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/* mpz_ui_pow_ui(res, base, exp) -- Set RES to BASE**EXP.
Copyright (C) 1991, 1993, 1994, 1996, 1997, 2000 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.
You should have received a copy of the GNU Library 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. */
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
static void mpz_pow2 _PROTO ((mpz_ptr r, mp_limb_t blimb, unsigned long int e, mp_limb_t rl));
void
#if __STDC__
mpz_ui_pow_ui (mpz_ptr r, unsigned long int b, unsigned long int e)
#else
mpz_ui_pow_ui (r, b, e)
mpz_ptr r;
unsigned long int b;
unsigned long int e;
#endif
{
mp_limb_t blimb = b;
mp_limb_t rl;
if (e == 0)
{
/* For x^0 we return 1, even if x is 0. */
r->_mp_d[0] = 1;
r->_mp_size = 1;
return;
}
/* Compute b^e as (b^n)^(e div n) * b^(e mod n), where n is chosen such that
the latter factor is the largest number small enough to fit in a limb. */
rl = 1;
while (e != 0 && blimb < ((mp_limb_t) 1 << BITS_PER_MP_LIMB/2))
{
if ((e & 1) != 0)
rl = rl * blimb;
blimb = blimb * blimb;
e = e >> 1;
}
/* rl is now b^(e mod n). (I.e., the latter factor above.) */
if (e == 0)
{
r->_mp_d[0] = rl;
r->_mp_size = rl != 0;
return;
}
mpz_pow2 (r, blimb, e, rl);
}
/* Multi-precision part of expontialization code. */
static void
#if __STDC__
mpz_pow2 (mpz_ptr r, mp_limb_t blimb, unsigned long int e, mp_limb_t rl)
#else
mpz_pow2 (r, blimb, e, rl)
mpz_ptr r;
mp_limb_t blimb;
unsigned long int e;
mp_limb_t rl;
#endif
{
mp_ptr rp, tp;
mp_size_t ralloc, rsize;
int cnt, i;
TMP_DECL (marker);
TMP_MARK (marker);
/* Over-estimate temporary space requirements somewhat. */
count_leading_zeros (cnt, blimb);
ralloc = e - cnt * e / BITS_PER_MP_LIMB + 1;
/* The two areas are used to alternatingly hold the input and receive the
product for mpn_mul. (Needed since mpn_mul_n requires that the product
is distinct from either input operand.) */
rp = (mp_ptr) TMP_ALLOC (ralloc * BYTES_PER_MP_LIMB);
tp = (mp_ptr) TMP_ALLOC (ralloc * BYTES_PER_MP_LIMB);
rp[0] = blimb;
rsize = 1;
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;
MP_PTR_SWAP (rp, tp);
if ((e & ((mp_limb_t) 1 << i)) != 0)
{
mp_limb_t cy;
cy = mpn_mul_1 (rp, rp, rsize, blimb);
rp[rsize] = cy;
rsize += cy != 0;
}
}
/* We will need rsize or rsize+1 limbs for the result. */
if (r->_mp_alloc <= rsize)
_mpz_realloc (r, rsize + 1);
/* Multiply the two factors (in rp,rsize and rl) and put the final result
in place. */
{
mp_limb_t cy;
cy = mpn_mul_1 (r->_mp_d, rp, rsize, rl);
(r->_mp_d)[rsize] = cy;
rsize += cy != 0;
}
r->_mp_size = rsize;
TMP_FREE (marker);
}
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