arch/mips/math-emu/dp_modf.c

   1 /* IEEE754 floating point arithmetic
   2  * double precision: common utilities
   3  */
   4 /*
   5  * MIPS floating point support
   6  * Copyright (C) 1994-2000 Algorithmics Ltd.
   7  * http://www.algor.co.uk
   8  *
   9  * ########################################################################
  10  *
  11  *  This program is free software; you can distribute it and/or modify it
  12  *  under the terms of the GNU General Public License (Version 2) as
  13  *  published by the Free Software Foundation.
  14  *
  15  *  This program is distributed in the hope it will be useful, but WITHOUT
  16  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  17  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  18  *  for more details.
  19  *
  20  *  You should have received a copy of the GNU General Public License along
  21  *  with this program; if not, write to the Free Software Foundation, Inc.,
  22  *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
  23  *
  24  * ########################################################################
  25  */
  26
  27
  28 #include "ieee754dp.h"
  29
  30 /* modf function is always exact for a finite number
  31 */
  32 ieee754dp ieee754dp_modf(ieee754dp x, ieee754dp * ip)
  33 {
  34         COMPXDP;
  35
  36         CLEARCX;
  37
  38         EXPLODEXDP;
  39
  40         switch (xc) {
  41         case IEEE754_CLASS_SNAN:
  42         case IEEE754_CLASS_QNAN:
  43         case IEEE754_CLASS_INF:
  44         case IEEE754_CLASS_ZERO:
  45                 *ip = x;
  46                 return x;
  47         case IEEE754_CLASS_DNORM:
  48                 /* far to small */
  49                 *ip = ieee754dp_zero(xs);
  50                 return x;
  51         case IEEE754_CLASS_NORM:
  52                 break;
  53         }
  54         if (xe < 0) {
  55                 *ip = ieee754dp_zero(xs);
  56                 return x;
  57         }
  58         if (xe >= DP_MBITS) {
  59                 *ip = x;
  60                 return ieee754dp_zero(xs);
  61         }
  62         /* generate ipart mantissa by clearing bottom bits
  63          */
  64         *ip = builddp(xs, xe + DP_EBIAS,
  65                       ((xm >> (DP_MBITS - xe)) << (DP_MBITS - xe)) &
  66                       ~DP_HIDDEN_BIT);
  67
  68         /* generate fpart mantissa by clearing top bits
  69          * and normalizing (must be able to normalize)
  70          */
  71         xm = (xm << (64 - (DP_MBITS - xe))) >> (64 - (DP_MBITS - xe));
  72         if (xm == 0)
  73                 return ieee754dp_zero(xs);
  74
  75         while ((xm >> DP_MBITS) == 0) {
  76                 xm <<= 1;
  77                 xe--;
  78         }
  79         return builddp(xs, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
  80 }