sysdeps/ieee754/dbl-64/s_logb.c

   1 /* Compute radix independent exponent.
   2    Copyright (C) 2011-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <math.h>
  20
  21 #include <math_private.h>
  22 #include <libm-alias-double.h>
  23 #include <fix-int-fp-convert-zero.h>
  24 #include <math-use-builtins.h>
  25
  26 double
  27 __logb (double x)
  28 {
  29 #if USE_LOGB_BUILTIN
  30   return __builtin_logb (x);
  31 #else
  32   int64_t ix, ex;
  33
  34   EXTRACT_WORDS64 (ix, x);
  35   ix &= UINT64_C(0x7fffffffffffffff);
  36   if (ix == 0)
  37     return -1.0 / fabs (x);
  38   ex = ix >> 52;
  39   if (ex == 0x7ff)
  40     return x * x;
  41   if (__glibc_unlikely (ex == 0))
  42     {
  43       int m = __builtin_clzll (ix);
  44       ex -= m - 12;
  45     }
  46   if (FIX_INT_FP_CONVERT_ZERO && ex == 1023)
  47     return 0.0;
  48   return (double) (ex - 1023);
  49 #endif /* !USE_LOGB_BUILTIN  */
  50 }
  51 #ifndef __logb
  52 libm_alias_double (__logb, logb)
  53 #endif