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authorDavid Woodhouse <dwmw2@shinybook.infradead.org>2006-04-11 19:09:16 -0400
committerDavid Woodhouse <dwmw2@shinybook.infradead.org>2006-04-11 19:09:16 -0400
commit72212c137c574b564723327af751c4054c7cfca6 (patch)
tree13be2da9d4be695002d6ea9c396660c986e5fa5c /compr_rtime.c
Initial commit
Diffstat (limited to 'compr_rtime.c')
-rw-r--r--compr_rtime.c122
1 files changed, 122 insertions, 0 deletions
diff --git a/compr_rtime.c b/compr_rtime.c
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+++ b/compr_rtime.c
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+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright (C) 2001-2003 Red Hat, Inc.
+ *
+ * Created by Arjan van de Ven <arjanv@redhat.com>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ * $Id: compr_rtime.c,v 1.4 2005/11/07 11:15:09 gleixner Exp $
+ *
+ *
+ * Very simple lz77-ish encoder.
+ *
+ * Theory of operation: Both encoder and decoder have a list of "last
+ * occurrences" 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 <stdint.h>
+#include <string.h>
+#include "compr.h"
+
+/* _compress returns the compressed size, -1 if bigger */
+static int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out,
+ uint32_t *sourcelen, uint32_t *dstlen, void *model)
+{
+ short 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;
+}
+
+
+static int jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out,
+ uint32_t srclen, uint32_t destlen, void *model)
+{
+ short 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;
+ }
+ }
+ }
+ return 0;
+}
+
+
+static struct jffs2_compressor jffs2_rtime_comp = {
+ .priority = JFFS2_RTIME_PRIORITY,
+ .name = "rtime",
+ .disabled = 0,
+ .compr = JFFS2_COMPR_RTIME,
+ .compress = &jffs2_rtime_compress,
+ .decompress = &jffs2_rtime_decompress,
+};
+
+int jffs2_rtime_init(void)
+{
+ return jffs2_register_compressor(&jffs2_rtime_comp);
+}
+
+void jffs2_rtime_exit(void)
+{
+ jffs2_unregister_compressor(&jffs2_rtime_comp);
+}