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Member "mpfr-4.0.2/src/uceil_log2.c" (7 Jan 2019, 1969 Bytes) of package /linux/misc/mpfr-4.0.2.tar.gz:


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    1 /* __gmpfr_ceil_log2 - returns ceil(log(d)/log(2))
    2 
    3 Copyright 1999-2004, 2006-2019 Free Software Foundation, Inc.
    4 Contributed by the AriC and Caramba projects, INRIA.
    5 
    6 This file is part of the GNU MPFR Library.
    7 
    8 The GNU MPFR Library is free software; you can redistribute it and/or modify
    9 it under the terms of the GNU Lesser General Public License as published by
   10 the Free Software Foundation; either version 3 of the License, or (at your
   11 option) any later version.
   12 
   13 The GNU MPFR Library is distributed in the hope that it will be useful, but
   14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
   15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
   16 License for more details.
   17 
   18 You should have received a copy of the GNU Lesser General Public License
   19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
   20 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
   21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
   22 
   23 #include "mpfr-impl.h"
   24 
   25 /* returns ceil(log(d)/log(2)) if d > 0,
   26    -1023 if d = +0,
   27    and floor(log(-d)/log(2))+1 if d < 0
   28 */
   29 long
   30 __gmpfr_ceil_log2 (double d)
   31 {
   32   long exp;
   33 #if _MPFR_IEEE_FLOATS
   34   union mpfr_ieee_double_extract x;
   35 
   36   x.d = d;
   37   /* The cast below is useless in theory, but let us not depend on the
   38      integer promotion rules (for instance, tcc is currently wrong). */
   39   exp = (long) x.s.exp - 1023;
   40   MPFR_ASSERTN (exp < 1023);  /* fail on infinities */
   41   x.s.exp = 1023; /* value for 1 <= d < 2 */
   42   if (x.d != 1.0) /* d: not a power of two? */
   43     exp++;
   44   return exp;
   45 #else /* _MPFR_IEEE_FLOATS */
   46   double m;
   47 
   48   if (d < 0.0)
   49     return __gmpfr_floor_log2 (-d) + 1;
   50   else if (d == 0.0)
   51     return -1023;
   52   else if (d >= 1.0)
   53     {
   54       exp = 0;
   55       for (m = 1.0; m < d; m *= 2.0)
   56         exp++;
   57     }
   58   else
   59     {
   60       exp = 1;
   61       for (m = 1.0; m >= d; m *= 0.5)
   62         exp--;
   63     }
   64 #endif /* _MPFR_IEEE_FLOATS */
   65   return exp;
   66 }
   67