sysdeps/i386/ldbl2mpn.c

   1 /* Copyright (C) 1995, 1996, 1997, 2000, 2007 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 <stdlib.h>
  25
  26 /* Convert a `long double' in IEEE854 standard double-precision format to a
  27    multi-precision integer representing the significand scaled up by its
  28    number of bits (64 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.mantissa1; /* Low-order 32 bits of fraction.  */
  44   res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits.  */
  45   #define N 2
  46 #elif BITS_PER_MP_LIMB == 64
  47   /* Hopefully the compiler will combine the two bitfield extracts
  48      and this composition into just the original quadword extract.  */
  49   res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  50   #define N 1
  51 #else
  52   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  53 #endif
  54
  55   if (u.ieee.exponent == 0)
  56     {
  57       /* A biased exponent of zero is a special case.
  58          Either it is a zero or it is a denormal number.  */
  59       if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
  60         /* It's zero.  */
  61         *expt = 0;
  62       else
  63         {
  64           /* It is a denormal number, meaning it has no implicit leading
  65              one bit, and its exponent is in fact the format minimum.  */
  66           int cnt;
  67
  68           /* One problem with Intel's 80-bit format is that the explicit
  69              leading one in the normalized representation has to be zero
  70              for denormalized number.  If it is one, the number is according
  71              to Intel's specification an invalid number.  We make the
  72              representation unique by explicitly clearing this bit.  */
  73           res_ptr[N - 1] &= ~(1L << ((LDBL_MANT_DIG - 1) % BITS_PER_MP_LIMB));
  74
  75           if (res_ptr[N - 1] != 0)
  76             {
  77               count_leading_zeros (cnt, res_ptr[N - 1]);
  78               if (cnt != 0)
  79                 {
  80 #if N == 2
  81                   res_ptr[N - 1] = res_ptr[N - 1] << cnt
  82                                    | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
  83                   res_ptr[0] <<= cnt;
  84 #else
  85                   res_ptr[N - 1] <<= cnt;
  86 #endif
  87                 }
  88               *expt = LDBL_MIN_EXP - 1 - cnt;
  89             }
  90           else if (res_ptr[0] != 0)
  91             {
  92               count_leading_zeros (cnt, res_ptr[0]);
  93               res_ptr[N - 1] = res_ptr[0] << cnt;
  94               res_ptr[0] = 0;
  95               *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
  96             }
  97           else
  98             {
  99               /* This is the special case of the pseudo denormal number
 100                  with only the implicit leading bit set.  The value is
 101                  in fact a normal number and so we have to treat this
 102                  case differently.  */
 103 #if N == 2
 104               res_ptr[N - 1] = 0x80000000ul;
 105 #else
 106               res_ptr[0] = 0x8000000000000000ul;
 107 #endif
 108               *expt = LDBL_MIN_EXP - 1;
 109             }
 110         }
 111     }
 112   else if (u.ieee.exponent < 0x7fff
 113 #if N == 2
 114            && res_ptr[0] == 0
 115 #endif
 116            && res_ptr[N - 1] == 0)
 117     /* Pseudo zero.  */
 118     *expt = 0;
 119
 120   return N;
 121 }