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      1 /* mpfr_nbits_ulong -- number of significant bits in an unsigned long
      2    mpfr_nbits_uj    -- number of significant bits in an uintmax_t
      3 
      4 Copyright 2018-2023 Free Software Foundation, Inc.
      5 Contributed by the AriC and Caramba projects, INRIA.
      6 
      7 This file is part of the GNU MPFR Library.
      8 
      9 The GNU MPFR Library is free software; you can redistribute it and/or modify
     10 it under the terms of the GNU Lesser General Public License as published by
     11 the Free Software Foundation; either version 3 of the License, or (at your
     12 option) any later version.
     13 
     14 The GNU MPFR Library is distributed in the hope that it will be useful, but
     15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     16 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
     17 License for more details.
     18 
     19 You should have received a copy of the GNU Lesser General Public License
     20 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
     21 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
     22 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
     23 
     24 #define MPFR_NEED_LONGLONG_H  /* for count_leading_zeros */
     25 #define MPFR_NEED_INTMAX_H
     26 #include "mpfr-impl.h"
     27 
     28 /* count the number of significant bits of n, i.e.,
     29    nbits(unsigned long) - count_leading_zeros (n) */
     30 int
     31 mpfr_nbits_ulong (unsigned long n)
     32 {
     33   int cnt;
     34 
     35   MPFR_ASSERTD (n > 0);
     36 
     37 #ifdef MPFR_LONG_WITHIN_LIMB
     38 
     39   count_leading_zeros (cnt, (mp_limb_t) n);
     40   cnt = GMP_NUMB_BITS - cnt;
     41 
     42 #else
     43 
     44   cnt = 0;
     45 
     46   while (n >= 0x10000)
     47     {
     48       n >>= 16;
     49       cnt += 16;
     50     }
     51 
     52   MPFR_ASSERTD (n <= 0xffff);
     53 
     54   if (n >= 0x100)
     55     {
     56       n >>= 8;
     57       cnt += 8;
     58     }
     59 
     60   MPFR_ASSERTD (n <= 0xff);
     61 
     62   if (n >= 0x10)
     63     {
     64       n >>= 4;
     65       cnt += 4;
     66     }
     67 
     68   MPFR_ASSERTD (n <= 0xf);
     69 
     70   if (n >= 4)
     71     {
     72       n >>= 2;
     73       cnt += 2;
     74     }
     75 
     76   MPFR_ASSERTD (n <= 3);
     77 
     78   /* now n = 1, 2, or 3 */
     79   cnt += 1 + (n >= 2);
     80 
     81 #endif
     82 
     83   MPFR_ASSERTD (cnt >= 0);
     84   return cnt;
     85 }
     86 
     87 #ifdef _MPFR_H_HAVE_INTMAX_T
     88 /* count the number of significant bits of n, i.e.,
     89    nbits(uintmax_t) - count_leading_zeros (n) */
     90 int
     91 mpfr_nbits_uj (uintmax_t n)
     92 {
     93   int cnt;
     94 
     95   MPFR_ASSERTD (n > 0);
     96 
     97   cnt = 0;
     98 
     99   while (n >= 0x10000)
    100     {
    101       n >>= 16;
    102       cnt += 16;
    103     }
    104 
    105   MPFR_ASSERTD (n <= 0xffff);
    106 
    107   if (n >= 0x100)
    108     {
    109       n >>= 8;
    110       cnt += 8;
    111     }
    112 
    113   MPFR_ASSERTD (n <= 0xff);
    114 
    115   if (n >= 0x10)
    116     {
    117       n >>= 4;
    118       cnt += 4;
    119     }
    120 
    121   MPFR_ASSERTD (n <= 0xf);
    122 
    123   if (n >= 4)
    124     {
    125       n >>= 2;
    126       cnt += 2;
    127     }
    128 
    129   MPFR_ASSERTD (n <= 3);
    130 
    131   /* now n = 1, 2, or 3 */
    132   cnt += 1 + (n >= 2);
    133 
    134   MPFR_ASSERTD (cnt >= 0);
    135   return cnt;
    136 }
    137 #endif
    138