1 /* mpz_ui_pow_ui(res, base, exp) -- Set RES to BASE**EXP.
3 Copyright (C) 1991, 1993, 1994, 1996, 1997, 2000 Free Software Foundation,
6 This file is part of the GNU MP Library.
8 The GNU MP Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 2.1 of the License, or (at your
11 option) any later version.
13 The GNU MP Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MP Library; see the file COPYING.LIB. If not, write to
20 the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
21 MA 02111-1307, USA. */
28 static void mpz_pow2 _PROTO ((mpz_ptr r, mp_limb_t blimb, unsigned long int e, mp_limb_t rl));
32 mpz_ui_pow_ui (mpz_ptr r, unsigned long int b, unsigned long int e)
34 mpz_ui_pow_ui (r, b, e)
45 /* For x^0 we return 1, even if x is 0. */
51 /* Compute b^e as (b^n)^(e div n) * b^(e mod n), where n is chosen such that
52 the latter factor is the largest number small enough to fit in a limb. */
55 while (e != 0 && blimb < ((mp_limb_t) 1 << BITS_PER_MP_LIMB/2))
59 blimb = blimb * blimb;
63 /* rl is now b^(e mod n). (I.e., the latter factor above.) */
68 r->_mp_size = rl != 0;
72 mpz_pow2 (r, blimb, e, rl);
75 /* Multi-precision part of expontialization code. */
78 mpz_pow2 (mpz_ptr r, mp_limb_t blimb, unsigned long int e, mp_limb_t rl)
80 mpz_pow2 (r, blimb, e, rl)
88 mp_size_t ralloc, rsize;
94 /* Over-estimate temporary space requirements somewhat. */
95 count_leading_zeros (cnt, blimb);
96 ralloc = e - cnt * e / BITS_PER_MP_LIMB + 1;
98 /* The two areas are used to alternatingly hold the input and receive the
99 product for mpn_mul. (Needed since mpn_mul_n requires that the product
100 is distinct from either input operand.) */
101 rp = (mp_ptr) TMP_ALLOC (ralloc * BYTES_PER_MP_LIMB);
102 tp = (mp_ptr) TMP_ALLOC (ralloc * BYTES_PER_MP_LIMB);
107 count_leading_zeros (cnt, e);
108 for (i = BITS_PER_MP_LIMB - cnt - 2; i >= 0; i--)
110 mpn_mul_n (tp, rp, rp, rsize);
112 rsize -= tp[rsize - 1] == 0;
113 MP_PTR_SWAP (rp, tp);
115 if ((e & ((mp_limb_t) 1 << i)) != 0)
118 cy = mpn_mul_1 (rp, rp, rsize, blimb);
124 /* We will need rsize or rsize+1 limbs for the result. */
125 if (r->_mp_alloc <= rsize)
126 _mpz_realloc (r, rsize + 1);
128 /* Multiply the two factors (in rp,rsize and rl) and put the final result
132 cy = mpn_mul_1 (r->_mp_d, rp, rsize, rl);
133 (r->_mp_d)[rsize] = cy;