Return to bin_uiui.c CVS log

Up to [local] / OpenXM_contrib / gmp / mpz

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

1.1       maekawa     1: /* mpz_bin_uiui - compute n over k.
                      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: #include "longlong.h"
                     25:
                     26:
                     27: /* Avoid reallocs by rounding up any new size */
                     28: #define ROUNDUP_MASK  15
                     29:
                     30: /* Enhancement: use mpn_divexact_1 when it exists */
                     31: #define MULDIV()                                                \
                     32:   MPZ_REALLOC (r, (SIZ(r)+1)|ROUNDUP_MASK);                     \
                     33:   PTR(r)[SIZ(r)] = mpn_mul_1 (PTR(r), PTR(r), SIZ(r), nacc);    \
                     34:   ASSERT_NOCARRY (mpn_divrem_1 (PTR(r), (mp_size_t) 0,          \
                     35:                                 PTR(r), SIZ(r)+1, kacc));       \
                     36:   SIZ(r) += (PTR(r)[SIZ(r)] != 0);
                     37:
                     38: void
                     39: #if __STDC__
                     40: mpz_bin_uiui (mpz_ptr r, unsigned long int n, unsigned long int k)
                     41: #else
                     42: mpz_bin_uiui (r, n, k)
                     43:      mpz_ptr r;
                     44:      unsigned long int n;
                     45:      unsigned long int k;
                     46: #endif
                     47: {
                     48:   unsigned long int  i, j;
                     49:   mp_limb_t          nacc, kacc;
                     50:   unsigned long int  cnt;
                     51:
                     52:   /* bin(n,k) = 0 if k>n. */
                     53:   if (n < k)
                     54:     {
                     55:       mpz_set_ui (r, 0);
                     56:       return;
                     57:     }
                     58:
                     59:   /* Rewrite bin(n,k) as bin(n,n-k) if that is smaller. */
                     60:   k = MIN (k, n-k);
                     61:
                     62:   /* bin(n,0) = 1 */
                     63:   if (k == 0)
                     64:     {
                     65:       mpz_set_ui (r, 1);
                     66:       return;
                     67:     }
                     68:
                     69:   j = n - k + 1;
                     70:   mpz_set_ui (r, j);
                     71:
                     72:   /* Initialize accumulators.  */
                     73:   nacc = 1;
                     74:   kacc = 1;
                     75:
                     76:   cnt = 0;
                     77:   for (i = 2; i <= k; i++)
                     78:     {
                     79:       mp_limb_t n1, n0, k1, k0;
                     80:
                     81:       j++;
                     82: #if 0
                     83:       /* Remove common multiples of 2.  This will allow us to accumulate
                     84:          more in nacc and kacc before we need a bignum step.  It would make
                     85:          sense to cancel factors of 3, 5, etc too, but this would be best
                     86:          handled by sieving out factors.  Alternatively, we could perform a
                     87:          gcd of the accumulators just as they have overflown, and keep
                     88:          accumulating until the gcd doesn't remove a significant factor.  */
                     89:       while (((nacc | kacc) & 1) == 0)
                     90:         {
                     91:           nacc >>= 1;
                     92:           kacc >>= 1;
                     93:         }
                     94: #else
                     95:       cnt = ((nacc | kacc) & 1) ^ 1;
                     96:       nacc >>= cnt;
                     97:       kacc >>= cnt;
                     98: #endif
                     99:       /* Accumulate next multiples.  */
                    100:       umul_ppmm (n1, n0, nacc, j);
                    101:       umul_ppmm (k1, k0, kacc, i);
                    102:       if (n1 != 0)
                    103:         {
                    104:           /* Accumulator overflow.  Perform bignum step.  */
                    105:           MULDIV ();
                    106:           nacc = j;
                    107:           kacc = i;
                    108:         }
                    109:       else
                    110:         {
                    111:           if (k1 != 0) abort ();
                    112:           /* Save new products in accumulators to keep accumulating.  */
                    113:           nacc = n0;
                    114:           kacc = k0;
                    115:         }
                    116:     }
                    117:
                    118:   /* Take care of whatever is left in accumulators.  */
                    119:   MULDIV ();
                    120: }