source/libs/gmp/gmp-src/mpz/remove.c

   1 /* mpz_remove -- divide out a factor and return its multiplicity.
   2
   3 Copyright 1998-2002, 2012 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 either:
   9
  10   * the GNU Lesser General Public License as published by the Free
  11     Software Foundation; either version 3 of the License, or (at your
  12     option) any later version.
  13
  14 or
  15
  16   * the GNU General Public License as published by the Free Software
  17     Foundation; either version 2 of the License, or (at your option) any
  18     later version.
  19
  20 or both in parallel, as here.
  21
  22 The GNU MP Library is distributed in the hope that it will be useful, but
  23 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  24 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  25 for more details.
  26
  27 You should have received copies of the GNU General Public License and the
  28 GNU Lesser General Public License along with the GNU MP Library.  If not,
  29 see https://www.gnu.org/licenses/.  */
  30
  31 #include "gmp.h"
  32 #include "gmp-impl.h"
  33
  34 mp_bitcnt_t
  35 mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
  36 {
  37   mp_bitcnt_t pwr;
  38   mp_srcptr fp;
  39   mp_size_t sn, fn, afn;
  40   mp_limb_t fp0;
  41
  42   sn = SIZ (src);
  43   fn = SIZ (f);
  44   fp = PTR (f);
  45   afn = ABS (fn);
  46   fp0 = fp[0];
  47
  48   if (UNLIKELY ((afn <= (fp0 == 1)) /* mpz_cmpabs_ui (f, 1) <= 0 */
  49                 | (sn == 0)))
  50     {
  51       /*  f = 0 or f = +- 1 or src = 0 */
  52       if (afn == 0)
  53         DIVIDE_BY_ZERO;
  54       mpz_set (dest, src);
  55       return 0;
  56     }
  57
  58   if ((fp0 & 1) != 0)
  59     { /* f is odd */
  60       mp_ptr dp;
  61       mp_size_t dn;
  62
  63       dn = ABS (sn);
  64       dp = MPZ_REALLOC (dest, dn);
  65
  66       pwr = mpn_remove (dp, &dn, PTR(src), dn, PTR(f), afn, ~(mp_bitcnt_t) 0);
  67
  68       SIZ (dest) = ((pwr & (fn < 0)) ^ (sn < 0)) ? -dn : dn;
  69     }
  70   else if (afn == (fp0 == 2))
  71     { /* mpz_cmpabs_ui (f, 2) == 0 */
  72       pwr = mpz_scan1 (src, 0);
  73       mpz_div_2exp (dest, src, pwr);
  74       if (pwr & (fn < 0)) /*((pwr % 2 == 1) && (SIZ (f) < 0))*/
  75         mpz_neg (dest, dest);
  76     }
  77   else
  78     { /* f != +-2 */
  79       mpz_t x, rem;
  80
  81       mpz_init (rem);
  82       mpz_init (x);
  83
  84       pwr = 0;
  85       mpz_tdiv_qr (x, rem, src, f);
  86       if (SIZ (rem) == 0)
  87         {
  88           mpz_t fpow[GMP_LIMB_BITS];            /* Really MP_SIZE_T_BITS */
  89           int p;
  90
  91 #if WANT_ORIGINAL_DEST
  92           mp_ptr dp;
  93           dp = PTR (dest);
  94 #endif
  95       /* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0).  It is an
  96          upper bound of the result we're seeking.  We could also shift down the
  97          operands so that they become odd, to make intermediate values
  98          smaller.  */
  99           mpz_init_set (fpow[0], f);
 100           mpz_swap (dest, x);
 101
 102           p = 1;
 103       /* Divide by f, f^2 ... f^(2^k) until we get a remainder for f^(2^k).  */
 104           while (ABSIZ (dest) >= 2 * ABSIZ (fpow[p - 1]) - 1)
 105             {
 106               mpz_init (fpow[p]);
 107               mpz_mul (fpow[p], fpow[p - 1], fpow[p - 1]);
 108               mpz_tdiv_qr (x, rem, dest, fpow[p]);
 109               if (SIZ (rem) != 0) {
 110                 mpz_clear (fpow[p]);
 111                 break;
 112               }
 113               mpz_swap (dest, x);
 114               p++;
 115             }
 116
 117           pwr = ((mp_bitcnt_t)1 << p) - 1;
 118
 119       /* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give
 120          a zero remainder.  */
 121           while (--p >= 0)
 122             {
 123               mpz_tdiv_qr (x, rem, dest, fpow[p]);
 124               if (SIZ (rem) == 0)
 125                 {
 126                   pwr += (mp_bitcnt_t)1 << p;
 127                   mpz_swap (dest, x);
 128                 }
 129               mpz_clear (fpow[p]);
 130             }
 131
 132 #if WANT_ORIGINAL_DEST
 133           if (PTR (x) == dp) {
 134             mpz_swap (dest, x);
 135             mpz_set (dest, x);
 136           }
 137 #endif
 138         }
 139       else
 140         mpz_set (dest, src);
 141
 142       mpz_clear (x);
 143       mpz_clear (rem);
 144     }
 145
 146   return pwr;
 147 }