patch-2.4.10 linux/fs/jffs2/compr_rtime.c

• Lines: 129
• Date: Fri Sep 14 14:04:07 2001
• Orig file: v2.4.9/linux/fs/jffs2/compr_rtime.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.9/linux/fs/jffs2/compr_rtime.c linux/fs/jffs2/compr_rtime.c
@@ -0,0 +1,128 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright (C) 2001 Red Hat, Inc.
+ *
+ * Created by Arjan van de Ven <arjanv@redhat.com>
+ *
+ * The original JFFS, from which the design for JFFS2 was derived,
+ * was designed and implemented by Axis Communications AB.
+ *
+ * The contents of this file are subject to the Red Hat eCos Public
+ * License Version 1.1 (the "Licence"); you may not use this file
+ * except in compliance with the Licence.  You may obtain a copy of
+ * the Licence at http://www.redhat.com/
+ *
+ * Software distributed under the Licence is distributed on an "AS IS"
+ * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.
+ * See the Licence for the specific language governing rights and
+ * limitations under the Licence.
+ *
+ * The Original Code is JFFS2 - Journalling Flash File System, version 2
+ *
+ * Alternatively, the contents of this file may be used under the
+ * terms of the GNU General Public License version 2 (the "GPL"), in
+ * which case the provisions of the GPL are applicable instead of the
+ * above.  If you wish to allow the use of your version of this file
+ * only under the terms of the GPL and not to allow others to use your
+ * version of this file under the RHEPL, indicate your decision by
+ * deleting the provisions above and replace them with the notice and
+ * other provisions required by the GPL.  If you do not delete the
+ * provisions above, a recipient may use your version of this file
+ * under either the RHEPL or the GPL.
+ *
+ * $Id: compr_rtime.c,v 1.5 2001/03/15 15:38:23 dwmw2 Exp $
+ *
+ *
+ * Very simple lz77-ish encoder.
+ *
+ * Theory of operation: Both encoder and decoder have a list of "last
+ * occurances" for every possible source-value; after sending the
+ * first source-byte, the second byte indicated the "run" length of
+ * matches
+ *
+ * The algorithm is intended to only send "whole bytes", no bit-messing.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/string.h> 
+
+/* _compress returns the compressed size, -1 if bigger */
+int rtime_compress(unsigned char *data_in, unsigned char *cpage_out, 
+		   __u32 *sourcelen, __u32 *dstlen)
+{
+	int positions[256];
+	int outpos = 0;
+	int pos=0;
+
+	memset(positions,0,sizeof(positions)); 
+	
+	while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
+		int backpos, runlen=0;
+		unsigned char value;
+		
+		value = data_in[pos];
+
+		cpage_out[outpos++] = data_in[pos++];
+		
+		backpos = positions[value];
+		positions[value]=pos;
+		
+		while ((backpos < pos) && (pos < (*sourcelen)) &&
+		       (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
+			pos++;
+			runlen++;
+		}
+		cpage_out[outpos++] = runlen;
+	}
+
+	if (outpos >= pos) {
+		/* We failed */
+		return -1;
+	}
+	
+	/* Tell the caller how much we managed to compress, and how much space it took */
+	*sourcelen = pos;
+	*dstlen = outpos;
+	return 0;
+}		   
+
+
+void rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
+		      __u32 srclen, __u32 destlen)
+{
+	int positions[256];
+	int outpos = 0;
+	int pos=0;
+	
+	memset(positions,0,sizeof(positions)); 
+	
+	while (outpos<destlen) {
+		unsigned char value;
+		int backoffs;
+		int repeat;
+		
+		value = data_in[pos++];
+		cpage_out[outpos++] = value; /* first the verbatim copied byte */
+		repeat = data_in[pos++];
+		backoffs = positions[value];
+		
+		positions[value]=outpos;
+		if (repeat) {
+			if (backoffs + repeat >= outpos) {
+				while(repeat) {
+					cpage_out[outpos++] = cpage_out[backoffs++];
+					repeat--;
+				}
+			} else {
+				memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
+				outpos+=repeat;		
+			}
+		}
+	}		
+}		   
+
+