/* mpz_pow_ui(res, base, exp) -- Set RES to BASE**EXP.

Copyright (C) 1991, 1993, 1994, 1996, 1997 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 the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.

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 Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

#ifdef BERKELEY_MP
#include "mp.h"
#endif
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"

#ifndef BERKELEY_MP
void
#if __STDC__
mpz_pow_ui (mpz_ptr r, mpz_srcptr b, unsigned long int e)
#else
mpz_pow_ui (r, b, e)
     mpz_ptr r;
     mpz_srcptr b;
     unsigned long int e;
#endif
#else /* BERKELEY_MP */
void
#if __STDC__
rpow (const MINT *b, signed short int e, MINT *r)
#else
rpow (b, e, r)
     const MINT *b;
     signed short int e;
     MINT *r;
#endif
#endif /* BERKELEY_MP */
{
  mp_ptr rp, bp, tp, xp;
  mp_size_t ralloc, rsize, bsize;
  int cnt, i;
  mp_limb_t blimb;
  TMP_DECL (marker);

  bsize = ABS (b->_mp_size);

  /* Single out cases that give result == 0 or 1.  These tests are here
     to simplify the general code below, not to optimize.  */
  if (e == 0)
    {
      r->_mp_d[0] = 1;
      r->_mp_size = 1;
      return;
    }
  if (bsize == 0
#ifdef BERKELEY_MP
      || e < 0
#endif
      )
    {
      r->_mp_size = 0;
      return;
    }

  bp = b->_mp_d;

  blimb = bp[bsize - 1];
  if (bsize == 1 && blimb < 0x100)
    {
      /* Estimate space requirements accurately.  Using the code from the
	 `else' path would over-estimate space requirements wildly.   */
      float lb = __mp_bases[blimb].chars_per_bit_exactly;
      ralloc = 3 + ((mp_size_t) (e / lb) / BITS_PER_MP_LIMB);
    }
  else
    {
      /* Over-estimate space requirements somewhat.  */
      count_leading_zeros (cnt, blimb);
      ralloc = bsize * e - cnt * e / BITS_PER_MP_LIMB + 2;
    }

  TMP_MARK (marker);

  /* The two areas are used to alternatingly hold the input and recieve the
     product for mpn_mul.  (This scheme is used to fulfill the requirements
     of mpn_mul; that the product space may not be the same as any of the
     input operands.)  */
  rp = (mp_ptr) TMP_ALLOC (ralloc * BYTES_PER_MP_LIMB);
  tp = (mp_ptr) TMP_ALLOC (ralloc * BYTES_PER_MP_LIMB);

  MPN_COPY (rp, bp, bsize);
  rsize = bsize;
  count_leading_zeros (cnt, e);

  for (i = BITS_PER_MP_LIMB - cnt - 2; i >= 0; i--)
    {
      mpn_mul_n (tp, rp, rp, rsize);
      rsize = 2 * rsize;
      rsize -= tp[rsize - 1] == 0;
      xp = tp; tp = rp; rp = xp;

      if ((e & ((mp_limb_t) 1 << i)) != 0)
	{
	  rsize = rsize + bsize - (mpn_mul (tp, rp, rsize, bp, bsize) == 0);
	  xp = tp; tp = rp; rp = xp;
	}
    }

  /* Now then we know the exact space requirements, reallocate if
     necessary.  */
  if (r->_mp_alloc < rsize)
    _mpz_realloc (r, rsize);

  MPN_COPY (r->_mp_d, rp, rsize);
  r->_mp_size = (e & 1) == 0 || b->_mp_size >= 0 ? rsize : -rsize;
  TMP_FREE (marker);
}
