sysdeps/ieee754/ldbl-128/ldbl2mpn.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2002,2003
   2         Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include "gmp.h"
  21 #include "gmp-impl.h"
  22 #include "longlong.h"
  23 #include <ieee754.h>
  24 #include <float.h>
  25 #include <math.h>
  26 #include <stdlib.h>
  27
  28 /* Convert a `long double' in IEEE854 quad-precision format to a
  29    multi-precision integer representing the significand scaled up by its
  30    number of bits (113 for long double) and an integral power of two
  31    (MPN frexpl). */
  32
  33 mp_size_t
  34 __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
  35                            int *expt, int *is_neg,
  36                            long double value)
  37 {
  38   union ieee854_long_double u;
  39   u.d = value;
  40
  41   *is_neg = u.ieee.negative;
  42   *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
  43
  44 #if BITS_PER_MP_LIMB == 32
  45   res_ptr[0] = u.ieee.mantissa3; /* Low-order 32 bits of fraction.  */
  46   res_ptr[1] = u.ieee.mantissa2;
  47   res_ptr[2] = u.ieee.mantissa1;
  48   res_ptr[3] = u.ieee.mantissa0; /* High-order 32 bits.  */
  49   #define N 4
  50 #elif BITS_PER_MP_LIMB == 64
  51   /* Hopefully the compiler will combine the two bitfield extracts
  52      and this composition into just the original quadword extract.  */
  53   res_ptr[0] = ((mp_limb_t) u.ieee.mantissa2 << 32) | u.ieee.mantissa3;
  54   res_ptr[1] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  55   #define N 2
  56 #else
  57   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  58 #endif
  59 /* The format does not fill the last limb.  There are some zeros.  */
  60 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
  61                            - (LDBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
  62
  63   if (u.ieee.exponent == 0)
  64     {
  65       /* A biased exponent of zero is a special case.
  66          Either it is a zero or it is a denormal number.  */
  67       if (res_ptr[0] == 0 && res_ptr[1] == 0
  68           && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4.  */
  69         /* It's zero.  */
  70         *expt = 0;
  71       else
  72         {
  73           /* It is a denormal number, meaning it has no implicit leading
  74              one bit, and its exponent is in fact the format minimum.  */
  75           int cnt;
  76
  77 #if N == 2
  78           if (res_ptr[N - 1] != 0)
  79             {
  80               count_leading_zeros (cnt, res_ptr[N - 1]);
  81               cnt -= NUM_LEADING_ZEROS;
  82               res_ptr[N - 1] = res_ptr[N - 1] << cnt
  83                                | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
  84               res_ptr[0] <<= cnt;
  85               *expt = LDBL_MIN_EXP - 1 - cnt;
  86             }
  87           else
  88             {
  89               count_leading_zeros (cnt, res_ptr[0]);
  90               if (cnt >= NUM_LEADING_ZEROS)
  91                 {
  92                   res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
  93                   res_ptr[0] = 0;
  94                 }
  95               else
  96                 {
  97                   res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
  98                   res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
  99                 }
 100               *expt = LDBL_MIN_EXP - 1
 101                 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
 102             }
 103 #else
 104           int j, k, l;
 105
 106           for (j = N - 1; j > 0; j--)
 107             if (res_ptr[j] != 0)
 108               break;
 109
 110           count_leading_zeros (cnt, res_ptr[j]);
 111           cnt -= NUM_LEADING_ZEROS;
 112           l = N - 1 - j;
 113           if (cnt < 0)
 114             {
 115               cnt += BITS_PER_MP_LIMB;
 116               l--;
 117             }
 118           if (!cnt)
 119             for (k = N - 1; k >= l; k--)
 120               res_ptr[k] = res_ptr[k-l];
 121           else
 122             {
 123               for (k = N - 1; k > l; k--)
 124                 res_ptr[k] = res_ptr[k-l] << cnt
 125                              | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
 126               res_ptr[k--] = res_ptr[0] << cnt;
 127             }
 128
 129           for (; k >= 0; k--)
 130             res_ptr[k] = 0;
 131           *expt = LDBL_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
 132 #endif
 133         }
 134     }
 135   else
 136     /* Add the implicit leading one bit for a normalized number.  */
 137     res_ptr[N - 1] |= (mp_limb_t) 1 << (LDBL_MANT_DIG - 1
 138                                         - ((N - 1) * BITS_PER_MP_LIMB));
 139
 140   return N;
 141 }