planarity/random.c

   1 /*
   2  *
   3  *  gPlanarity:
   4  *     The geeky little puzzle game with a big noodly crunch!
   5  *
   6  *     gPlanarity copyright (C) 2005 Monty <monty@xiph.org>
   7  *     Original Flash game by John Tantalo <john.tantalo@case.edu>
   8  *     Original game concept by Mary Radcliffe
   9  *
  10  *  gPlanarity is free software; you can redistribute it and/or modify
  11  *  it under the terms of the GNU General Public License as published by
  12  *  the Free Software Foundation; either version 2, or (at your option)
  13  *  any later version.
  14  *
  15  *  gPlanarity is distributed in the hope that it will be useful,
  16  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  *  GNU General Public License for more details.
  19  *
  20  *  You should have received a copy of the GNU General Public License
  21  *  along with Postfish; see the file COPYING.  If not, write to the
  22  *  Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  23  *
  24  *
  25  */
  26
  27 #include "random.h"
  28
  29 // Portable 32 bit random number generator.  It's not crypto-grade,
  30 // but we don't need crypto-grade.  We need complete control over the
  31 // result sequence and reproducability, so we can't use any local
  32 // generator.  As long as it's 100% consistent across
  33 // platforms/OSes/compilers and fairly uniform (doesn't always return
  34 // 17), we're all set.
  35
  36 // This is a C derivative of the PASCAL "Integer Version 2" minimal
  37 // standard number generator thich appears in the article:
  38 //     Park, Steven K. and Miller, Keith W., "Random Number
  39 //     Generators: Good Ones are Hard to Find", Communications of the
  40 //     ACM, October, 1988.
  41
  42
  43 static int32_t next = 123456789;
  44
  45 void random_seed(int32_t seed){
  46   next = seed;
  47 }
  48
  49 #define MPLIER     16807
  50 #define MOBYMP     127773
  51 #define MOMDMP     2836
  52
  53 int32_t random_number(){
  54   int32_t hival, loval, testval;
  55
  56   hival = next / MOBYMP;
  57   loval = next % MOBYMP;
  58   testval = MPLIER*loval - MOMDMP*hival;
  59   if (testval > 0)
  60     next = testval;
  61   else
  62     next = testval + MAX_G_RAND;
  63
  64   return next;
  65 }
  66
  67 int random_yes(int per128_yes){
  68   u_int32_t num = (u_int32_t)random_number();
  69   return (num < (unsigned int)per128_yes << 24U);
  70 }