Diff: random.cpp

Revision:

0:f736749c33d2

Child:

2:0c241937eabd

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/random.cpp	Mon May 14 14:12:32 2018 +0000
@@ -0,0 +1,29 @@
+#include "random.h"
+#include "mbed.h"
+#include <limits.h>
+
+namespace random
+{       
+    AnalogIn noise(RANDOM_NOISE_PIN);
+    
+    void init() {
+        srand(noise.read_u16());
+    }
+    
+    uint16_t exponential(const uint16_t& tau_ms, const uint16_t& cutoff, const unsigned int& resolution){
+        double ftau     = (double)tau_ms;
+        double fcutoff  = (double)cutoff;
+        double cumulativeFraction = ((double)(rand() & resolution))/resolution;
+        
+        // calculate the point (in exponential distribution) from the inverse of its cumulative density function
+        double point = -ftau * log(1-cumulativeFraction);
+        
+        // return as uint16 value.
+        // if `point` is unreasonably long, then return `cutoff` instead.
+        if (point > fcutoff) {
+            return cutoff;
+        } else {
+            return (uint16_t)(point+0.5);
+        }
+    }
+}