contrib/gdtoa/ulp.c

   1 /****************************************************************
   2
   3 The author of this software is David M. Gay.
   4
   5 Copyright (C) 1998, 1999 by Lucent Technologies
   6 All Rights Reserved
   7
   8 Permission to use, copy, modify, and distribute this software and
   9 its documentation for any purpose and without fee is hereby
  10 granted, provided that the above copyright notice appear in all
  11 copies and that both that the copyright notice and this
  12 permission notice and warranty disclaimer appear in supporting
  13 documentation, and that the name of Lucent or any of its entities
  14 not be used in advertising or publicity pertaining to
  15 distribution of the software without specific, written prior
  16 permission.
  17
  18 LUCENT DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
  19 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.
  20 IN NO EVENT SHALL LUCENT OR ANY OF ITS ENTITIES BE LIABLE FOR ANY
  21 SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  22 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER
  23 IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
  24 ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
  25 THIS SOFTWARE.
  26
  27 ****************************************************************/
  28
  29 /* Please send bug reports to David M. Gay (dmg at acm dot org,
  30  * with " at " changed at "@" and " dot " changed to ".").      */
  31
  32 #include "gdtoaimp.h"
  33
  34  double
  35 ulp
  36 #ifdef KR_headers
  37         (x) U *x;
  38 #else
  39         (U *x)
  40 #endif
  41 {
  42         Long L;
  43         U a;
  44
  45         L = (word0(x) & Exp_mask) - (P-1)*Exp_msk1;
  46 #ifndef Sudden_Underflow
  47         if (L > 0) {
  48 #endif
  49 #ifdef IBM
  50                 L |= Exp_msk1 >> 4;
  51 #endif
  52                 word0(&a) = L;
  53                 word1(&a) = 0;
  54 #ifndef Sudden_Underflow
  55                 }
  56         else {
  57                 L = -L >> Exp_shift;
  58                 if (L < Exp_shift) {
  59                         word0(&a) = 0x80000 >> L;
  60                         word1(&a) = 0;
  61                         }
  62                 else {
  63                         word0(&a) = 0;
  64                         L -= Exp_shift;
  65                         word1(&a) = L >= 31 ? 1 : 1 << (31 - L);
  66                         }
  67                 }
  68 #endif
  69         return dval(&a);
  70         }