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 1.1.1.1

1.1       maekawa     1: /* mpz_ui_pow_ui(res, base, exp) -- Set RES to BASE**EXP.
                      2:
                      3: Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the GNU MP Library.
                      6:
                      7: The GNU MP Library is free software; you can redistribute it and/or modify
                      8: it under the terms of the GNU Library General Public License as published by
                      9: the Free Software Foundation; either version 2 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Library General Public License
                     18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24: #include "longlong.h"
                     25:
                     26: void
                     27: #if __STDC__
                     28: mpz_ui_pow_ui (mpz_ptr r, unsigned long int b, unsigned long int e)
                     29: #else
                     30: mpz_ui_pow_ui (r, b, e)
                     31:      mpz_ptr r;
                     32:      unsigned long int b;
                     33:      unsigned long int e;
                     34: #endif
                     35: {
                     36:   mp_ptr rp, tp, xp;
                     37:   mp_size_t rsize;
                     38:   int cnt, i;
                     39:   mp_limb_t blimb = b;
                     40:   TMP_DECL (marker);
                     41:
                     42:   /* Single out cases that give result == 0 or 1.  These tests are here
                     43:      to simplify the general code below, not to optimize.  */
                     44:   if (e == 0)
                     45:     {
                     46:       r->_mp_d[0] = 1;
                     47:       r->_mp_size = 1;
                     48:       return;
                     49:     }
                     50:   if (blimb == 0)
                     51:     {
                     52:       r->_mp_size = 0;
                     53:       return;
                     54:     }
                     55:
                     56:   if (blimb < 0x100)
                     57:     {
                     58:       /* Estimate space requirements accurately.  Using the code from the
                     59:         `else' path would over-estimate space requirements wildly.   */
                     60:       float lb = __mp_bases[blimb].chars_per_bit_exactly;
                     61:       rsize = 2 + ((mp_size_t) (e / lb) / BITS_PER_MP_LIMB);
                     62:     }
                     63:   else
                     64:     {
                     65:       /* Over-estimate space requirements somewhat.  */
                     66:       count_leading_zeros (cnt, blimb);
                     67:       rsize = e - cnt * e / BITS_PER_MP_LIMB + 1;
                     68:     }
                     69:
                     70:   TMP_MARK (marker);
                     71:
                     72:   /* The two areas are used to alternatingly hold the input and recieve the
                     73:      product for mpn_mul.  (This scheme is used to fulfill the requirements
                     74:      of mpn_mul; that the product space may not be the same as any of the
                     75:      input operands.)  */
                     76:   rp = (mp_ptr) TMP_ALLOC (rsize * BYTES_PER_MP_LIMB);
                     77:   tp = (mp_ptr) TMP_ALLOC (rsize * BYTES_PER_MP_LIMB);
                     78:
                     79:   rp[0] = blimb;
                     80:   rsize = 1;
                     81:   count_leading_zeros (cnt, e);
                     82:
                     83:   for (i = BITS_PER_MP_LIMB - cnt - 2; i >= 0; i--)
                     84:     {
                     85:       mpn_mul_n (tp, rp, rp, rsize);
                     86:       rsize = 2 * rsize;
                     87:       rsize -= tp[rsize - 1] == 0;
                     88:       xp = tp; tp = rp; rp = xp;
                     89:
                     90:       if ((e & ((mp_limb_t) 1 << i)) != 0)
                     91:        {
                     92:          mp_limb_t cy;
                     93:          cy = mpn_mul_1 (tp, rp, rsize, blimb);
                     94:          if (cy != 0)
                     95:            {
                     96:              tp[rsize] = cy;
                     97:              rsize++;
                     98:            }
                     99:          xp = tp; tp = rp; rp = xp;
                    100:        }
                    101:     }
                    102:
                    103:   /* Now then we know the exact space requirements, reallocate if
                    104:      necessary.  */
                    105:   if (r->_mp_alloc < rsize)
                    106:     _mpz_realloc (r, rsize);
                    107:
                    108:   MPN_COPY (r->_mp_d, rp, rsize);
                    109:   r->_mp_size = rsize;
                    110:   TMP_FREE (marker);
                    111: }