1 files changed, 156 insertions, 0 deletions
diff --git a/os/port/random.c b/os/port/random.c
new file mode 100644
index 00000000..720541c0
--- /dev/null
+++ b/os/port/random.c
@@ -0,0 +1,156 @@
+#include	"u.h"
+#include	"../port/lib.h"
+#include	"mem.h"
+#include	"dat.h"
+#include	"fns.h"
+
+static struct
+{
+	QLock;
+	Rendez	producer;
+	Rendez	consumer;
+	ulong	randomcount;
+	uchar	buf[1024];
+	uchar	*ep;
+	uchar	*rp;
+	uchar	*wp;
+	uchar	next;
+	uchar	bits;
+	uchar	wakeme;
+	uchar	filled;
+	int	target;
+	int	kprocstarted;
+	ulong	randn;
+} rb;
+
+static int
+rbnotfull(void*)
+{
+	int i;
+
+	i = rb.wp - rb.rp;
+	if(i < 0)
+		i += sizeof(rb.buf);
+	return i < rb.target;
+}
+
+static int
+rbnotempty(void*)
+{
+	return rb.wp != rb.rp;
+}
+
+static void
+genrandom(void*)
+{
+	setpri(PriBackground);
+
+	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)
+{
+	uchar *p;
+
+	if(rb.randomcount == 0)
+		return;
+
+	if(!rbnotfull(0)) {
+		rb.filled = 1;
+		return;
+	}
+
+	rb.bits = (rb.bits<<2) ^ (rb.randomcount&3);
+	rb.randomcount = 0;
+
+	rb.next += 2;
+	if(rb.next != 8)
+		return;
+
+	rb.next = 0;
+	*rb.wp ^= rb.bits ^ *rb.rp;
+	p = rb.wp+1;
+	if(p == rb.ep)
+		p = rb.buf;
+	rb.wp = p;
+
+	if(rb.wakeme)
+		wakeup(&rb.consumer);
+}
+
+void
+randominit(void)
+{
+	/* Frequency close but not equal to HZ */
+	addclock0link(randomclock, 13);
+	rb.target = 16;
+	rb.ep = rb.buf + sizeof(rb.buf);
+	rb.rp = rb.wp = rb.buf;
+}
+
+/*
+ *  consume random bytes from a circular buffer
+ */
+ulong
+randomread(void *xp, ulong n)
+{
+	int i, sofar;
+	uchar *e, *p;
+
+	p = xp;
+
+	qlock(&rb);
+	if(waserror()){
+		qunlock(&rb);
+		nexterror();
+	}
+	if(!rb.kprocstarted){
+		rb.kprocstarted = 1;
+		kproc("genrand", genrandom, nil, 0);
+	}
+
+	for(sofar = 0; sofar < n; sofar += i){
+		i = rb.wp - rb.rp;
+		if(i == 0){
+			rb.wakeme = 1;
+			wakeup(&rb.producer);
+			sleep(&rb.consumer, rbnotempty, 0);
+			rb.wakeme = 0;
+			continue;
+		}
+		if(i < 0)
+			i = rb.ep - rb.rp;
+		if((i+sofar) > n)
+			i = n - sofar;
+		memmove(p + sofar, rb.rp, i);
+		e = rb.rp + i;
+		if(e == rb.ep)
+			e = rb.buf;
+		rb.rp = e;
+	}
+	if(rb.filled && rb.wp == rb.rp){
+		i = 2*rb.target;
+		if(i > sizeof(rb.buf) - 1)
+			i = sizeof(rb.buf) - 1;
+		rb.target = i;
+		rb.filled = 0;
+	}
+	poperror();
+	qunlock(&rb);
+
+	wakeup(&rb.producer);
+
+	return n;
+}