From e928e20b11b897a818265b27cb431b1a2c6df181 Mon Sep 17 00:00:00 2001
From: Tom Pittenger <magicrub@gmail.com>
Date: Mon, 19 Sep 2016 02:42:06 -0700
Subject: [PATCH] AP_RangeFinder: Ensure no divide by zeros in LeddarOne

Having a critical divide by value as a class member that could change external to the function using it is fragile. It was not very obvious that a divide by zero was not possible in the current design, now it's very obvious and safer in case the code changes later.
---
 .../AP_RangeFinder/AP_RangeFinder_LeddarOne.cpp      | 12 ++++++++----
 libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.h  |  1 -
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.cpp
index 1ed812b023..3313e1f3aa 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.cpp
@@ -68,12 +68,16 @@ bool AP_RangeFinder_LeddarOne::get_reading(uint16_t &reading_cm)
     }
 
     // parse a response message, set detections and sum_distance
-    if (parse_response() <= 0) {
+    // must be signed to handle errors
+    int8_t number_detections = parse_response();
+
+    if (number_detections <= 0) {
+        // TODO: when (number_detections < 0) handle LEDDARONE_ERR_
         return false;
     }
 
     // calculate average distance
-    reading_cm = sum_distance / number_detections;
+    reading_cm = sum_distance / (uint8_t)number_detections;
 
     return true;
 }
@@ -204,7 +208,7 @@ int8_t AP_RangeFinder_LeddarOne::parse_response(void)
     }
 
     // number of detections
-    number_detections = data_buffer[10];
+    uint8_t number_detections = data_buffer[10];
 
     // if the number of detection is over , it is false
     if (number_detections > (sizeof(detections) / sizeof(detections[0]))) {
@@ -220,5 +224,5 @@ int8_t AP_RangeFinder_LeddarOne::parse_response(void)
         index_offset += 4;
     }
 
-    return number_detections;
+    return (int8_t)number_detections;
 }
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.h b/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.h
index 264cacfa91..4933fddcc2 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_LeddarOne.h
@@ -47,6 +47,5 @@ private:
     uint32_t last_reading_ms = 0;
 
     uint16_t detections[3];
-    uint8_t number_detections = 0;
     uint32_t sum_distance = 0;
 };