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Annotation of OpenXM_contrib/gmp/mpz/remove.c, Revision 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: }