Reduced the use of volatiles to speed up rb_insert() and rb_remove().

Added support for non-power-of-two ring buffers.

1 files changed, 15 insertions, 15 deletions

diff --git a/libmaple/ring_buffer.h b/libmaple/ring_buffer.h
index b4c136f..43e0b28 100644
--- a/libmaple/ring_buffer.h
+++ b/libmaple/ring_buffer.h
@@ -17,43 +17,43 @@ typedef struct ring_buffer {
     /** Buffer items are stored into */
     volatile uint8 *buf;
     /** Index of the next item to remove */
-    volatile uint16 head;
+    uint16 head;
     /** Index where the next item will get inserted */
-    volatile uint16 tail;
-    /** Buffer capacity */
+    uint16 tail;
+    /** Buffer capacity minus one */
     uint16 size;
 } ring_buffer;
 
 /** Initialise a ring buffer.
-
-    @param rb    instance to initialise
-    @param size  number of items in the buffer
-    @param buf   buffer to store items into
+ *
+ *  @param rb    instance to initialise
+ *  @param size  number of items in the buffer
+ *  @param buf   buffer to store items into
 */
-static inline void rb_init(ring_buffer *rb, uint8 size, uint8 *buf) {
-    ASSERT(IS_POWER_OF_TWO(size));
+static inline void rb_init(ring_buffer *rb, uint16 size, uint8 *buf) {
     rb->head = 0;
     rb->tail = 0;
-    rb->size = size;
+    rb->size = size - 1;
     rb->buf = buf;
 }
 
 /** Append an item onto the end of the ring buffer */
 static inline void rb_insert(ring_buffer *rb, uint8 element) {
-    rb->buf[(rb->tail)++] = element;
-    rb->tail &= (rb->size - 1);
+    rb->buf[rb->tail] = element;
+    rb->tail = (rb->tail == rb->size) ? 0 : rb->tail + 1;
 }
 
 /** Remove and return the first item from the ring buffer */
 static inline uint8 rb_remove(ring_buffer *rb) {
-    uint8 ch = rb->buf[rb->head++];
-    rb->head &= (rb->size - 1);
+    uint8 ch = rb->buf[rb->head];
+    rb->head = (rb->head == rb->size) ? 0 : rb->head + 1;
     return ch;
 }
 
 static inline uint32 rb_full_count(ring_buffer *rb) {
     /* PENDING: Broken */
-    return rb->tail - rb->head;
+    volatile ring_buffer *arb = rb;
+    return arb->tail - arb->head;
 }
 
 /** Discard all items from the buffer */