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2 - 1 
#include	"u.h"
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#include	"../port/lib.h"
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#include	"mem.h"
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#include	"dat.h"
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#include	"fns.h"
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#include	"../port/error.h"
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struct Rb
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{
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	QLock;
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	Rendez	producer;
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	Rendez	consumer;
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	ulong	randomcount;
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	uchar	buf[1024];
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	uchar	*ep;
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	uchar	*rp;
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	uchar	*wp;
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	uchar	next;
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	uchar	wakeme;
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	ushort	bits;
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	ulong	randn;
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} rb;
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static int
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rbnotfull(void*)
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{
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	int i;
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	i = rb.rp - rb.wp;
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	return i != 1 && i != (1 - sizeof(rb.buf));
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}
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static int
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rbnotempty(void*)
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{
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	return rb.wp != rb.rp;
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}
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static void
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genrandom(void*)
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{
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	up->basepri = PriNormal;
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	up->priority = up->basepri;
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	for(;;){
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		for(;;)
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			if(++rb.randomcount > 100000)
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				break;
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		if(anyhigher())
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			sched();
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		if(!rbnotfull(0))
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			sleep(&rb.producer, rbnotfull, 0);
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	}
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}
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/*
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 *  produce random bits in a circular buffer
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 */
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static void
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randomclock(void)
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{
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	if(rb.randomcount == 0 || !rbnotfull(0))
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		return;
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	rb.bits = (rb.bits<<2) ^ rb.randomcount;
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	rb.randomcount = 0;
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	rb.next++;
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	if(rb.next != 8/2)
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		return;
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	rb.next = 0;
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	*rb.wp ^= rb.bits;
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	if(rb.wp+1 == rb.ep)
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		rb.wp = rb.buf;
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	else
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		rb.wp = rb.wp+1;
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	if(rb.wakeme)
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		wakeup(&rb.consumer);
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}
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void
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randominit(void)
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{
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	/* Frequency close but not equal to HZ */
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	addclock0link(randomclock, 13);
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	rb.ep = rb.buf + sizeof(rb.buf);
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	rb.rp = rb.wp = rb.buf;
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	kproc("genrandom", genrandom, 0);
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}
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/*
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 *  consume random bytes from a circular buffer
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 */
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ulong
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randomread(void *xp, ulong n)
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{
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	uchar *e, *p;
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	ulong x;
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	p = xp;
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	if(waserror()){
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		qunlock(&rb);
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		nexterror();
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	}
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	qlock(&rb);
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	for(e = p + n; p < e; ){
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		if(rb.wp == rb.rp){
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			rb.wakeme = 1;
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			wakeup(&rb.producer);
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			sleep(&rb.consumer, rbnotempty, 0);
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			rb.wakeme = 0;
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			continue;
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		}
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		/*
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		 *  beating clocks will be predictable if
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		 *  they are synchronized.  Use a cheap pseudo-
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		 *  random number generator to obscure any cycles.
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		 */
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		x = rb.randn*1103515245 ^ *rb.rp;
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		*p++ = rb.randn = x;
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		if(rb.rp+1 == rb.ep)
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			rb.rp = rb.buf;
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		else
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			rb.rp = rb.rp+1;
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	}
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	qunlock(&rb);
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	poperror();
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	wakeup(&rb.producer);
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	return n;
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}