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/*
------------------------------------------------------------------------------
isaac.c: By Bob Jenkins. My random number generator, ISAAC.
MODIFIED:
960327: Creation (addition of randinit, really)
970719: use context, not global variables, for internal state
980324: make a portable version
991209: modified for inclusion with GNU Backgammon by Gary Wong
070121: modified for inclusion with flam3 by Erik Reckase
------------------------------------------------------------------------------
*/
#include "isaacs.h"
#include "isaac.h"
#define ind(mm,x) ((mm)[(x>>2)&(RANDSIZ-1)])
#define rngstep(mix,a,b,mm,m,m2,r,x) \
{ \
x = *m; \
a = ((a^(mix)) + *(m2++)) & 0xffffffff; \
*(m++) = y = (ind(mm,x) + a + b) & 0xffffffff; \
*(r++) = b = (ind(mm,y>>RANDSIZL) + x) & 0xffffffff; \
}
void isaac(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)) & 0xffffffff;
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 irandinit(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
{
for (i=0; i<RANDSIZ; i+=8)
{
/* fill in mm[] with messy stuff */
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 */
}
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