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/* mpfr_nbits_ulong -- number of significant bits in an unsigned long
Copyright 2018-2020 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. */
#define MPFR_NEED_LONGLONG_H /* for count_leading_zeros */
#include "mpfr-impl.h"
/* count the number of significant bits of n, i.e.,
nbits(unsigned long) - count_leading_zeros (n) */
int
mpfr_nbits_ulong (unsigned long n)
{
int cnt;
MPFR_ASSERTD (n > 0);
#ifdef MPFR_LONG_WITHIN_LIMB
count_leading_zeros (cnt, (mp_limb_t) n);
cnt = GMP_NUMB_BITS - cnt;
#else
cnt = 0;
while (n >= 0x10000)
{
n >>= 16;
cnt += 16;
}
MPFR_ASSERTD (n <= 0xffff);
if (n >= 0x100)
{
n >>= 8;
cnt += 8;
}
MPFR_ASSERTD (n <= 0xff);
if (n >= 0x10)
{
n >>= 4;
cnt += 4;
}
MPFR_ASSERTD (n <= 0xf);
if (n >= 4)
{
n >>= 2;
cnt += 2;
}
MPFR_ASSERTD (n <= 3);
/* now n = 1, 2, or 3 */
cnt += 1 + (n >= 2);
#endif
MPFR_ASSERTD (cnt >= 0);
return cnt;
}
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