Add a new module implementing a queue data structure.

Since the functions are simple make them inline functions. This provides a
small code size saving.

module_queue/src/queue.h

@@ -0,0 +1,54 @@
+#ifndef QUEUE_H_
+#define QUEUE_H_
+
+#include <xassert.h>
+
+typedef struct queue_t {
+    /// Read index.
+    unsigned rdptr;
+    /// Write index.
+    unsigned wrptr;
+    unsigned size;
+    unsigned mask;
+} queue_t;
+
+inline int is_power_of_2(unsigned x) {
+    return x != 0 && (x & (x - 1)) == 0;
+}
+
+inline void queue_init(queue_t &q, unsigned size) {
+    assert(is_power_of_2(size));
+    q.rdptr = 0;
+    q.wrptr = 0;
+    q.size = size;
+    q.mask = size - 1; // Assumes power of two.
+}
+
+inline int queue_is_empty(const queue_t &q) {
+    return q.wrptr == q.rdptr;
+}
+
+inline int queue_is_full(const queue_t &q) {
+    return q.wrptr - q.rdptr == q.size;
+}
+
+inline void queue_push_word(queue_t &q, unsigned array[], unsigned data)
+{
+    assert(!queue_is_full(q));
+    array[q.wrptr++ & q.mask] = data;
+}
+
+inline unsigned queue_pop_word(queue_t &q, unsigned array[]) {
+    assert(!queue_is_empty(q));
+    return array[q.rdptr++ & q.mask];
+}
+
+inline unsigned queue_items(const queue_t &q) {
+    return q.wrptr - q.rdptr;
+}
+
+inline unsigned queue_space(const queue_t &q) {
+    return q.size - queue_items(q);
+}
+
+#endif /* QUEUE_H_ */

module_queue/src/queue.xc

@@ -0,0 +1,11 @@
+#include "queue.h"
+
+// Force external definitions of inline functions.
+extern inline int is_power_of_2(unsigned x);
+extern inline void queue_init(queue_t &q, unsigned size);
+extern inline int queue_is_empty(const queue_t &q);
+extern inline int queue_is_full(const queue_t &q);
+extern inline void queue_push_word(queue_t &q, unsigned array[], unsigned data);
+extern inline unsigned queue_pop_word(queue_t &q, unsigned array[]);
+extern inline unsigned queue_space(const queue_t &q);
+extern inline unsigned queue_items(const queue_t &q);