sysdeps/ieee754/ldbl-96/ldbl2mpn.c

   1 /* Copyright (C) 1995-2024 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    <https://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 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           if (res_ptr[N - 1] != 0)
  69             {
  70               count_leading_zeros (cnt, res_ptr[N - 1]);
  71               if (cnt != 0)
  72                 {
  73 #if N == 2
  74                   res_ptr[N - 1] = res_ptr[N - 1] << cnt
  75                                    | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
  76                   res_ptr[0] <<= cnt;
  77 #else
  78                   res_ptr[N - 1] <<= cnt;
  79 #endif
  80                 }
  81               *expt = LDBL_MIN_EXP - 1 - cnt;
  82             }
  83           else
  84             {
  85               count_leading_zeros (cnt, res_ptr[0]);
  86               res_ptr[N - 1] = res_ptr[0] << cnt;
  87               res_ptr[0] = 0;
  88               *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
  89             }
  90         }
  91     }
  92
  93   return N;
  94 }