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
|
/* __gmpfr_ceil_log2 - returns ceil(log(d)/log(2))
Copyright 1999, 2000, 2001, 2002, 2003, 2004 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 "mpfr-impl.h"
/* returns ceil(log(d)/log(2)) if d > 0,
-1023 if d = +0,
and floor(log(-d)/log(2))+1 if d < 0*/
long
__gmpfr_ceil_log2 (double d)
{
long exp;
#if _GMP_IEEE_FLOATS
union ieee_double_extract x;
x.d = d;
exp = x.s.exp - 1023;
x.s.exp = 1023; /* value for 1 <= d < 2 */
if (x.d != 1.0) /* d: not a power of two? */
exp++;
return exp;
#else
double m;
if (d < 0.0)
return __gmpfr_floor_log2(-d)+1;
else if (d == 0.0)
return -1023;
else if (d >= 1.0)
{
exp = 0;
for( m= 1.0 ; m < d ; m *=2.0 )
exp++;
}
else
{
exp = 1;
for( m= 1.0 ; m >= d ; m *= (1.0/2.0) )
exp--;
}
#endif
return exp;
}
|
