Working

bertos/algo/rle.c

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+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos 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 2 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2004 Develer S.r.l. (http://www.develer.com/)
+ * Copyright 1999, 2000, 2001 Bernie Innocenti <bernie@codewiz.org>
+ *
+ * -->
+ *
+ * \brief General-purpose run-length {en,de}coding algorithm (implementation)
+ *
+ * Original source code from http://www.compuphase.com/compress.htm
+ *
+ * \author Bernie Innocenti <bernie@codewiz.org>
+ */
+
+#include "rle.h"
+
+
+/**
+ * Run-length encode \a len bytes from the \a input buffer
+ * to the \a output buffer.
+ */
+int rle(unsigned char *output, const unsigned char *input, int len)
+{
+	int count, index, i;
+	unsigned char first;
+	unsigned char *out;
+
+
+	out = output;
+	count = 0;
+	while (count < len)
+	{
+		index = count;
+		first = input[index++];
+
+		/* Scan for bytes identical to the first one */
+		while ((index < len) && (index - count < 127) && (input[index] == first))
+			index++;
+
+		if (index - count == 1)
+		{
+			/* Failed to "replicate" the current byte. See how many to copy.
+			 */
+			while ((index < len) && (index - count < 127))
+			{
+				/* Avoid a replicate run of only 2-bytes after a literal run.
+				 * There is no gain in this, and there is a risc of loss if the
+				 * run after the two identical bytes is another literal run.
+				 * So search for 3 identical bytes.
+				 */
+				if ((input[index] == input[index - 1]) &&
+					((index > 1) && (input[index] == input[index - 2])))
+				{
+					/* Reset the index so we can back up these three identical
+					 * bytes in the next run.
+					 */
+					index -= 2;
+					break;
+				}
+
+				index++;
+			}
+
+			/* Output a run of uncompressed bytes: write length and values */
+			*out++ = (unsigned char)(count - index);
+			for (i = count; i < index; i++)
+				*out++ = input[i];
+	    }
+		else
+		{
+			/* Output a compressed run: write length and value */
+			*out++ = (unsigned char)(index - count);
+			*out++ = first;
+	    }
+
+		count = index;
+	}
+
+	/* Output EOF marker */
+	*out++ = 0;
+
+	return (out - output);
+}
+
+
+/**
+ * Run-length decode from the \a input buffer to the \a output
+ * buffer.
+ *
+ * \note The output buffer must be large enough to accomodate
+ *       all decoded output.
+ */
+int unrle(unsigned char *output, const unsigned char *input)
+{
+	signed char count;
+	unsigned char *out;
+	unsigned char value;
+
+
+	out = output;
+
+	for (;;)
+	{
+		count = (signed char)*input++;
+		if (count > 0)
+		{
+			/* replicate run */
+			value = *input++;
+			while (count--)
+				*out++ = value;
+		}
+		else if (count < 0)
+		{
+			/* literal run */
+			while (count++)
+				*out++ = *input++;
+		}
+		else
+			/* EOF */
+			break;
+	}
+
+	return (out - output);
+}