File: isaac_rand.c

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/*
------------------------------------------------------------------------------
rand.c: By Bob Jenkins.  My random number generator, ISAAC.  Public Domain.
MODIFIED:
  960327: Creation (addition of randinit, really)
  970719: use context, not global variables, for internal state
  980324: added main (ifdef'ed out), also rearranged randinit()
  010626: Note that this is public domain
------------------------------------------------------------------------------
*/
#ifndef STANDARD
#include "isaac_standard.h"
#endif
#ifndef RAND
#include "isaac_rand.h"
#endif


#define ind(mm,x)  (*(ub4 *)((ub1 *)(mm) + ((x) & ((RANDSIZ-1)<<2))))
#define rngstep(mix,a,b,mm,m,m2,r,x) \
{ \
  x = *m;  \
  a = (a^(mix)) + *(m2++); \
  *(m++) = y = ind(mm,x) + a + b; \
  *(r++) = b = ind(mm,y>>RANDSIZL) + x; \
}

void     isaac(ctx)
randctx *ctx;
{
   register ub4 a,b,x,y,*m,*mm,*m2,*r,*mend;
   mm=ctx->randmem; 
   r=ctx->randrsl;
   a = ctx->randa; 
   b = ctx->randb + (++ctx->randc);
   for (m = mm, mend = m2 = m+(RANDSIZ/2); m<mend; )
   {
      rngstep( a<<13, a, b, mm, m, m2, r, x);
      rngstep( a>>6 , a, b, mm, m, m2, r, x);
      rngstep( a<<2 , a, b, mm, m, m2, r, x);
      rngstep( a>>16, a, b, mm, m, m2, r, x);
   }
   for (m2 = mm; m2<mend; )
   {
      rngstep( a<<13, a, b, mm, m, m2, r, x);
      rngstep( a>>6 , a, b, mm, m, m2, r, x);
      rngstep( a<<2 , a, b, mm, m, m2, r, x);
      rngstep( a>>16, a, b, mm, m, m2, r, x);
   }
   ctx->randb = b; ctx->randa = a;
}


#define mix(a,b,c,d,e,f,g,h) \
{ \
   a^=b<<11; d+=a; b+=c; \
   b^=c>>2;  e+=b; c+=d; \
   c^=d<<8;  f+=c; d+=e; \
   d^=e>>16; g+=d; e+=f; \
   e^=f<<10; h+=e; f+=g; \
   f^=g>>4;  a+=f; g+=h; \
   g^=h<<8;  b+=g; h+=a; \
   h^=a>>9;  c+=h; a+=b; \
}

/* if (flag==TRUE), then use the contents of randrsl[] to initialize mm[]. */
void randinit(ctx, flag)
randctx *ctx;
word     flag;
{
   word i;
   ub4 a,b,c,d,e,f,g,h;
   ub4 *m,*r;
   ctx->randa = ctx->randb = ctx->randc = 0;
   m=ctx->randmem;
   r=ctx->randrsl;
   a=b=c=d=e=f=g=h=0x9e3779b9;  /* the golden ratio */

   for (i=0; i<4; ++i)          /* scramble it */
   {
     mix(a,b,c,d,e,f,g,h);
   }

   if (flag) 
   {
     /* initialize using the contents of r[] as the seed */
     for (i=0; i<RANDSIZ; i+=8)
     {
       a+=r[i  ]; 
       b+=r[i+1];
       c+=r[i+2]; 
       d+=r[i+3];
       e+=r[i+4]; 
       f+=r[i+5]; 
       g+=r[i+6]; 
       h+=r[i+7];
       mix(a,b,c,d,e,f,g,h);
       m[i  ]=a; 
       m[i+1]=b; 
       m[i+2]=c; 
       m[i+3]=d;
       m[i+4]=e; 
       m[i+5]=f; 
       m[i+6]=g; 
       m[i+7]=h;
     }
     /* do a second pass to make all of the seed affect all of m */
     for (i=0; i<RANDSIZ; i+=8)
     {
       a+=m[i  ]; 
       b+=m[i+1]; 
       c+=m[i+2]; 
       d+=m[i+3];
       e+=m[i+4]; 
       f+=m[i+5]; 
       g+=m[i+6]; 
       h+=m[i+7];
       mix(a,b,c,d,e,f,g,h);
       m[i  ]=a; 
       m[i+1]=b; 
       m[i+2]=c; 
       m[i+3]=d;
       m[i+4]=e; 
       m[i+5]=f; 
       m[i+6]=g; 
       m[i+7]=h;
     }
   }
   else
   {
     /* fill in m[] with messy stuff */
     for (i=0; i<RANDSIZ; i+=8)
     {
       mix(a,b,c,d,e,f,g,h);
       m[i  ]=a; 
       m[i+1]=b; 
       m[i+2]=c; 
       m[i+3]=d;
       m[i+4]=e; 
       m[i+5]=f; 
       m[i+6]=g; 
       m[i+7]=h;
     }
   }

   isaac(ctx);            /* fill in the first set of results */
   ctx->randcnt=RANDSIZ;  /* prepare to use the first set of results */
}


#ifdef NEVER
int main()
{
  ub4 i,j;
  randctx ctx;
  ctx.randa=ctx.randb=ctx.randc=(ub4)0;
  for (i=0; i<256; ++i) ctx.randrsl[i]=(ub4)0;
  randinit(&ctx, TRUE);
  for (i=0; i<2; ++i)
  {
    isaac(&ctx);
    for (j=0; j<256; ++j)
    {
      printf("%.8lx",ctx.randrsl[j]);
      if ((j&7)==7) printf("\n");
    }
  }
}
#endif