/* rand.c - Don Yang (uguu.org)

   IBAA random number generator.  This is preferred over ISAAC because
   the source code to implement it is smaller.
   http://burtleburtle.net/bob/rand/isaac.html

   05/27/12
                                                                           */

#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<sys/time.h>

typedef unsigned int Word;
typedef unsigned char Byte;

/* Run one iteration of IBAA, returning random number in *result */
static void Ibaa(Word *memory, Word *accumulator, Word *index, Word *result)
{
   Word x, y;

   x = memory[*index];
   *accumulator = ((*accumulator) << 19) ^ ((*accumulator) >> 13);
   memory[*index] = y = memory[x & 0xff] + *accumulator + *result;
   *result = memory[(y >> 8) & 0xff] + x;
   *index = (*index + 1) & 0xff;
}

/* Append a string to memory block */
static void AddBlock(Byte *input, size_t size, Byte **output)
{
   for(; size > 0; size--)
   {
      **output = *input;
      ++*output;
      ++input;
   }
}

/* Initialize random state for Ibaa */
static void SeedIbaa(Word *memory, Word *accumulator, Word *index, Word *result)
{
   struct timeval timestamp;
   Word pid;
   Byte *output;
   int i;

   pid = (Word)getpid();
   gettimeofday(&timestamp, NULL);
   output = (Byte*)memory;
   AddBlock((Byte*)&pid, sizeof(pid), &output);
   AddBlock((Byte*)&timestamp, sizeof(timestamp), &output);
   AddBlock((Byte*)__TIME__, strlen(__TIME__), &output);
   AddBlock((Byte*)__DATE__, strlen(__DATE__), &output);
   for(i = 1; output < ((Byte*)memory) + 1024; i++)
      *output++ = (Byte)(i & 0xff);

   *index = *result = 0;
   *accumulator = 1;
   for(i = 0; i < 8192; i++)
      Ibaa(memory, accumulator, index, result);
}

/* Output a few random numbers to stdout */
int main(void)
{
   Word memory[256], accumulator, index, result;
   int i, j;

   SeedIbaa(memory, &accumulator, &index, &result);
   for(i = 0; i < 160; i += 8)
   {
      for(j = 0; j < 8; j++)
      {
         Ibaa(memory, &accumulator, &index, &result);
         printf("%08x ", result);
      }
      putchar('\n');
   }
   return 0;
}