```/*
------------------------------------------------------------------------------
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 "standard.h"
#endif
#ifndef RAND
#include "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
```