sysdeps/ieee754/ldbl-96/ldbl2mpn.c

   1 /* Copyright (C) 1995,1996,1997,1998,2002,2003 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 "gmp.h"
  20 #include "gmp-impl.h"
  21 #include "longlong.h"
  22 #include <ieee754.h>
  23 #include <float.h>
  24 #include <math.h>
  25 #include <stdlib.h>
  26
  27 /* Convert a `long double' in IEEE854 standard double-precision format to a
  28    multi-precision integer representing the significand scaled up by its
  29    number of bits (64 for long double) and an integral power of two
  30    (MPN frexpl). */
  31
  32 mp_size_t
  33 __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
  34                            int *expt, int *is_neg,
  35                            long double value)
  36 {
  37   union ieee854_long_double u;
  38   u.d = value;
  39
  40   *is_neg = u.ieee.negative;
  41   *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
  42
  43 #if BITS_PER_MP_LIMB == 32
  44   res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
  45   res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits.  */
  46   #define N 2
  47 #elif BITS_PER_MP_LIMB == 64
  48   /* Hopefully the compiler will combine the two bitfield extracts
  49      and this composition into just the original quadword extract.  */
  50   res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  51   #define N 1
  52 #else
  53   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  54 #endif
  55
  56   if (u.ieee.exponent == 0)
  57     {
  58       /* A biased exponent of zero is a special case.
  59          Either it is a zero or it is a denormal number.  */
  60       if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
  61         /* It's zero.  */
  62         *expt = 0;
  63       else
  64         {
  65           /* It is a denormal number, meaning it has no implicit leading
  66              one bit, and its exponent is in fact the format minimum.  */
  67           int cnt;
  68
  69           if (res_ptr[N - 1] != 0)
  70             {
  71               count_leading_zeros (cnt, res_ptr[N - 1]);
  72               if (cnt != 0)
  73                 {
  74 #if N == 2
  75                   res_ptr[N - 1] = res_ptr[N - 1] << cnt
  76                                    | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
  77                   res_ptr[0] <<= cnt;
  78 #else
  79                   res_ptr[N - 1] <<= cnt;
  80 #endif
  81                 }
  82               *expt = LDBL_MIN_EXP - 1 - cnt;
  83             }
  84           else
  85             {
  86               count_leading_zeros (cnt, res_ptr[0]);
  87               res_ptr[N - 1] = res_ptr[0] << cnt;
  88               res_ptr[0] = 0;
  89               *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
  90             }
  91         }
  92     }
  93
  94   return N;
  95 }