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Annotation of OpenXM_contrib/gmp/mpz/remove.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpz_remove -- divide out a factor and return its multiplicity.
                      2:
                      3: Copyright (C) 1998, 1999, 2000 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 Lesser General Public License as published by
                      9: the Free Software Foundation; either version 2.1 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 Lesser General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Lesser 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:
                     25: unsigned long int
                     26: #if __STDC__
                     27: mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
                     28: #else
                     29: mpz_remove (dest, src, f)
                     30:      mpz_ptr dest;
                     31:      mpz_srcptr src;
                     32:      mpz_srcptr f;
                     33: #endif
                     34: {
                     35:   mpz_t fpow[40];              /* inexhaustible...until year 2020 or so */
                     36:   mpz_t x, rem;
                     37:   unsigned long int pwr;
                     38:   int p;
                     39:
                     40:   if (mpz_cmp_ui (f, 1) <= 0 || mpz_sgn (src) == 0)
                     41:     DIVIDE_BY_ZERO;
                     42:   if (mpz_cmp_ui (f, 2) == 0)
                     43:     {
                     44:       unsigned long int s0;
                     45:       s0 = mpz_scan1 (src, 0);
                     46:       mpz_div_2exp (dest, src, s0);
                     47:       return s0;
                     48:     }
                     49:
                     50:   /* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0).  It is an
                     51:      upper bound of the result we're seeking.  We could also shift down the
                     52:      operands so that they become odd, to make intermediate values smaller.  */
                     53:
                     54:   mpz_init (rem);
                     55:   mpz_init (x);
                     56:
                     57:   pwr = 0;
                     58:   mpz_init (fpow[0]);
                     59:   mpz_set (fpow[0], f);
                     60:   mpz_set (dest, src);
                     61:
                     62:   /* Divide by f, f^2, ..., f^(2^k) until we get a remainder for f^(2^k).  */
                     63:   for (p = 0;; p++)
                     64:     {
                     65:       mpz_tdiv_qr (x, rem, dest, fpow[p]);
                     66:       if (SIZ (rem) != 0)
                     67:        break;
                     68:       mpz_init (fpow[p + 1]);
                     69:       mpz_mul (fpow[p + 1], fpow[p], fpow[p]);
                     70:       mpz_set (dest, x);
                     71:     }
                     72:
                     73:   pwr = (1 << p) - 1;
                     74:
                     75:   mpz_clear (fpow[p]);
                     76:
                     77:   /* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give a
                     78:      zero remainder.  */
                     79:   while (--p >= 0)
                     80:     {
                     81:       mpz_tdiv_qr (x, rem, dest, fpow[p]);
                     82:       if (SIZ (rem) == 0)
                     83:        {
                     84:          pwr += 1 << p;
                     85:          mpz_set (dest, x);
                     86:        }
                     87:       mpz_clear (fpow[p]);
                     88:     }
                     89:
                     90:   mpz_clear (x);
                     91:   mpz_clear (rem);
                     92:   return pwr;
                     93: }