contrib/gmp/mpf/eq.c

   1 /* mpf_eq -- Compare two floats up to a specified bit #.
   2
   3 Copyright 1993, 1995, 1996, 2001, 2002, 2008, 2009 Free Software Foundation,
   4 Inc.
   5
   6 This file is part of the GNU MP Library.
   7
   8 The GNU MP 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 MP 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 MP Library.  If not, see http://www.gnu.org/licenses/.  */
  20
  21 #include "gmp.h"
  22 #include "gmp-impl.h"
  23 #include "longlong.h"
  24
  25 int
  26 mpf_eq (mpf_srcptr u, mpf_srcptr v, mp_bitcnt_t n_bits)
  27 {
  28   mp_srcptr up, vp, p;
  29   mp_size_t usize, vsize, minsize, maxsize, n_limbs, i, size;
  30   mp_exp_t uexp, vexp;
  31   mp_limb_t diff;
  32   int cnt;
  33
  34   uexp = u->_mp_exp;
  35   vexp = v->_mp_exp;
  36
  37   usize = u->_mp_size;
  38   vsize = v->_mp_size;
  39
  40   /* 1. Are the signs different?  */
  41   if ((usize ^ vsize) >= 0)
  42     {
  43       /* U and V are both non-negative or both negative.  */
  44       if (usize == 0)
  45         return vsize == 0;
  46       if (vsize == 0)
  47         return 0;
  48
  49       /* Fall out.  */
  50     }
  51   else
  52     {
  53       /* Either U or V is negative, but not both.  */
  54       return 0;
  55     }
  56
  57   /* U and V have the same sign and are both non-zero.  */
  58
  59   /* 2. Are the exponents different?  */
  60   if (uexp != vexp)
  61     return 0;
  62
  63   usize = ABS (usize);
  64   vsize = ABS (vsize);
  65
  66   up = u->_mp_d;
  67   vp = v->_mp_d;
  68
  69   up += usize;                  /* point just above most significant limb */
  70   vp += vsize;                  /* point just above most significant limb */
  71
  72   count_leading_zeros (cnt, up[-1]);
  73   if ((vp[-1] >> (GMP_LIMB_BITS - 1 - cnt)) != 1)
  74     return 0;                   /* msb positions different */
  75
  76   n_bits += cnt - GMP_NAIL_BITS;
  77   n_limbs = (n_bits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS;
  78
  79   usize = MIN (usize, n_limbs);
  80   vsize = MIN (vsize, n_limbs);
  81
  82 #if 0
  83   /* Ignore zeros at the low end of U and V.  */
  84   while (up[0] == 0)
  85     up++, usize--;
  86   while (vp[0] == 0)
  87     vp++, vsize--;
  88 #endif
  89
  90   minsize = MIN (usize, vsize);
  91   maxsize = usize + vsize - minsize;
  92
  93   up -= minsize;                /* point at most significant common limb */
  94   vp -= minsize;                /* point at most significant common limb */
  95
  96   /* Compare the most significant part which has explicit limbs for U and V. */
  97   for (i = minsize - 1; i > 0; i--)
  98     {
  99       if (up[i] != vp[i])
 100         return 0;
 101     }
 102
 103   n_bits -= (maxsize - 1) * GMP_NUMB_BITS;
 104
 105   size = maxsize - minsize;
 106   if (size != 0)
 107     {
 108       if (up[0] != vp[0])
 109         return 0;
 110
 111       /* Now either U or V has its limbs consumed, i.e, continues with an
 112          infinite number of implicit zero limbs.  Check that the other operand
 113          has just zeros in the corresponding, relevant part.  */
 114
 115       if (usize > vsize)
 116         p = up - size;
 117       else
 118         p = vp - size;
 119
 120       for (i = size - 1; i > 0; i--)
 121         {
 122           if (p[i] != 0)
 123             return 0;
 124         }
 125
 126       diff = p[0];
 127     }
 128   else
 129     {
 130       /* Both U or V has its limbs consumed.  */
 131
 132       diff = up[0] ^ vp[0];
 133     }
 134
 135   if (n_bits < GMP_NUMB_BITS)
 136     diff >>= GMP_NUMB_BITS - n_bits;
 137
 138   return diff == 0;
 139 }