sysdeps/ieee754/ldbl-128/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 <math_private.h>
  25 #include <stdlib.h>
  26
  27 /* Convert a `long double' in IEEE854 quad-precision format to a
  28    multi-precision integer representing the significand scaled up by its
  29    number of bits (113 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                            _Float128 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.mantissa3; /* Low-order 32 bits of fraction.  */
  45   res_ptr[1] = u.ieee.mantissa2;
  46   res_ptr[2] = u.ieee.mantissa1;
  47   res_ptr[3] = u.ieee.mantissa0; /* High-order 32 bits.  */
  48   #define N 4
  49 #elif BITS_PER_MP_LIMB == 64
  50   /* Hopefully the compiler will combine the two bitfield extracts
  51      and this composition into just the original quadword extract.  */
  52   res_ptr[0] = ((mp_limb_t) u.ieee.mantissa2 << 32) | u.ieee.mantissa3;
  53   res_ptr[1] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
  54   #define N 2
  55 #else
  56   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  57 #endif
  58 /* The format does not fill the last limb.  There are some zeros.  */
  59 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
  60                            - (LDBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
  61
  62   if (u.ieee.exponent == 0)
  63     {
  64       /* A biased exponent of zero is a special case.
  65          Either it is a zero or it is a denormal number.  */
  66       if (res_ptr[0] == 0 && res_ptr[1] == 0
  67           && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4.  */
  68         /* It's zero.  */
  69         *expt = 0;
  70       else
  71         {
  72           /* It is a denormal number, meaning it has no implicit leading
  73              one bit, and its exponent is in fact the format minimum.  */
  74           int cnt;
  75
  76 #if N == 2
  77           if (res_ptr[N - 1] != 0)
  78             {
  79               count_leading_zeros (cnt, res_ptr[N - 1]);
  80               cnt -= NUM_LEADING_ZEROS;
  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               *expt = LDBL_MIN_EXP - 1 - cnt;
  85             }
  86           else
  87             {
  88               count_leading_zeros (cnt, res_ptr[0]);
  89               if (cnt >= NUM_LEADING_ZEROS)
  90                 {
  91                   res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
  92                   res_ptr[0] = 0;
  93                 }
  94               else
  95                 {
  96                   res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
  97                   res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
  98                 }
  99               *expt = LDBL_MIN_EXP - 1
 100                 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
 101             }
 102 #else
 103           int j, k, l;
 104
 105           for (j = N - 1; j > 0; j--)
 106             if (res_ptr[j] != 0)
 107               break;
 108
 109           count_leading_zeros (cnt, res_ptr[j]);
 110           cnt -= NUM_LEADING_ZEROS;
 111           l = N - 1 - j;
 112           if (cnt < 0)
 113             {
 114               cnt += BITS_PER_MP_LIMB;
 115               l--;
 116             }
 117           if (!cnt)
 118             for (k = N - 1; k >= l; k--)
 119               res_ptr[k] = res_ptr[k-l];
 120           else
 121             {
 122               for (k = N - 1; k > l; k--)
 123                 res_ptr[k] = res_ptr[k-l] << cnt
 124                              | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
 125               res_ptr[k--] = res_ptr[0] << cnt;
 126             }
 127
 128           for (; k >= 0; k--)
 129             res_ptr[k] = 0;
 130           *expt = LDBL_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
 131 #endif
 132         }
 133     }
 134   else
 135     /* Add the implicit leading one bit for a normalized number.  */
 136     res_ptr[N - 1] |= (mp_limb_t) 1 << (LDBL_MANT_DIG - 1
 137                                         - ((N - 1) * BITS_PER_MP_LIMB));
 138
 139   return N;
 140 }