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glibc  2.9
Defines | Functions
ldbl2mpn.c File Reference
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#include <ieee754.h>
#include <float.h>
#include <math.h>
#include <stdlib.h>

Go to the source code of this file.

Defines

#define NUM_LEADING_ZEROS

Functions

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

Define Documentation

Value:

Function Documentation

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

Definition at line 34 of file ldbl2mpn.c.

{
  union ibm_extended_long_double u;
  unsigned long long hi, lo;
  int ediff;
  u.d = value;

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

  lo = ((long long) u.ieee.mantissa2 << 32) | u.ieee.mantissa3;
  hi = ((long long) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  /* If the lower double is not a denomal or zero then set the hidden
     53rd bit.  */
  if (u.ieee.exponent2 > 0)
    {
      lo |= 1LL << 52;

      /* The lower double is normalized separately from the upper.  We may
        need to adjust the lower manitissa to reflect this.  */
      ediff = u.ieee.exponent - u.ieee.exponent2;
      if (ediff > 53)
       lo = lo >> (ediff-53);
    }
  /* The high double may be rounded and the low double reflects the
     difference between the long double and the rounded high double
     value.  This is indicated by a differnce between the signs of the
     high and low doubles.  */
  if ((u.ieee.negative != u.ieee.negative2)
      && ((u.ieee.exponent2 != 0) && (lo != 0L)))
    {
      lo = (1ULL << 53) - lo;
      if (hi == 0LL)
       {
         /* we have a borrow from the hidden bit, so shift left 1.  */
         hi = 0x0ffffffffffffeLL | (lo >> 51);
         lo = 0x1fffffffffffffLL & (lo << 1);
         (*expt)--;
       }
      else
       hi--;
    }
#if BITS_PER_MP_LIMB == 32
  /* Combine the mantissas to be contiguous.  */
  res_ptr[0] = lo;
  res_ptr[1] = (hi << (53 - 32)) | (lo >> 32);
  res_ptr[2] = hi >> 11;
  res_ptr[3] = hi >> (32 + 11);
  #define N 4
#elif BITS_PER_MP_LIMB == 64
  /* Combine the two mantissas to be contiguous.  */
  res_ptr[0] = (hi << 53) | lo;
  res_ptr[1] = hi >> 11;
  #define N 2
#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 \
                        - (LDBL_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[1] == 0
         && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4.  */
       /* 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 N == 2
         if (res_ptr[N - 1] != 0)
           {
             count_leading_zeros (cnt, res_ptr[N - 1]);
             cnt -= NUM_LEADING_ZEROS;
             res_ptr[N - 1] = res_ptr[N - 1] << cnt
                            | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
             res_ptr[0] <<= cnt;
             *expt = LDBL_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 = LDBL_MIN_EXP - 1
              - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
           }
#else
         int j, k, l;

         for (j = N - 1; j > 0; j--)
           if (res_ptr[j] != 0)
             break;

         count_leading_zeros (cnt, res_ptr[j]);
         cnt -= NUM_LEADING_ZEROS;
         l = N - 1 - j;
         if (cnt < 0)
           {
             cnt += BITS_PER_MP_LIMB;
             l--;
           }
         if (!cnt)
           for (k = N - 1; k >= l; k--)
             res_ptr[k] = res_ptr[k-l];
         else
           {
             for (k = N - 1; k > l; k--)
              res_ptr[k] = res_ptr[k-l] << cnt
                          | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
             res_ptr[k--] = res_ptr[0] << cnt;
           }

         for (; k >= 0; k--)
           res_ptr[k] = 0;
         *expt = LDBL_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
#endif
       }
    }
  else
    /* Add the implicit leading one bit for a normalized number.  */
    res_ptr[N - 1] |= (mp_limb_t) 1 << (LDBL_MANT_DIG - 1
                                   - ((N - 1) * BITS_PER_MP_LIMB));

  return N;
}