1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
|
/* mpfr_fac_ui -- factorial of a non-negative integer
Copyright (C) 2001 Free Software Foundation.
This file is part of the MPFR Library.
The MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.
The MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the MPFR Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#include "mpfr.h"
#include "mpfr-impl.h"
/* The computation of n! is done by
n!=prod^{n}_{i=1}i
*/
int
#if __STDC__
mpfr_fac_ui (mpfr_ptr y, unsigned long int x , mp_rnd_t rnd_mode)
#else
mpfr_fac_ui (y, x, rnd_mode)
mpfr_ptr y;
unsigned long x;
mp_rnd_t rnd_mode;
#endif
{
/****** Declaration ******/
mpfr_t t; /* Variable of Intermediary Calculation*/
int i;
int round, inexact = 0;
int boucle = 1;
mp_prec_t Ny; /* Precision of output variable */
mp_prec_t Nt; /* Precision of Intermediary Calculation variable */
mp_prec_t err; /* Precision of error */
/***** test x = 0 ******/
if (x == 0)
{
mpfr_set_ui (y, 1, GMP_RNDN); /* 0! = 1 */
return 0;
}
else
{
/* Initialisation of the Precision */
Ny=MPFR_PREC(y);
Nt=Ny+2*(int)_mpfr_ceil_log2((double)x)+10; /*compute the size of intermediary variable */
mpfr_init2(t, Nt);/* initialise of intermediary variable */
while (boucle)
{
inexact = mpfr_set_ui (t, 1, GMP_RNDZ);
for(i=2;i<=x;i++) /* compute factorial */
{
round = mpfr_mul_ui (t, t, i, GMP_RNDZ);
/* assume the first inexact product gives the sign
of difference: is that always correct? */
if (inexact == 0)
inexact = round;
}
err = Nt - 1 - (int) _mpfr_ceil_log2 ((double) Nt);
round = !inexact || mpfr_can_round (t,err,GMP_RNDZ,rnd_mode,Ny);
if (round)
{
round = mpfr_set (y, t, rnd_mode);
if (inexact == 0)
inexact = round;
boucle=0;
}
else
{
Nt=Nt+10;
/*initialise of intermediary variable */
mpfr_set_prec(t, Nt);
}
}
mpfr_clear(t);
return inexact;
}
}
|