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Annotation of OpenXM_contrib/gmp/mpfr/factorial.c, Revision 1.1.1.1

1.1       ohara       1: /* mpfr_fac_ui -- factorial of a non-negative integer
                      2:
                      3: Copyright 2001 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the MPFR Library.
                      6:
                      7: The MPFR 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 MPFR 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 MPFR 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 "mpfr.h"
                     25: #include "mpfr-impl.h"
                     26:
                     27:  /* The computation of n! is done by
                     28:
                     29:     n!=prod^{n}_{i=1}i
                     30:  */
                     31:
                     32: int
                     33: mpfr_fac_ui (mpfr_ptr y, unsigned long int x , mp_rnd_t rnd_mode)
                     34: {
                     35:
                     36:   /****** Declaration ******/
                     37:
                     38:     mpfr_t t;       /* Variable of Intermediary Calculation*/
                     39:     int i;
                     40:     int round, inexact = 0;
                     41:     int boucle = 1;
                     42:
                     43:     mp_prec_t Ny;   /* Precision of output variable */
                     44:     mp_prec_t Nt;   /* Precision of Intermediary Calculation variable */
                     45:     mp_prec_t err;  /* Precision of error */
                     46:
                     47:   /***** test x = 0  ******/
                     48:
                     49:     if (x == 0)
                     50:       {
                     51:        mpfr_set_ui (y, 1, GMP_RNDN); /* 0! = 1 */
                     52:        return 0;
                     53:       }
                     54:     else
                     55:       {
                     56:         /* Initialisation of the Precision */
                     57:        Ny=MPFR_PREC(y);
                     58:
                     59:        Nt=Ny+2*(int)_mpfr_ceil_log2((double)x)+10; /*compute the size of intermediary variable */
                     60:
                     61:
                     62:         mpfr_init2(t, Nt);/* initialise of intermediary variable */
                     63:
                     64:         while (boucle)
                     65:           {
                     66:             inexact = mpfr_set_ui (t, 1, GMP_RNDZ);
                     67:
                     68:             for(i=2;i<=x;i++)              /* compute factorial */
                     69:               {
                     70:                 round = mpfr_mul_ui (t, t, i, GMP_RNDZ);
                     71:                 /* assume the first inexact product gives the sign
                     72:                    of difference: is that always correct? */
                     73:                 if (inexact == 0)
                     74:                   inexact = round;
                     75:               }
                     76:
                     77:             err = Nt - 1 - (int) _mpfr_ceil_log2 ((double) Nt);
                     78:
                     79:             round = !inexact || mpfr_can_round (t,err,GMP_RNDZ,rnd_mode,Ny);
                     80:
                     81:             if (round)
                     82:               {
                     83:                 round = mpfr_set (y, t, rnd_mode);
                     84:                  if (inexact == 0)
                     85:                     inexact = round;
                     86:                  boucle=0;
                     87:                }
                     88:              else
                     89:                {
                     90:                  Nt=Nt+10;
                     91:                  /*initialise of intermediary variable */
                     92:                  mpfr_set_prec(t, Nt);
                     93:                }
                     94:          }
                     95:
                     96:          mpfr_clear(t);
                     97:           return inexact;
                     98:
                     99:     }
                    100: }
                    101:
                    102:
                    103:
                    104: