1  /* Copyright (C) 1995-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #include "gmp.h"
      19  #include "gmp-impl.h"
      20  #include "longlong.h"
      21  #include <ieee754.h>
      22  #include <float.h>
      23  #include <math.h>
      24  #include <stdlib.h>
      25  
      26  /* Convert a `long double' in IEEE854 standard double-precision format to a
      27     multi-precision integer representing the significand scaled up by its
      28     number of bits (64 for long double) and an integral power of two
      29     (MPN frexpl). */
      30  
      31  mp_size_t
      32  __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
      33  			   int *expt, int *is_neg,
      34  			   long double value)
      35  {
      36    union ieee854_long_double u;
      37    u.d = value;
      38  
      39    *is_neg = u.ieee.negative;
      40    *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
      41  
      42  #if BITS_PER_MP_LIMB == 32
      43    res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
      44    res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits.  */
      45    #define N 2
      46  #elif BITS_PER_MP_LIMB == 64
      47    /* Hopefully the compiler will combine the two bitfield extracts
      48       and this composition into just the original quadword extract.  */
      49    res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
      50    #define N 1
      51  #else
      52    #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
      53  #endif
      54  
      55    if (u.ieee.exponent == 0)
      56      {
      57        /* A biased exponent of zero is a special case.
      58  	 Either it is a zero or it is a denormal number.  */
      59        if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
      60  	/* It's zero.  */
      61  	*expt = 0;
      62        else
      63  	{
      64            /* It is a denormal number, meaning it has no implicit leading
      65  	     one bit, and its exponent is in fact the format minimum.  */
      66  	  int cnt;
      67  
      68  	  if (res_ptr[N - 1] != 0)
      69  	    {
      70  	      count_leading_zeros (cnt, res_ptr[N - 1]);
      71  	      if (cnt != 0)
      72  		{
      73  #if N == 2
      74  	          res_ptr[N - 1] = res_ptr[N - 1] << cnt
      75  			           | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
      76  	          res_ptr[0] <<= cnt;
      77  #else
      78  	          res_ptr[N - 1] <<= cnt;
      79  #endif
      80  		}
      81  	      *expt = LDBL_MIN_EXP - 1 - cnt;
      82  	    }
      83  	  else
      84  	    {
      85  	      count_leading_zeros (cnt, res_ptr[0]);
      86  	      res_ptr[N - 1] = res_ptr[0] << cnt;
      87  	      res_ptr[0] = 0;
      88  	      *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
      89  	    }
      90  	}
      91      }
      92  
      93    return N;
      94  }