From ff035c8b08a863ca22ff95ca93d735f237e9ee8a Mon Sep 17 00:00:00 2001
From: Russell Gallop <russell@xmos.com>
Date: Thu, 11 Aug 2011 15:39:49 +0100
Subject: [PATCH] Add queue implementation from experiments area.

---
 module_usb_midi/src/queue.c | 48 +++++++++++++++++++++++++++++++++++++
 module_usb_midi/src/queue.h | 24 +++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 module_usb_midi/src/queue.c
 create mode 100644 module_usb_midi/src/queue.h

diff --git a/module_usb_midi/src/queue.c b/module_usb_midi/src/queue.c
new file mode 100644
index 00000000..90602c33
--- /dev/null
+++ b/module_usb_midi/src/queue.c
@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include "queue.h"
+
+// This presumes that the xc compiler will not re-use the mem passed to init_queue
+void init_queue(queue *q, int arr[], int size) {
+   q->rdptr = 0;
+   q->wrptr = 0;
+   q->data = (intptr_t)arr;
+   q->size = size; // presume that size is power of two
+   q->mask = size - 1;
+}
+
+extern inline void enqueue(queue *q, int value) {
+   ((int *)q->data)[q->wrptr & q->mask] = value;
+   q->wrptr++;
+}
+
+extern inline int dequeue(queue *q) {
+   int retval = ((int *)q->data)[q->rdptr & q->mask];
+   q->rdptr++;
+   return retval;
+}
+
+extern inline int isempty(queue *q) {
+   return (q->rdptr == q->wrptr);
+}
+
+extern inline int isfull(queue *q) {
+   return ((q->wrptr - q->rdptr) == q->size);
+}
+
+extern inline int items(queue *q) {
+   int items = q->wrptr - q->rdptr;
+   return items;
+}
+
+// How to calculate size? Could make it a function call or leave it as a variable within the struct
+extern inline int space(queue *q) {
+   return q->size - items(q);
+}
+
+void dump(queue *q) {
+   for (int i = q->rdptr; i != q->wrptr; i++) {
+      printf("a[%d] = %d\n", i & q->mask, ((int *)q->data)[i & q->mask]);
+   }
+}
+
+
diff --git a/module_usb_midi/src/queue.h b/module_usb_midi/src/queue.h
new file mode 100644
index 00000000..1e560ecf
--- /dev/null
+++ b/module_usb_midi/src/queue.h
@@ -0,0 +1,24 @@
+#ifndef QUEUE_H
+#define QUEUE_H
+
+#include <stdint.h>
+#include <xccompat.h>
+
+typedef struct queue {
+   intptr_t data;
+   int rdptr; // Using absolute indices which count reads and writes so this needs to be considered when accessing.
+   int wrptr;
+   int size;
+   int mask;
+} queue;
+
+void init_queue(REFERENCE_PARAM(queue, q), int arr[], int size);
+void enqueue(REFERENCE_PARAM(queue, q), int value);
+int dequeue(REFERENCE_PARAM(queue, q));
+int isempty(REFERENCE_PARAM(queue, q));
+int isfull(REFERENCE_PARAM(queue, q));
+int items(REFERENCE_PARAM(queue, q));
+int space(REFERENCE_PARAM(queue, q));
+void dump(REFERENCE_PARAM(queue, q));
+
+#endif // QUEUE_H