kc3-lang/gnulib/lib/frexp.c

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• Hash : 281b825e
  Author :
  Date : 2018-01-01T00:57:25
  

  maint: Run 'make update-copyright'
  

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• lib/frexp.c

• /* Split a double into fraction and mantissa.
     Copyright (C) 2007-2018 Free Software Foundation, Inc.
  
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 3 of the License, or
     (at your option) any later version.
  
     This program 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 General Public License for more details.
  
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  
  /* Written by Paolo Bonzini <bonzini@gnu.org>, 2003, and
     Bruno Haible <bruno@clisp.org>, 2007.  */
  
  #if ! defined USE_LONG_DOUBLE
  # include <config.h>
  #endif
  
  /* Specification.  */
  #include <math.h>
  
  #include <float.h>
  #ifdef USE_LONG_DOUBLE
  # include "isnanl-nolibm.h"
  # include "fpucw.h"
  #else
  # include "isnand-nolibm.h"
  #endif
  
  /* This file assumes FLT_RADIX = 2.  If FLT_RADIX is a power of 2 greater
     than 2, or not even a power of 2, some rounding errors can occur, so that
     then the returned mantissa is only guaranteed to be <= 1.0, not < 1.0.  */
  
  #ifdef USE_LONG_DOUBLE
  # define FUNC frexpl
  # define DOUBLE long double
  # define ISNAN isnanl
  # define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING
  # define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING ()
  # define END_ROUNDING() END_LONG_DOUBLE_ROUNDING ()
  # define L_(literal) literal##L
  #else
  # define FUNC frexp
  # define DOUBLE double
  # define ISNAN isnand
  # define DECL_ROUNDING
  # define BEGIN_ROUNDING()
  # define END_ROUNDING()
  # define L_(literal) literal
  #endif
  
  DOUBLE
  FUNC (DOUBLE x, int *expptr)
  {
    int sign;
    int exponent;
    DECL_ROUNDING
  
    /* Test for NaN, infinity, and zero.  */
    if (ISNAN (x) || x + x == x)
      {
        *expptr = 0;
        return x;
      }
  
    sign = 0;
    if (x < 0)
      {
        x = - x;
        sign = -1;
      }
  
    BEGIN_ROUNDING ();
  
    {
      /* Since the exponent is an 'int', it fits in 64 bits.  Therefore the
         loops are executed no more than 64 times.  */
      DOUBLE pow2[64]; /* pow2[i] = 2^2^i */
      DOUBLE powh[64]; /* powh[i] = 2^-2^i */
      int i;
  
      exponent = 0;
      if (x >= L_(1.0))
        {
          /* A positive exponent.  */
          DOUBLE pow2_i; /* = pow2[i] */
          DOUBLE powh_i; /* = powh[i] */
  
          /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
             x * 2^exponent = argument, x >= 1.0.  */
          for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
               ;
               i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
            {
              if (x >= pow2_i)
                {
                  exponent += (1 << i);
                  x *= powh_i;
                }
              else
                break;
  
              pow2[i] = pow2_i;
              powh[i] = powh_i;
            }
          /* Avoid making x too small, as it could become a denormalized
             number and thus lose precision.  */
          while (i > 0 && x < pow2[i - 1])
            {
              i--;
              powh_i = powh[i];
            }
          exponent += (1 << i);
          x *= powh_i;
          /* Here 2^-2^i <= x < 1.0.  */
        }
      else
        {
          /* A negative or zero exponent.  */
          DOUBLE pow2_i; /* = pow2[i] */
          DOUBLE powh_i; /* = powh[i] */
  
          /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
             x * 2^exponent = argument, x < 1.0.  */
          for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
               ;
               i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
            {
              if (x < powh_i)
                {
                  exponent -= (1 << i);
                  x *= pow2_i;
                }
              else
                break;
  
              pow2[i] = pow2_i;
              powh[i] = powh_i;
            }
          /* Here 2^-2^i <= x < 1.0.  */
        }
  
      /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0.  */
      while (i > 0)
        {
          i--;
          if (x < powh[i])
            {
              exponent -= (1 << i);
              x *= pow2[i];
            }
        }
      /* Here 0.5 <= x < 1.0.  */
    }
  
    if (sign < 0)
      x = - x;
  
    END_ROUNDING ();
  
    *expptr = exponent;
    return x;
  }
  

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