From 2bb32bd4b0699f70674b1a9537155814463cae0f Mon Sep 17 00:00:00 2001
From: lbernstone <lbernstone@gmail.com>
Date: Mon, 18 Feb 2019 03:18:49 -0700
Subject: [PATCH] Unbiased random (#2468)

* An example to read high frequency analog data using i2s_adc

* Changed random() to use Lemire's method for bounding
---
 cores/esp32/WMath.cpp | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/cores/esp32/WMath.cpp b/cores/esp32/WMath.cpp
index b1099b67..891a737d 100644
--- a/cores/esp32/WMath.cpp
+++ b/cores/esp32/WMath.cpp
@@ -37,10 +37,23 @@ void randomSeed(unsigned long seed)
 
 long random(long howbig)
 {
-    if(howbig == 0) {
-        return 0;
+    uint32_t x = esp_random();
+    uint64_t m = uint64_t(x) * uint64_t(howbig);
+    uint32_t l = uint32_t(m);
+    if (l < howbig) {
+        uint32_t t = -howbig;
+        if (t >= howbig) {
+            t -= howbig;
+            if (t >= howbig) 
+                t %= howbig;
+        }
+        while (l < t) {
+            x = esp_random();
+            m = uint64_t(x) * uint64_t(howbig);
+            l = uint32_t(m);
+        }
     }
-    return esp_random() % howbig;
+    return m >> 32;
 }
 
 long random(long howsmall, long howbig)