libquadmath/printf/flt1282mpn.c

   1 /* Copyright (C) 1995-2013 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <float.h>
  20 #include <math.h>
  21 #include <stdlib.h>
  22 #include "gmp-impl.h"
  23
  24 /* Convert a `__float128' in IEEE854 quad-precision format to a
  25    multi-precision integer representing the significand scaled up by its
  26    number of bits (113 for long double) and an integral power of two
  27    (MPN frexpl). */
  28
  29 mp_size_t
  30 mpn_extract_flt128 (mp_ptr res_ptr, mp_size_t size,
  31                       int *expt, int *is_neg,
  32                       __float128 value)
  33 {
  34   ieee854_float128 u;
  35   u.value = value;
  36
  37   *is_neg = u.ieee.negative;
  38   *expt = (int) u.ieee.exponent - IEEE854_FLOAT128_BIAS;
  39
  40 #if BITS_PER_MP_LIMB == 32
  41   res_ptr[0] = u.ieee.mant_low; /* Low-order 32 bits of fraction.  */
  42   res_ptr[1] = (u.ieee.mant_low >> 32);
  43   res_ptr[2] = u.ieee.mant_high;
  44   res_ptr[3] = (u.ieee.mant_high >> 32); /* High-order 32 bits.  */
  45   #define N 4
  46 #elif BITS_PER_MP_LIMB == 64
  47   res_ptr[0] = u.ieee.mant_low;
  48   res_ptr[1] = u.ieee.mant_high;
  49   #define N 2
  50 #else
  51   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  52 #endif
  53 /* The format does not fill the last limb.  There are some zeros.  */
  54 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
  55                            - (FLT128_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
  56
  57   if (u.ieee.exponent == 0)
  58     {
  59       /* A biased exponent of zero is a special case.
  60          Either it is a zero or it is a denormal number.  */
  61       if (res_ptr[0] == 0 && res_ptr[1] == 0
  62           && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4.  */
  63         /* It's zero.  */
  64         *expt = 0;
  65       else
  66         {
  67           /* It is a denormal number, meaning it has no implicit leading
  68              one bit, and its exponent is in fact the format minimum.  */
  69           int cnt;
  70
  71 #if N == 2
  72           if (res_ptr[N - 1] != 0)
  73             {
  74               count_leading_zeros (cnt, res_ptr[N - 1]);
  75               cnt -= NUM_LEADING_ZEROS;
  76               res_ptr[N - 1] = res_ptr[N - 1] << cnt
  77                                | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
  78               res_ptr[0] <<= cnt;
  79               *expt = FLT128_MIN_EXP - 1 - cnt;
  80             }
  81           else
  82             {
  83               count_leading_zeros (cnt, res_ptr[0]);
  84               if (cnt >= NUM_LEADING_ZEROS)
  85                 {
  86                   res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
  87                   res_ptr[0] = 0;
  88                 }
  89               else
  90                 {
  91                   res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
  92                   res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
  93                 }
  94               *expt = FLT128_MIN_EXP - 1
  95                 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
  96             }
  97 #else
  98           int j, k, l;
  99
 100           for (j = N - 1; j > 0; j--)
 101             if (res_ptr[j] != 0)
 102               break;
 103
 104           count_leading_zeros (cnt, res_ptr[j]);
 105           cnt -= NUM_LEADING_ZEROS;
 106           l = N - 1 - j;
 107           if (cnt < 0)
 108             {
 109               cnt += BITS_PER_MP_LIMB;
 110               l--;
 111             }
 112           if (!cnt)
 113             for (k = N - 1; k >= l; k--)
 114               res_ptr[k] = res_ptr[k-l];
 115           else
 116             {
 117               for (k = N - 1; k > l; k--)
 118                 res_ptr[k] = res_ptr[k-l] << cnt
 119                              | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
 120               res_ptr[k--] = res_ptr[0] << cnt;
 121             }
 122
 123           for (; k >= 0; k--)
 124             res_ptr[k] = 0;
 125           *expt = FLT128_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
 126 #endif
 127         }
 128     }
 129   else
 130     /* Add the implicit leading one bit for a normalized number.  */
 131     res_ptr[N - 1] |= (mp_limb_t) 1 << (FLT128_MANT_DIG - 1
 132                                         - ((N - 1) * BITS_PER_MP_LIMB));
 133
 134   return N;
 135 }