sysdeps/ieee754/ldbl-128/ldbl2mpn.c

   1 /* Copyright (C) 1995-2015 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    <http://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 quad-precision format to a
  27    multi-precision integer representing the significand scaled up by its
  28    number of bits (113 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.mantissa3; /* Low-order 32 bits of fraction.  */
  44   res_ptr[1] = u.ieee.mantissa2;
  45   res_ptr[2] = u.ieee.mantissa1;
  46   res_ptr[3] = u.ieee.mantissa0; /* High-order 32 bits.  */
  47   #define N 4
  48 #elif BITS_PER_MP_LIMB == 64
  49   /* Hopefully the compiler will combine the two bitfield extracts
  50      and this composition into just the original quadword extract.  */
  51   res_ptr[0] = ((mp_limb_t) u.ieee.mantissa2 << 32) | u.ieee.mantissa3;
  52   res_ptr[1] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  53   #define N 2
  54 #else
  55   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  56 #endif
  57 /* The format does not fill the last limb.  There are some zeros.  */
  58 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
  59                            - (LDBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
  60
  61   if (u.ieee.exponent == 0)
  62     {
  63       /* A biased exponent of zero is a special case.
  64          Either it is a zero or it is a denormal number.  */
  65       if (res_ptr[0] == 0 && res_ptr[1] == 0
  66           && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4.  */
  67         /* It's zero.  */
  68         *expt = 0;
  69       else
  70         {
  71           /* It is a denormal number, meaning it has no implicit leading
  72              one bit, and its exponent is in fact the format minimum.  */
  73           int cnt;
  74
  75 #if N == 2
  76           if (res_ptr[N - 1] != 0)
  77             {
  78               count_leading_zeros (cnt, res_ptr[N - 1]);
  79               cnt -= NUM_LEADING_ZEROS;
  80               res_ptr[N - 1] = res_ptr[N - 1] << cnt
  81                                | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
  82               res_ptr[0] <<= cnt;
  83               *expt = LDBL_MIN_EXP - 1 - cnt;
  84             }
  85           else
  86             {
  87               count_leading_zeros (cnt, res_ptr[0]);
  88               if (cnt >= NUM_LEADING_ZEROS)
  89                 {
  90                   res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
  91                   res_ptr[0] = 0;
  92                 }
  93               else
  94                 {
  95                   res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
  96                   res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
  97                 }
  98               *expt = LDBL_MIN_EXP - 1
  99                 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
 100             }
 101 #else
 102           int j, k, l;
 103
 104           for (j = N - 1; j > 0; j--)
 105             if (res_ptr[j] != 0)
 106               break;
 107
 108           count_leading_zeros (cnt, res_ptr[j]);
 109           cnt -= NUM_LEADING_ZEROS;
 110           l = N - 1 - j;
 111           if (cnt < 0)
 112             {
 113               cnt += BITS_PER_MP_LIMB;
 114               l--;
 115             }
 116           if (!cnt)
 117             for (k = N - 1; k >= l; k--)
 118               res_ptr[k] = res_ptr[k-l];
 119           else
 120             {
 121               for (k = N - 1; k > l; k--)
 122                 res_ptr[k] = res_ptr[k-l] << cnt
 123                              | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
 124               res_ptr[k--] = res_ptr[0] << cnt;
 125             }
 126
 127           for (; k >= 0; k--)
 128             res_ptr[k] = 0;
 129           *expt = LDBL_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
 130 #endif
 131         }
 132     }
 133   else
 134     /* Add the implicit leading one bit for a normalized number.  */
 135     res_ptr[N - 1] |= (mp_limb_t) 1 << (LDBL_MANT_DIG - 1
 136                                         - ((N - 1) * BITS_PER_MP_LIMB));
 137
 138   return N;
 139 }