rockbox/apps/plugins/doom/m_random.c

/* Emacs style mode select   -*- C++ -*-
 *-----------------------------------------------------------------------------
 *
 *
 *  PrBoom a Doom port merged with LxDoom and LSDLDoom
 *  based on BOOM, a modified and improved DOOM engine
 *  Copyright (C) 1999 by
 *  id Software, Chi Hoang, Lee Killough, Jim Flynn, Rand Phares, Ty Halderman
 *  Copyright (C) 1999-2000 by
 *  Jess Haas, Nicolas Kalkhof, Colin Phipps, Florian Schulze
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version 2
 *  of the License, or (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 *  02111-1307, USA.
 *
 * DESCRIPTION:
 *      Random number LUT.
 *
 * 1/19/98 killough: Rewrote random number generator for better randomness,
 * while at the same time maintaining demo sync and backward compatibility.
 *
 * 2/16/98 killough: Made each RNG local to each control-equivalent block,
 * to reduce the chances of demo sync problems.
 *
 *-----------------------------------------------------------------------------*/


#include "doomstat.h"
#include "m_random.h"

//
// M_Random
// Returns a 0-255 number
//
static const unsigned char rndtable[256] = { // 1/19/98 killough -- made const
         0,   8, 109, 220, 222, 241, 149, 107,  75, 248, 254, 140,  16,  66 ,
         74,  21, 211,  47,  80, 242, 154,  27, 205, 128, 161,  89,  77,  36 ,
         95, 110,  85,  48, 212, 140, 211, 249,  22,  79, 200,  50,  28, 188 ,
         52, 140, 202, 120,  68, 145,  62,  70, 184, 190,  91, 197, 152, 224 ,
         149, 104,  25, 178, 252, 182, 202, 182, 141, 197,   4,  81, 181, 242 ,
         145,  42,  39, 227, 156, 198, 225, 193, 219,  93, 122, 175, 249,   0 ,
         175, 143,  70, 239,  46, 246, 163,  53, 163, 109, 168, 135,   2, 235 ,
         25,  92,  20, 145, 138,  77,  69, 166,  78, 176, 173, 212, 166, 113 ,
         94, 161,  41,  50, 239,  49, 111, 164,  70,  60,   2,  37, 171,  75 ,
         136, 156,  11,  56,  42, 146, 138, 229,  73, 146,  77,  61,  98, 196 ,
         135, 106,  63, 197, 195,  86,  96, 203, 113, 101, 170, 247, 181, 113 ,
         80, 250, 108,   7, 255, 237, 129, 226,  79, 107, 112, 166, 103, 241 ,
         24, 223, 239, 120, 198,  58,  60,  82, 128,   3, 184,  66, 143, 224 ,
         145, 224,  81, 206, 163,  45,  63,  90, 168, 114,  59,  33, 159,  95 ,
         28, 139, 123,  98, 125, 196,  15,  70, 194, 253,  54,  14, 109, 226 ,
         71,  17, 161,  93, 186,  87, 244, 138,  20,  52, 123, 251,  26,  36 ,
         17,  46,  52, 231, 232,  76,  31, 221,  84,  37, 216, 165, 212, 106 ,
         197, 242,  98,  43,  39, 175, 254, 145, 190,  84, 118, 222, 187, 136 ,
         120, 163, 236, 249
      };

rng_t rng;     // the random number state

unsigned long rngseed = 1993;   // killough 3/26/98: The seed

int P_Random(pr_class_t pr_class)
{
   // killough 2/16/98:  We always update both sets of random number
   // generators, to ensure repeatability if the demo_compatibility
   // flag is changed while the program is running. Changing the
   // demo_compatibility flag does not change the sequences generated,
   // only which one is selected from.
   //
   // All of this RNG stuff is tricky as far as demo sync goes --
   // it's like playing with explosives :) Lee

   int compat = pr_class == pr_misc ?
                (rng.prndindex = (rng.prndindex + 1) & 255) :
                (rng. rndindex = (rng. rndindex + 1) & 255) ;

   unsigned long boom;

   // killough 3/31/98:
   // If demo sync insurance is not requested, use
   // much more unstable method by putting everything
   // except pr_misc into pr_all_in_one

   if (pr_class != pr_misc && !demo_insurance)      // killough 3/31/98
      pr_class = pr_all_in_one;

   boom = rng.seed[pr_class];

   // killough 3/26/98: add pr_class*2 to addend

   rng.seed[pr_class] = boom * 1664525ul + 221297ul + pr_class*2;

   if (demo_compatibility)
      return rndtable[compat];

   boom >>= 20;

   /* killough 3/30/98: use gametic-levelstarttic to shuffle RNG
    * killough 3/31/98: but only if demo insurance requested,
    * since it's unnecessary for random shuffling otherwise
    * killough 9/29/98: but use basetic now instead of levelstarttic
    * cph - DEMOSYNC - this change makes MBF demos work,
    *       but does it break Boom ones?
    */

   if (demo_insurance)
      boom += (gametic-basetic)*7;

   return boom & 255;
}

// Initialize all the seeds
//
// This initialization method is critical to maintaining demo sync.
// Each seed is initialized according to its class, so if new classes
// are added they must be added to end of pr_class_t list. killough
//

void M_ClearRandom (void)
{
   int i;
   unsigned long seed = rngseed*2+1;    // add 3/26/98: add rngseed
   for (i=0; i<NUMPRCLASS; i++)         // go through each pr_class and set
      rng.seed[i] = seed *= 69069ul;     // each starting seed differently
   rng.prndindex = rng.rndindex = 0;    // clear two compatibility indices
}