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

   Original:
   http://burtleburtle.net/bob/rand/isaacafa.html
   
   07/29/12
                                                                           */
#include<stdio.h>
#include<string.h>

typedef unsigned int ub4;

static ub4 result[256], result_count = 0;
static ub4 mm[256], aa = 0, bb = 0, cc = 0;

static ub4 Isaac(void)
{
   ub4 i, x, y;

   if( result_count-- == 0 )
   {
      cc++;
      bb += cc;
      
      for(i = 0; i < 256; i++)
      {
         x = mm[i];
         #if 0
            switch( i & 3 )
            {
               case 0: aa ^= (aa << 13); break;
               case 1: aa ^= (aa >> 6); break;
               case 2: aa ^= (aa << 2); break;
               case 3: aa ^= (aa >> 16); break;
            }
         #else
            aa ^= (i & 1) ? aa >> ((i & 2) ? 16 : 6)
                          : aa << ((i & 2) ? 2 : 13);
         #endif
         aa += mm[(i + 128) & 255];
         mm[i] = y = mm[(x >> 2) & 255] + aa + bb;
         result[i] = bb = mm[(y >> 10) & 255] + x;
      }

      result_count = 255;
   }
   return result[result_count];
}

int main(void)
{
   int i;

   memset(mm, 0, sizeof(mm));

   for(i = 0; i < 256 * 10; i++)
      Isaac();
   printf("aa=%08x bb=%08x cc=%08x\n", aa, bb, cc);
   for(i = 0; i < (1 << 27); i++)
      Isaac();
   for(i = 0; i < 256; i++)
      printf("%08x\n", Isaac());

   return 0;
}