	      rp[rn] = mpn_mul_1 (rp, rp, rn, bl);

	      rn += rp[rn] != 0;

	    }

	  if (--i == 0)

	    break;

	  mpn_sqr (tp, rp, rn);

	  rn = 2 * rn; rn -= tp[rn - 1] == 0;

	  MP_PTR_SWAP (rp, tp);

	}

    }

  else

    {

      if (((par ^ cnt) & 1) == 0)

	MP_PTR_SWAP (rp, tp);

      mpn_sqr (rp, bp, bn);

      rn = 2 * bn; rn -= rp[rn - 1] == 0;

      for (i = GMP_LIMB_BITS - cnt - 1;;)

	{

	  exp <<= 1;

	  if ((exp & GMP_LIMB_HIGHBIT) != 0)

	    {

	      rn = rn + bn - (mpn_mul (tp, rp, rn, bp, bn) == 0);

	      MP_PTR_SWAP (rp, tp);

	    }

	  if (--i == 0)

	    break;

	  mpn_sqr (tp, rp, rn);

	  rn = 2 * rn; rn -= tp[rn - 1] == 0;

	  MP_PTR_SWAP (rp, tp);

	}

    }

  return rn;

}