py/ringbuf.h: Add reusable ring buffer class.

Features inline get/put operations for the highest performance. Locking
is not part of implementation, operation should be wrapped with locking
externally as needed.

py/ringbuf.h

+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Paul Sokolovsky
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef __MICROPY_INCLUDED_PY_RINGBUF_H__
+#define __MICROPY_INCLUDED_PY_RINGBUF_H__
+
+typedef struct _ringbuf_t {
+    uint8_t *buf;
+    uint16_t size;
+    uint16_t iget;
+    uint16_t iput;
+} ringbuf_t;
+
+// Static initalization:
+// byte buf_array[N];
+// ringbuf_t buf = {buf_array, sizeof(buf_array)};
+
+// Dynamic initialization. This creates root pointer!
+#define ringbuf_alloc(r, sz) \
+{ \
+    (r)->buf = m_new(uint8_t, sz); \
+    (r)->size = sz; \
+    (r)->iget = (r)->iput = 0; \
+}
+
+static inline int ringbuf_get(ringbuf_t *r) {
+    if (r->iget == r->iput) {
+        return -1;
+    }
+    uint8_t v = r->buf[r->iget++];
+    if (r->iget >= r->size) {
+        r->iget = 0;
+    }
+    return v;
+}
+
+static inline int ringbuf_put(ringbuf_t *r, uint8_t v) {
+    uint32_t iput_new = r->iput + 1;
+    if (iput_new >= r->size) {
+        iput_new = 0;
+    }
+    if (iput_new == r->iget) {
+        return -1;
+    }
+    r->buf[r->iput] = v;
+    r->iput = iput_new;
+    return 0;
+}
+
+#endif // __MICROPY_INCLUDED_PY_RINGBUF_H__