Added macro to calculate the next power of two for FIFO data store (#69)

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/basic/sys/fifo.c

@@ -45,7 +45,7 @@
  *
  * To use this library, first declare a data store, sized for a power of 2:
  * {@code
- * static volatile uint8_t data_store[64];
+ * static volatile FIFO_DATA_STORE(data_store, 64);
  * }
  *
  * Then declare the FIFO tracking structure:
@@ -343,8 +343,7 @@ void testFIFOBuffer(Test *pTest)
 {
     /* FIFO data structure */
     FIFO_BUFFER test_buffer = { 0 };
-    /* FIFO data store. Note:  size must be a power of two! */
+    volatile FIFO_DATA_STORE(data_store, 60) = { 0 };
-    volatile uint8_t data_store[64] = { 0 };
     uint8_t add_data[40] = { "RoseSteveLouPatRachelJessicaDaniAmyHerb" };
     uint8_t test_add_data[40] = { 0 };
     uint8_t test_data = 0;
@@ -352,6 +351,7 @@ void testFIFOBuffer(Test *pTest)
     unsigned count = 0;
     bool status = 0;
 
+    ct_test(pTest, sizeof(data_store) == 64);
     FIFO_Init(&test_buffer, data_store, sizeof(data_store));
     ct_test(pTest, FIFO_Empty(&test_buffer));
 

src/bacnet/basic/sys/fifo.h

@@ -10,6 +10,29 @@
 #include <stdbool.h>
 #include "bacnet/bacnet_stack_exports.h"
 
+/**
+* FIFO buffer power of two alignment macro
+*
+* @{
+*/
+#ifndef NEXT_POWER_OF_2
+#define B2(x)    (   (x) | (   (x) >> 1) )
+#define B4(x)    ( B2(x) | ( B2(x) >> 2) )
+#define B8(x)    ( B4(x) | ( B4(x) >> 4) )
+#define B16(x)   ( B8(x) | ( B8(x) >> 8) )
+#define B32(x)   (B16(x) | (B16(x) >>16) )
+#define NEXT_POWER_OF_2(x) (B32((x)-1) + 1)
+#endif
+/** @} */
+
+/**
+* FIFO data store structure
+*
+* @{
+*/
+#define FIFO_DATA_STORE(b,c) uint8_t b[NEXT_POWER_OF_2(c)]
+/** @} */
+
 /**
 * FIFO data structure
 *