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