Fix FIFObuffer::get()

- Prevent actual_index being calculated as negative

Add test_FIFObuffer_push_and_get

Author: danverstom

README.md

@@ -8,9 +8,6 @@ Changes made:
 - Added extra methods
 - You can change the type and size of the buffer
 
-Known issues/TODO:
-- `FIFObuffer::get()` doesn't work properly
-
 # Explanation
 
 https://en.wikipedia.org/wiki/FIFO_(computing_and_electronics)

platformio.ini

@@ -2,4 +2,5 @@
 build_flags = -std=c++14
 
 [env:native]
-platform = native
+platform = native
+debug_test = *

src/FIFObuffer.cpp

@@ -114,7 +114,9 @@ void FIFObuffer<T, FIFOsize>::clear() {
 
 template<typename T, int FIFOsize>
 T FIFObuffer<T, FIFOsize>::get(int index) {
-    int actual_index = (tail - index) % FIFOsize;
+    // we add FIFOsize to (tail - index) to make sure actual_index never goes negative
+    // as you can't have a negative index of an array
+    int actual_index = (FIFOsize + tail - index) % FIFOsize;
     return buffer[actual_index];
 }
 

test/test_FIFObuffer.cpp

@@ -64,8 +64,13 @@ void test_FIFObuffer_sum() {
     FIFObuffer<int, 3> buffer;
     buffer.put(1);
     buffer.put(2);
-    buffer.put(3);
+    buffer.push(3);
     TEST_ASSERT_EQUAL(6, buffer.sum());
+
+    FIFObuffer<int, 3> buffer2;
+    buffer2.put(1);
+    buffer2.put(2);
+    TEST_ASSERT_EQUAL(3, buffer2.sum());
 }
 
 void test_FIFObuffer_clear() {
@@ -79,17 +84,27 @@ void test_FIFObuffer_clear() {
     TEST_ASSERT_EQUAL(10, buffer.sum());
 }
 
+void test_FIFObuffer_push_and_get() {
+    FIFObuffer<int, 2> buffer;
+    buffer.put(0);
+    buffer.put(1);
+    buffer.push(2);
+    TEST_ASSERT_EQUAL(2, buffer.get(0));
+    TEST_ASSERT_EQUAL(1, buffer.get(1));
+}
+
 int main(int args, char **argv) {
     UNITY_BEGIN();
-
+    RUN_TEST(test_FIFObuffer_push_and_get);
     RUN_TEST(test_FIFObuffer_count);
     RUN_TEST(test_FIFObuffer_full_empty);
     RUN_TEST(test_FIFObuffer_order);
     RUN_TEST(test_FIFObuffer_put);
     RUN_TEST(test_FIFObuffer_push);
-    RUN_TEST(test_FIFObuffer_get);
     RUN_TEST(test_FIFObuffer_sum);
     RUN_TEST(test_FIFObuffer_clear);
+    RUN_TEST(test_FIFObuffer_get);
+
 
     UNITY_END();