Return to ui_pow_ui.c CVS log

Up to [local] / OpenXM_contrib / gmp / mpz

Annotation of OpenXM_contrib/gmp/mpz/ui_pow_ui.c, Revision 1.1.1.2

1.1       maekawa     1: /* mpz_ui_pow_ui(res, base, exp) -- Set RES to BASE**EXP.
                      2:
1.1.1.2 ! maekawa     3: Copyright (C) 1991, 1993, 1994, 1996, 1997, 2000 Free Software Foundation,
        !             4: Inc.
1.1       maekawa     5:
                      6: This file is part of the GNU MP Library.
                      7:
                      8: The GNU MP Library is free software; you can redistribute it and/or modify
1.1.1.2 ! maekawa     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
1.1       maekawa    11: option) any later version.
                     12:
                     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
1.1.1.2 ! maekawa    15: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
1.1       maekawa    16: License for more details.
                     17:
1.1.1.2 ! maekawa    18: You should have received a copy of the GNU Lesser General Public License
1.1       maekawa    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. */
                     22:
                     23: #include "gmp.h"
                     24: #include "gmp-impl.h"
                     25: #include "longlong.h"
                     26:
1.1.1.2 ! maekawa    27:
        !            28: static void mpz_pow2 _PROTO ((mpz_ptr r, mp_limb_t blimb, unsigned long int e, mp_limb_t rl));
        !            29:
1.1       maekawa    30: void
                     31: #if __STDC__
                     32: mpz_ui_pow_ui (mpz_ptr r, unsigned long int b, unsigned long int e)
                     33: #else
                     34: mpz_ui_pow_ui (r, b, e)
                     35:      mpz_ptr r;
                     36:      unsigned long int b;
                     37:      unsigned long int e;
                     38: #endif
                     39: {
                     40:   mp_limb_t blimb = b;
1.1.1.2 ! maekawa    41:   mp_limb_t rl;
1.1       maekawa    42:
                     43:   if (e == 0)
                     44:     {
1.1.1.2 ! maekawa    45:       /* For x^0 we return 1, even if x is 0.  */
1.1       maekawa    46:       r->_mp_d[0] = 1;
                     47:       r->_mp_size = 1;
                     48:       return;
                     49:     }
                     50:
1.1.1.2 ! maekawa    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.  */
        !            53:
        !            54:   rl = 1;
        !            55:   while (e != 0 && blimb < ((mp_limb_t) 1 << BITS_PER_MP_LIMB/2))
1.1       maekawa    56:     {
1.1.1.2 ! maekawa    57:       if ((e & 1) != 0)
        !            58:        rl = rl * blimb;
        !            59:       blimb = blimb * blimb;
        !            60:       e = e >> 1;
1.1       maekawa    61:     }
1.1.1.2 ! maekawa    62:
        !            63:   /* rl is now b^(e mod n).  (I.e., the latter factor above.)  */
        !            64:
        !            65:   if (e == 0)
1.1       maekawa    66:     {
1.1.1.2 ! maekawa    67:       r->_mp_d[0] = rl;
        !            68:       r->_mp_size = rl != 0;
        !            69:       return;
1.1       maekawa    70:     }
                     71:
1.1.1.2 ! maekawa    72:   mpz_pow2 (r, blimb, e, rl);
        !            73: }
        !            74:
        !            75: /* Multi-precision part of expontialization code.  */
        !            76: static void
        !            77: #if __STDC__
        !            78: mpz_pow2 (mpz_ptr r, mp_limb_t blimb, unsigned long int e, mp_limb_t rl)
        !            79: #else
        !            80: mpz_pow2 (r, blimb, e, rl)
        !            81:      mpz_ptr r;
        !            82:      mp_limb_t blimb;
        !            83:      unsigned long int e;
        !            84:      mp_limb_t rl;
        !            85: #endif
        !            86: {
        !            87:   mp_ptr rp, tp;
        !            88:   mp_size_t ralloc, rsize;
        !            89:   int cnt, i;
        !            90:   TMP_DECL (marker);
        !            91:
1.1       maekawa    92:   TMP_MARK (marker);
                     93:
1.1.1.2 ! maekawa    94:   /* Over-estimate temporary space requirements somewhat.  */
        !            95:   count_leading_zeros (cnt, blimb);
        !            96:   ralloc = e - cnt * e / BITS_PER_MP_LIMB + 1;
        !            97:
        !            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);
1.1       maekawa   103:
                    104:   rp[0] = blimb;
                    105:   rsize = 1;
                    106:
1.1.1.2 ! maekawa   107:   count_leading_zeros (cnt, e);
1.1       maekawa   108:   for (i = BITS_PER_MP_LIMB - cnt - 2; i >= 0; i--)
                    109:     {
                    110:       mpn_mul_n (tp, rp, rp, rsize);
                    111:       rsize = 2 * rsize;
                    112:       rsize -= tp[rsize - 1] == 0;
1.1.1.2 ! maekawa   113:       MP_PTR_SWAP (rp, tp);
1.1       maekawa   114:
                    115:       if ((e & ((mp_limb_t) 1 << i)) != 0)
                    116:        {
                    117:          mp_limb_t cy;
1.1.1.2 ! maekawa   118:          cy = mpn_mul_1 (rp, rp, rsize, blimb);
        !           119:          rp[rsize] = cy;
        !           120:          rsize += cy != 0;
1.1       maekawa   121:        }
                    122:     }
                    123:
1.1.1.2 ! maekawa   124:   /* We will need rsize or rsize+1 limbs for the result.  */
        !           125:   if (r->_mp_alloc <= rsize)
        !           126:     _mpz_realloc (r, rsize + 1);
        !           127:
        !           128:   /* Multiply the two factors (in rp,rsize and rl) and put the final result
        !           129:      in place.  */
        !           130:   {
        !           131:     mp_limb_t cy;
        !           132:     cy = mpn_mul_1 (r->_mp_d, rp, rsize, rl);
        !           133:     (r->_mp_d)[rsize] = cy;
        !           134:     rsize += cy != 0;
        !           135:   }
1.1       maekawa   136:
                    137:   r->_mp_size = rsize;
                    138:   TMP_FREE (marker);
                    139: }