// Emacs style mode select   -*- C++ -*-
//-----------------------------------------------------------------------------
//
// $Id: m_random.c,v 1.6 1998/05/03 23:13:18 killough Exp $
//
// Copyright (C) 1993-1996 by id Software, Inc.
//
// This source is available for distribution and/or modification
// only under the terms of the DOOM Source Code License as
// published by id Software. All rights reserved.
//
// The source is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// FITNESS FOR A PARTICULAR PURPOSE. See the DOOM Source Code License
// for more details.
//
//
// 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
//
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;

#if 0 // [RH]

  // 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;

#endif

  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;

  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
  // [RH] And it also seems to screws up netgame sync.

  //if (demo_insurance)
  //  boom += (gametic-level.starttime)*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
}

//----------------------------------------------------------------------------
//
// $Log: m_random.c,v $
// Revision 1.6  1998/05/03  23:13:18  killough
// Fix #include
//
// Revision 1.5  1998/03/31  10:43:05  killough
// Fix (supposed) RNG problems, add new demo_insurance
//
// Revision 1.4  1998/03/28  17:56:05  killough
// Improve RNG by adding external seed
//
// Revision 1.3  1998/02/17  05:40:08  killough
// Make RNGs local to each calling block, for demo sync
//
// Revision 1.2  1998/01/26  19:23:51  phares
// First rev with no ^Ms
//
// Revision 1.1.1.1  1998/01/19  14:02:58  rand
// Lee's Jan 19 sources
//
//----------------------------------------------------------------------------