Diff: core/random.cpp

Revision:

26:b4421d1ee57a

Parent:

13:8ea85a33e37a

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/core/random.cpp	Thu Jul 05 20:15:37 2018 +0000
@@ -0,0 +1,42 @@
+#include "random.h"
+#include "mbed.h"
+#include <limits.h>
+
+namespace random
+{       
+    AnalogIn noise(RANDOM_NOISE_PIN);
+    bool initialized = false;
+    
+    void init() {
+        srand(((uint32_t)noise.read_u16())<<16 & ((uint32_t)noise.read_u16()));
+        initialized = true;
+    }
+    
+    uint32_t unif(const uint32_t& nlevels) {
+        if (!initialized) {
+            init();
+        }
+        return ((uint32_t)rand()) % nlevels;
+    }
+    
+    uint32_t exponential(const uint32_t& tau, const uint32_t& cutoff, const unsigned int& resolution){
+        if (!initialized) {
+            init();
+        }
+        
+        double ftau     = (double)tau;
+        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 uint32 value.
+        // if `point` is unreasonably long, then return `cutoff` instead.
+        if (point > fcutoff) {
+            return cutoff;
+        } else {
+            return (uint32_t)(point+0.5);
+        }
+    }
+}