/**
* compute a frequency table from an InputStream and save a compacted representation of this table
* in the system preferences. (To be used later by @see #useStandardTable(String) )
*
* @param name name to give the table.
* @param in InputStream
* @return true on success
* @throws Exception
*/
public static boolean CreateStandardTableFromStream(String name, InputStream in)
throws Exception {
int[] tbl = new int[TABLESIZE];
while (in.available() != 0) {
int c = in.read();
tbl[c]++;
}
byte[] dest = HuffmanTree.compactTable(tbl);
Preferences pref = Preferences.userNodeForPackage(Huff.class);
Preferences node = pref.node("StandardTables");
node.putByteArray(name, dest);
pref.flush();
return true;
}
/**
* compress the source array. use rllchar as character to indicate repetition. if rllchar is 0x0,
* the least frequent character from source will be used.
*
* @return a newly created array with the rll compressed data.
*/
public static byte[] compress(byte rllchar, byte[] source) {
if (rllchar == (byte) 0) {
int[] freq = HuffmanTree.constructTable(source);
int min = 100000;
for (int i = 0; i < freq.length; i++) {
if (freq[i] == 0) {
rllchar = (byte) i;
break;
}
if (freq[i] < min) {
min = freq[i];
rllchar = (byte) i;
}
}
}
ByteArrayOutputStream baos = new ByteArrayOutputStream(source.length);
baos.write(rllchar);
int i;
for (i = 0; i < source.length - 3; i++) {
if ((source[i] == source[i + 1]) && (source[i + 1] == source[i + 2])) {
int rep = 3;
while (((i + rep) < source.length) && source[i + rep] == source[i]) {
if (rep == 254) break;
rep++;
}
baos.write(rllchar);
baos.write(rep);
baos.write(source[i]);
i += rep - 1;
} else if (source[i] == rllchar) {
baos.write(rllchar);
baos.write(1);
} else {
baos.write(source[i]);
}
}
while (i < source.length) {
baos.write(source[i++]);
}
return baos.toByteArray();
}
/**
* Import a compaced frequency table from the system preferences (In windows from the registry
* HKLM/JavaSoft/Prefs/ch/rgw/tools/Compress/StandardTables, in Linux from ~/.prefs)
*
* @param name Name of the table in the registry. If no table with this name is found, the default
* table (TextDeutsch) is returned.
* @return the table
*/
public static int[] useStandardTable(String name) {
Preferences pr = Preferences.userNodeForPackage(Huff.class);
Preferences node = pr.node("StandardTables");
byte[] res = node.getByteArray(name, TextDeutsch);
return HuffmanTree.expandTable(res);
}
