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#include "u.h"
#include "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "../port/error.h"
struct Rb
{
QLock;
Rendez producer;
Rendez consumer;
ulong randomcount;
uchar buf[1024];
uchar *ep;
uchar *rp;
uchar *wp;
uchar next;
uchar wakeme;
ushort bits;
ulong randn;
} rb;
static int
rbnotfull(void*)
{
int i;
i = rb.rp - rb.wp;
return i != 1 && i != (1 - sizeof(rb.buf));
}
static int
rbnotempty(void*)
{
return rb.wp != rb.rp;
}
static void
genrandom(void*)
{
up->basepri = PriNormal;
up->priority = up->basepri;
for(;;){
for(;;)
if(++rb.randomcount > 100000)
break;
if(anyhigher())
sched();
if(!rbnotfull(0))
sleep(&rb.producer, rbnotfull, 0);
}
}
/*
* produce random bits in a circular buffer
*/
static void
randomclock(void)
{
if(rb.randomcount == 0 || !rbnotfull(0))
return;
rb.bits = (rb.bits<<2) ^ rb.randomcount;
rb.randomcount = 0;
rb.next++;
if(rb.next != 8/2)
return;
rb.next = 0;
*rb.wp ^= rb.bits;
if(rb.wp+1 == rb.ep)
rb.wp = rb.buf;
else
rb.wp = rb.wp+1;
if(rb.wakeme)
wakeup(&rb.consumer);
}
void
randominit(void)
{
addclock0link(randomclock, 1000/HZ);
rb.ep = rb.buf + sizeof(rb.buf);
rb.rp = rb.wp = rb.buf;
kproc("genrandom", genrandom, 0);
}
/*
* consume random bytes from a circular buffer
*/
ulong
randomread(void *xp, ulong n)
{
uchar *e, *p;
ulong x;
p = xp;
if(waserror()){
qunlock(&rb);
nexterror();
}
qlock(&rb);
for(e = p + n; p < e; ){
if(rb.wp == rb.rp){
rb.wakeme = 1;
wakeup(&rb.producer);
sleep(&rb.consumer, rbnotempty, 0);
rb.wakeme = 0;
continue;
}
/*
* beating clocks will be precictable if
* they are synchronized. Use a cheap pseudo
* random number generator to obscure any cycles.
*/
x = rb.randn*1103515245 ^ *rb.rp;
*p++ = rb.randn = x;
if(rb.rp+1 == rb.ep)
rb.rp = rb.buf;
else
rb.rp = rb.rp+1;
}
qunlock(&rb);
poperror();
wakeup(&rb.producer);
return n;
}
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