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engines/glk/scott/ring_buffer.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/*
+ * Based on ScottFree interpreter version 1.14 developed by Swansea
+ * University Computer Society without disassembly of any other game
+ * drivers, only of game databases as permitted by EEC law (for purposes
+ * of compatibility).
+ *
+ * Licensed under GPLv2
+ *
+ * https://github.com/angstsmurf/spatterlight/tree/master/terps/scott
+ */
+
+#include "glk/scott/ring_buffer.h"
+
+namespace Glk {
+namespace Scott {
+
+// The hidden definition of our circular buffer structure
+struct CircularBuf {
+	uint8_t *_buffer;
+	size_t _head;
+	size_t _tail;
+	size_t _max; // of the buffer
+	bool _full;
+};
+
+// Return a pointer to a struct instance
+cbuf_handle_t circularBufInit(uint8_t *buffer, size_t size) {
+	cbuf_handle_t cbuf = new CircularBuf;
+	cbuf->_buffer = buffer;
+	cbuf->_max = size;
+	circularBufReset(cbuf);
+
+	return cbuf;
+}
+
+void circularBufReset(cbuf_handle_t me) {
+	me->_head = 0;
+	me->_tail = 0;
+	me->_full = false;
+}
+
+void circularBufFree(cbuf_handle_t me) {
+	delete me;
+}
+
+bool circularBufFull(cbuf_handle_t me) {
+	return me->_full;
+}
+
+bool circularBufEmpty(cbuf_handle_t me) {
+	return (!me->_full && (me->_head == me->_tail));
+}
+
+size_t circularBufCapacity(cbuf_handle_t me) {
+	return me->_max;
+}
+
+size_t circularBufSize(cbuf_handle_t me) {
+	size_t size = me->_max;
+
+	if (!me->_full) {
+		if (me->_head >= me->_tail) {
+			size = (me->_head - me->_tail);
+		} else {
+			size = (me->_max + me->_head - me->_tail);
+		}
+	}
+
+	return size;
+}
+
+static void advancePointer(cbuf_handle_t me) {
+	if (me->_full) {
+		if (++(me->_tail) == me->_max) {
+			me->_tail = 0;
+		}
+	}
+
+	if (++(me->_head) == me->_max) {
+		me->_head = 0;
+	}
+	me->_full = (me->_head == me->_tail);
+}
+
+static void retreatPointer(cbuf_handle_t me) {
+
+	me->_full = false;
+	if (++(me->_tail) == me->_max) {
+		me->_tail = 0;
+	}
+}
+
+int circularBufPut(cbuf_handle_t me, uint8_t x, uint8_t y) {
+	int r = -1;
+
+	if (!circularBufFull(me)) {
+		me->_buffer[me->_head] = x;
+		advancePointer(me);
+		if (!circularBufFull(me)) {
+			me->_buffer[me->_head] = y;
+			advancePointer(me);
+			r = 0;
+		}
+	}
+	return r;
+}
+
+int circularBufGet(cbuf_handle_t me, int *x, int *y) {
+	int r = -1;
+
+	if (!circularBufEmpty(me)) {
+		*x = me->_buffer[me->_tail];
+		retreatPointer(me);
+		if (!circularBufEmpty(me)) {
+			*y = me->_buffer[me->_tail];
+			retreatPointer(me);
+			r = 0;
+		}
+	}
+	return r;
+}
+
+} // End of namespace Scott
+} // End of namespace Glk