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glibc  2.9
Defines | Functions
dbl2mpn.c File Reference
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#include <ieee754.h>
#include <float.h>
#include <stdlib.h>

Go to the source code of this file.

Defines

#define NUM_LEADING_ZEROS

Functions

mp_size_t __mpn_extract_double (mp_ptr res_ptr, mp_size_t size, int *expt, int *is_neg, double value)

Define Documentation

Value:

Function Documentation

mp_size_t __mpn_extract_double ( mp_ptr  res_ptr,
mp_size_t  size,
int expt,
int is_neg,
double  value 
)

Definition at line 31 of file dbl2mpn.c.

{
  union ieee754_double u;
  u.d = value;

  *is_neg = u.ieee.negative;
  *expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS;

#if BITS_PER_MP_LIMB == 32
  res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
  res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits.  */
  #define N 2
#elif BITS_PER_MP_LIMB == 64
  /* Hopefully the compiler will combine the two bitfield extracts
     and this composition into just the original quadword extract.  */
  res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  #define N 1
#else
  #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
#endif
/* The format does not fill the last limb.  There are some zeros.  */
#define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
                        - (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))

  if (u.ieee.exponent == 0)
    {
      /* A biased exponent of zero is a special case.
        Either it is a zero or it is a denormal number.  */
      if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
       /* It's zero.  */
       *expt = 0;
      else
       {
          /* It is a denormal number, meaning it has no implicit leading
            one bit, and its exponent is in fact the format minimum.  */
         int cnt;

         if (res_ptr[N - 1] != 0)
           {
             count_leading_zeros (cnt, res_ptr[N - 1]);
             cnt -= NUM_LEADING_ZEROS;
#if N == 2
             res_ptr[N - 1] = res_ptr[1] << cnt
                            | (N - 1)
                              * (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
             res_ptr[0] <<= cnt;
#else
             res_ptr[N - 1] <<= cnt;
#endif
             *expt = DBL_MIN_EXP - 1 - cnt;
           }
         else
           {
             count_leading_zeros (cnt, res_ptr[0]);
             if (cnt >= NUM_LEADING_ZEROS)
              {
                res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
                res_ptr[0] = 0;
              }
             else
              {
                res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
                res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
              }
             *expt = DBL_MIN_EXP - 1
                    - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
           }
       }
    }
  else
    /* Add the implicit leading one bit for a normalized number.  */
    res_ptr[N - 1] |= (mp_limb_t) 1 << (DBL_MANT_DIG - 1
                                   - ((N - 1) * BITS_PER_MP_LIMB));

  return N;
}

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