.:: Bots United ::. - Portable, self-contained replacements for RANDOM

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- - Portable, self-contained replacements for RANDOM_STUFF() (http://forums.bots-united.com/showthread.php?t=244)

Portable, self-contained replacements for RANDOM_STUFF()

since we can't use rand() for replacing RANDOM_LONG() and RANDOM_FLOAT() and thus save costy engine calls each time, because rand() only returns short integers and not longs, a portable, fast, and self-contained random number generator is something nice indeed

irwigo, w00t w00t mateys

Code:

// RACC - AI development project for first-person shooter games derived from Valve's Half-Life

// (http://racc.bots-united.com/)

//

// The game to engine interfacing code is based on the work done by Jeffrey 'botman' Broome

// (http://planethalflife.com/botman/)

//

// This project is partially based on the work done by Eric Bieschke in his BSDbot

// (http://gamershomepage.com/csbot/)

//

// This project is partially based on the work done by Brendan "Spyro" McCarthy in his ODD Bot

// (http://oddbot.hlfusion.com/)

//

// This project is partially based on the work done by Alistair 'eLiTe' Stewart in his TEAMbot

// (http://www.planethalflife.com/teambot/)

//

// Rational Autonomous Cybernetic Commandos AI

//

// lrand.cpp

//

 

#include "racc.h"

 

 

// maximum value returned by our number generator (2^31 - 1 = 0x7FFFFFFF)

#define LRAND_MAX 2147483647L

 

 

long lseed; // our random number generator's seed

 

 

void lsrand (unsigned long initial_seed)

{

   // this function initializes the random seed based on the initial seed value passed in the

   // initial_seed parameter. Since random seeds are usually initialized with the time of day,

   // and time is a value that changes slowly, we bump the seed twice to have it in a more

   // random state for future calls of the random number generator.

 

   lseed = (long) initial_seed; // fill in the initial seed of the random number generator

   lseed = lrand (); // bump it once

   lseed = lrand (); // bump it twice

 

   return; // that's all folks

}

 

 

long lrand (void)

{

   // this function is the equivalent of the rand() standard C library function, except that

   // whereas rand() works only with short integers (i.e. not above 32767), this function is

   // able to generate 32-bit random numbers. Isn't that nice ?

 

   // credits go to Ray Gardner for his fast implementation of minimal random number generators

   // http://c.snippets.org/snip_lister.php?fname=rg_rand.c

 

   static unsigned long lrand_lo, lrand_hi;

 

   // compose the two 16-bit parts of the long integer and assemble them

   lrand_lo = 16807 * (long) (lseed & 0xFFFF); // low part

   lrand_hi = 16807 * (long) ((unsigned long) lseed >> 16); // high part

   lrand_lo += (lrand_hi & 0x7FFF) << 16; // assemble both in lrand_lo

 

   // is the resulting number greater than LRAND_MAX (half the capacity) ?

   if (lrand_lo > LRAND_MAX)

   {

          lrand_lo &= LRAND_MAX; // then get rid of the disturbing bit

          lrand_lo++; // and increase it a bit (to avoid overflow problems, I suppose)

   }

 

   lrand_lo += lrand_hi >> 15; // now do twisted maths to generate the next seed

 

   // is the resulting number greater than LRAND_MAX (half the capacity) ?

   if (lrand_lo > LRAND_MAX)

   {

          lrand_lo &= LRAND_MAX; // then get rid of the disturbing bit

          lrand_lo++; // and increase it a bit (to avoid overflow problems, I suppose)

   }

 

   // now we've got our (pseudo-)random number.

 

   lseed = (long) lrand_lo; // put it in the seed for next time

   return (lseed); // and return it. Yeah, simple as that.

}

 

 

long RandomLong (long from, long to)

{

   // this function returns a random integer number between (and including) the starting and

   // ending values passed by parameters from and to.

 

   if (to <= from)

          return (from);

 

   return (from + lrand () / (LRAND_MAX / (to - from + 1)));

}

 

 

float RandomFloat (float from, float to)

{

   // this function returns a random floating-point number between (and including) the starting

   // and ending values passed by parameters from and to.

 

   if (to <= from)

          return (from);

 

   return (from + (float) lrand () / (LRAND_MAX / (to - from)));

}

 

 

// "Anyone who consider arithmetic means of producing random number is,

// of course, in a state of sin"

//                                 -- John Von Neumann