From c0a7b53baf2a6e7bf9bc1fbec7ac05e43ac59154 Mon Sep 17 00:00:00 2001
From: Nicholas Noll <nbnoll@eml.cc>
Date: Wed, 8 Sep 2021 15:51:40 -0700
Subject: checkin

---
 sys/libn/random.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

(limited to 'sys/libn/random.c')

diff --git a/sys/libn/random.c b/sys/libn/random.c
index 558641e..551d1e9 100644
--- a/sys/libn/random.c
+++ b/sys/libn/random.c
@@ -1,4 +1,5 @@
 #include <u.h>
+#include <libn.h>
 
 // ----------------------------------------------------------------------------
 // Internal structure
@@ -66,12 +67,29 @@ rng·init(uint64 seed)
 
 /* Returns a random float64 between 0 and 1 */
 double
-rng·random()
+rng·random(void)
 {
     uint64 r = xoshiro256ss(&RNG); 
     return (double)r / (double)UINT64_MAX;
 }
 
+double
+rng·exponential(double lambda)
+{
+    double f;
+
+    f = rng·random();
+    return -log(1 - f)/lambda;
+}
+
+double
+rng·normal(void)
+{
+    double f;
+    f = rng·random();
+
+}
+
 /* Returns true or false on success of trial */
 bool
 rng·bernoulli(double f)
@@ -88,3 +106,18 @@ rng·randi(int max)
     uint64 r = xoshiro256ss(&RNG); 
     return r % max;
 }
+
+uint64
+rng·poisson(double mean)
+{
+    uint64 n;
+    double c;
+
+    if(mean<10.0) {
+        for(n=0, c=rng·exponential(1.0); c<mean; ++n, c+=rng·exponential(1.0))
+            ;
+        return n;
+    }
+
+    return 0;
+}
-- 
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