contrib/gmp/mpf/reldiff.c

   1 /* mpf_reldiff -- Generate the relative difference of two floats.
   2
   3 Copyright 1996, 2001, 2004, 2005 Free Software Foundation, Inc.
   4
   5 This file is part of the GNU MP Library.
   6
   7 The GNU MP Library is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU Lesser General Public License as published by
   9 the Free Software Foundation; either version 3 of the License, or (at your
  10 option) any later version.
  11
  12 The GNU MP Library is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15 License for more details.
  16
  17 You should have received a copy of the GNU Lesser General Public License
  18 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  19
  20 #include "gmp.h"
  21 #include "gmp-impl.h"
  22
  23
  24 /* The precision we use for d = x-y is based on what mpf_div will want from
  25    the dividend.  It calls mpn_tdiv_qr to produce a quotient of rprec+1
  26    limbs.  So rprec+1 == dsize - xsize + 1, hence dprec = rprec+xsize.  */
  27
  28 void
  29 mpf_reldiff (mpf_t rdiff, mpf_srcptr x, mpf_srcptr y)
  30 {
  31   if (UNLIKELY (SIZ(x) == 0))
  32     {
  33       mpf_set_ui (rdiff, (unsigned long int) (mpf_sgn (y) != 0));
  34     }
  35   else
  36     {
  37       mp_size_t dprec;
  38       mpf_t d;
  39       TMP_DECL;
  40
  41       TMP_MARK;
  42       dprec = PREC(rdiff) + ABSIZ(x);
  43       ASSERT (PREC(rdiff)+1 == dprec - ABSIZ(x) + 1);
  44
  45       PREC(d) = dprec;
  46       PTR(d) = TMP_ALLOC_LIMBS (dprec + 1);
  47
  48       mpf_sub (d, x, y);
  49       SIZ(d) = ABSIZ(d);
  50       mpf_div (rdiff, d, x);
  51
  52       TMP_FREE;
  53     }
  54 }