source/libs/mpfr/mpfr-3.1.3/src/eq.c

   1 /* mpfr_eq -- Compare two floats up to a specified bit #.
   2
   3 Copyright 1999, 2001, 2003-2004, 2006-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  22
  23
  24 #include "mpfr-impl.h"
  25
  26 /* return non-zero if the first n_bits bits of u, v are equal,
  27    0 otherwise */
  28 int
  29 mpfr_eq (mpfr_srcptr u, mpfr_srcptr v, unsigned long int n_bits)
  30 {
  31   mpfr_limb_srcptr up, vp;
  32   mp_size_t usize, vsize, size, i;
  33   mpfr_exp_t uexp, vexp;
  34   int k;
  35
  36   if (MPFR_ARE_SINGULAR(u, v))
  37     {
  38       if (MPFR_IS_NAN(u) || MPFR_IS_NAN(v))
  39         return 0; /* non equal */
  40       else if (MPFR_IS_INF(u) && MPFR_IS_INF(v))
  41         return (MPFR_SIGN(u) == MPFR_SIGN(v));
  42       else if (MPFR_IS_ZERO(u) && MPFR_IS_ZERO(v))
  43         return 1;
  44       else
  45         return 0;
  46     }
  47
  48   /* 1. Are the signs different?  */
  49   if (MPFR_SIGN(u) != MPFR_SIGN(v))
  50     return 0;
  51
  52   uexp = MPFR_GET_EXP (u);
  53   vexp = MPFR_GET_EXP (v);
  54
  55   /* 2. Are the exponents different?  */
  56   if (uexp != vexp)
  57     return 0; /* no bit agree */
  58
  59   usize = MPFR_LIMB_SIZE (u);
  60   vsize = MPFR_LIMB_SIZE (v);
  61
  62   if (vsize > usize) /* exchange u and v */
  63     {
  64       up = MPFR_MANT(v);
  65       vp = MPFR_MANT(u);
  66       size = vsize;
  67       vsize = usize;
  68       usize = size;
  69     }
  70   else
  71     {
  72       up = MPFR_MANT(u);
  73       vp = MPFR_MANT(v);
  74     }
  75
  76   /* now usize >= vsize */
  77   MPFR_ASSERTD(usize >= vsize);
  78
  79   if (usize > vsize)
  80     {
  81       if ((unsigned long) vsize * GMP_NUMB_BITS < n_bits)
  82         {
  83           /* check if low min(PREC(u), n_bits) - (vsize * GMP_NUMB_BITS)
  84              bits from u are non-zero */
  85           unsigned long remains = n_bits - (vsize * GMP_NUMB_BITS);
  86           k = usize - vsize - 1;
  87           while (k >= 0 && remains >= GMP_NUMB_BITS && !up[k])
  88             {
  89               k--;
  90               remains -= GMP_NUMB_BITS;
  91             }
  92           /* now either k < 0: all low bits from u are zero
  93                  or remains < GMP_NUMB_BITS: check high bits from up[k]
  94                  or up[k] <> 0: different */
  95           if (k >= 0 && (((remains < GMP_NUMB_BITS) &&
  96                           (up[k] >> (GMP_NUMB_BITS - remains))) ||
  97                          (remains >= GMP_NUMB_BITS && up[k])))
  98             return 0;           /* surely too different */
  99         }
 100       size = vsize;
 101     }
 102   else
 103     {
 104       size = usize;
 105     }
 106
 107   /* now size = min (usize, vsize) */
 108
 109   /* If size is too large wrt n_bits, reduce it to look only at the
 110      high n_bits bits.
 111      Otherwise, if n_bits > size * GMP_NUMB_BITS, reduce n_bits to
 112      size * GMP_NUMB_BITS, since the extra low bits of one of the
 113      operands have already been check above. */
 114   if ((unsigned long) size > 1 + (n_bits - 1) / GMP_NUMB_BITS)
 115     size = 1 + (n_bits - 1) / GMP_NUMB_BITS;
 116   else if (n_bits > (unsigned long) size * GMP_NUMB_BITS)
 117     n_bits = size * GMP_NUMB_BITS;
 118
 119   up += usize - size;
 120   vp += vsize - size;
 121
 122   for (i = size - 1; i > 0 && n_bits >= GMP_NUMB_BITS; i--)
 123     {
 124       if (up[i] != vp[i])
 125         return 0;
 126       n_bits -= GMP_NUMB_BITS;
 127     }
 128
 129   /* now either i=0 or n_bits<GMP_NUMB_BITS */
 130
 131   /* since n_bits <= size * GMP_NUMB_BITS before the above for-loop,
 132      we have the invariant n_bits <= (i+1) * GMP_NUMB_BITS, thus
 133      we always have n_bits <= GMP_NUMB_BITS here */
 134   MPFR_ASSERTD(n_bits <= GMP_NUMB_BITS);
 135
 136   if (n_bits & (GMP_NUMB_BITS - 1))
 137     return (up[i] >> (GMP_NUMB_BITS - (n_bits & (GMP_NUMB_BITS - 1))) ==
 138             vp[i] >> (GMP_NUMB_BITS - (n_bits & (GMP_NUMB_BITS - 1))));
 139   else
 140     return (up[i] == vp[i]);
 141 }