/* mpf_pow_ui -- Compute b^e.

Copyright 1998, 1999, 2001, 2012, 2015 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"

/* This uses a plain right-to-left square-and-multiply algorithm.

   FIXME: When popcount(e) is not too small, it would probably speed things up

   to use a k-ary sliding window algorithm.  */

void

mpf_pow_ui (mpf_ptr r, mpf_srcptr b, unsigned long int e)

{

  mpf_t t;

  int cnt;

  if (e <= 1)

    {

      if (e == 0)

	mpf_set_ui (r, 1);

      else

	mpf_set (r, b);

      return;

    }

  count_leading_zeros (cnt, (mp_limb_t) e);

  cnt = GMP_LIMB_BITS - 1 - cnt;

  /* Increase computation precision as a function of the exponent.  Adding

     log2(popcount(e) + log2(e)) bits should be sufficient, but we add log2(e),

     i.e. much more.  With mpf's rounding of precision to whole limbs, this

     will be excessive only when limbs are artificially small.  */

  mpf_init2 (t, mpf_get_prec (r) + cnt);

  mpf_set (t, b);		/* consume most significant bit */

  while (--cnt > 0)

    {

      mpf_mul (t, t, t);

      if ((e >> cnt) & 1)

	mpf_mul (t, t, b);

    }

  /* Do the last iteration specially in order to save a copy operation.  */

  if (e & 1)

    {

      mpf_mul (t, t, t);

      mpf_mul (r, t, b);

    }

  else

    {

      mpf_mul (r, t, t);

    }

  mpf_clear (t);

}