include/lutab.h

   1 /*
   2  * $Id$
   3  *
   4  *       This source code is part of
   5  *
   6  *        G   R   O   M   A   C   S
   7  *
   8  * GROningen MAchine for Chemical Simulations
   9  *
  10  *               VERSION 2.0
  11  *
  12  * Copyright (c) 1991-1999
  13  * BIOSON Research Institute, Dept. of Biophysical Chemistry
  14  * University of Groningen, The Netherlands
  15  *
  16  * Please refer to:
  17  * GROMACS: A message-passing parallel molecular dynamics implementation
  18  * H.J.C. Berendsen, D. van der Spoel and R. van Drunen
  19  * Comp. Phys. Comm. 91, 43-56 (1995)
  20  *
  21  * Also check out our WWW page:
  22  * http://md.chem.rug.nl/~gmx
  23  * or e-mail to:
  24  * gromacs@chem.rug.nl
  25  *
  26  * And Hey:
  27  * Good ROcking Metal Altar for Chronical Sinners
  28  */
  29
  30 #ifndef _lutab_h
  31 #define _lutab_h
  32
  33 static char *SRCID_lutab_h = "$Id$";
  34
  35 #ifdef HAVE_IDENT
  36 #ident  "@(#) lutab.h 1.7 2/2/97"
  37 #endif /* HAVE_IDENT */
  38 /*
  39    Fast sqrt(x) routine (actually 1.0/sqrt(x)) By A. Sijbers (c) 1992
  40
  41    Based on Newton Rhapson iteration, initial value from lookup table
  42
  43    Floating point representation:
  44
  45          msb                                   lsb
  46          3322 2222 2222 1111 1111 1000 0000 0000
  47    bitnr 1098 7654 3210 9876 5432 1098 7654 3210
  48          |||| |||| |+-- ---- ---- ---- ---- ---+ fraction
  49          |+-- ---- + exponent
  50          +sign
  51
  52    S = sign
  53    E = exponent
  54    F = fraction
  55                       S  E-127
  56    IEEE : value = (-1) (2     ) (1.F)     <------ must be float representation
  57
  58                       S  E-128
  59    DEC  : value = (-1) (2     ) (0.1F)
  60 */
  61
  62 #include <stdio.h>
  63
  64 #define EXP_LSB         0x00800000
  65 #define EXP_SEED_SIZE   256
  66 #define EXP_MASK        0x7f800000
  67 #define EXP_SHIFT       23
  68 #define MAX_FRACT       0x007fffff
  69 #define FRACT_MASK      0x007fffff
  70 #define FRACT_SIZE      11              /* significant part of fraction */
  71 #define FRACT_SHIFT     (EXP_SHIFT-FRACT_SIZE)
  72 #define FRACT_SEED_SIZE (1<<(FRACT_SIZE+1))   /* one bit for even/odd */
  73 #define FRACT_FIRST     (0x3f800000>>FRACT_SHIFT)
  74 #define NOT_INITIALISED ~0
  75 #define EXP_ADDR(val)   (((val)&EXP_MASK)>>EXP_SHIFT)
  76 #define FRACT_ADDR(val) (((val)&(FRACT_MASK|EXP_LSB))>>FRACT_SHIFT)
  77
  78 typedef unsigned int word;
  79
  80 typedef union
  81 {
  82   word bval;
  83   float fval;
  84 } t_convert;
  85
  86 typedef struct
  87 {
  88   word exp_seed[EXP_SEED_SIZE];
  89   word fract_seed[FRACT_SEED_SIZE];
  90 } t_lutab;
  91
  92 /* Global variable, must be initiated by a call to init_lookup_table */
  93 extern t_lutab lookup_table;
  94
  95 extern void init_lookup_table(FILE *log);
  96
  97 #endif  /* _lutab_h */