src/gmxlib/lutab.c

   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  * Green Red Orange Magenta Azure Cyan Skyblue
  28  */
  29 static char *SRCID_lutab_c = "$Id$";
  30
  31 /*
  32  *      Invsqrt lookup tables @(#) gentab.c 1.9 11/5/92
  33  *
  34  *      Copyright (c) 1992, A. Sijbers, Groningen University
  35  */
  36 #include <math.h>
  37 #include "lutab.h"
  38 #include "callf77.h"
  39
  40 /* Global variable that is exported */
  41 t_lutab lookup_table;
  42
  43 static void init_table(t_lutab *lookup_table)
  44 {
  45   word index,addr;
  46   int new_exp,i,exp;
  47   t_convert bit_in,bit_out;
  48
  49   for (i=0; i<EXP_SEED_SIZE; i++)
  50     lookup_table->exp_seed[i]=NOT_INITIALISED;
  51   for (i=0; i<FRACT_SEED_SIZE; i++)
  52     lookup_table->fract_seed[i]=NOT_INITIALISED;
  53   for (i=0; i<EXP_SEED_SIZE; i++)
  54     {
  55       if ((exp=(i-127))<0) new_exp=127-((exp+1)/2); else new_exp=127-(exp/2)-1;
  56       lookup_table->exp_seed[i]=((new_exp)<<EXP_SHIFT)&EXP_MASK;
  57     }
  58   index=FRACT_FIRST;
  59   for (i=0; i<FRACT_SEED_SIZE; i++)
  60     {
  61       bit_in.bval=(index<<FRACT_SHIFT);
  62       addr=FRACT_ADDR(bit_in.bval);
  63       bit_out.fval=(1.0/sqrt(bit_in.fval));
  64       lookup_table->fract_seed[addr]=(bit_out.bval&FRACT_MASK);
  65       if (lookup_table->fract_seed[addr]==0)
  66         lookup_table->fract_seed[addr]=(MAX_FRACT&FRACT_MASK);
  67       index++;
  68     }
  69 }
  70
  71 void init_lookup_table(FILE *log)
  72 {
  73 #ifdef CINVSQRT
  74  if(log!=NULL)
  75      fprintf(log,"Generating lookup table for invsqrt calculation in C\n");
  76   init_table(&lookup_table);
  77 #endif
  78 #ifdef USEF77
  79 #ifdef FINVSQRT
  80   if(log!=NULL)
  81       fprintf(log,"Generating lookup table for invsqrt calculation in Fortran\n");
  82   fillbuf();
  83 #endif
  84 #endif
  85 }
  86