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/* __gmpfr_ceil_log2 - returns ceil(log(d)/log(2))
Copyright 1999-2004, 2006-2020 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU 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 3 of the License, or (at your
option) any later version.
The GNU 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 GNU MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, 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 _MPFR_IEEE_FLOATS
union mpfr_ieee_double_extract x;
x.d = d;
/* The cast below is useless in theory, but let us not depend on the
integer promotion rules (for instance, tcc is currently wrong). */
exp = (long) x.s.exp - 1023;
MPFR_ASSERTN (exp < 1023); /* fail on infinities */
x.s.exp = 1023; /* value for 1 <= d < 2 */
if (x.d != 1.0) /* d: not a power of two? */
exp++;
return exp;
#else /* _MPFR_IEEE_FLOATS */
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 *= 0.5)
exp--;
}
#endif /* _MPFR_IEEE_FLOATS */
return exp;
}
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