1 files changed, 213 insertions, 0 deletions
diff --git a/src/lzw.cpp b/src/lzw.cpp
new file mode 100644
index 00000000..52ca569d
--- /dev/null
+++ b/src/lzw.cpp
@@ -0,0 +1,213 @@
+#include <string.h>
+
+// LZW Compressor
+struct SYM
+{
+	unsigned char data[1024*2];
+	int size;
+	int next;
+};
+
+struct SYMBOLS
+{
+	SYM syms[512];
+	int jumptable[256];
+	int currentsym;
+};
+
+static SYMBOLS symbols;
+
+// symbol info
+inline int sym_size(int i) { return symbols.syms[i].size; }
+inline unsigned char *sym_data(int i) { return symbols.syms[i].data; }
+
+static void sym_init()
+{
+	for(int i = 0; i < 256; i++)
+	{
+		symbols.syms[i].data[0] = (unsigned char)i;
+		symbols.syms[i].size = 1;
+		symbols.jumptable[i] = -1;
+	}
+
+	for(int i = 0; i < 512; i++)
+		symbols.syms[i].next = -1;
+
+	symbols.currentsym = 0;
+}
+
+static void sym_index(int sym)
+{
+	int table = symbols.syms[sym].data[0];
+	symbols.syms[sym].next = symbols.jumptable[table];
+	symbols.jumptable[table] = sym;
+}
+
+static void sym_unindex(int sym)
+{
+	int table = symbols.syms[sym].data[0];
+	int prev = -1;
+	int current = symbols.jumptable[table];
+
+	while(current != -1)
+	{
+		if(current == sym)
+		{
+			if(prev != -1)
+				symbols.syms[prev].next = symbols.syms[current].next;
+			else
+				symbols.jumptable[table] = symbols.syms[current].next;
+			break;
+		}
+
+		prev = current;
+		current = symbols.syms[current].next;
+	}
+}
+
+static int sym_add(unsigned char *sym, long len)
+{
+	int i = 256+symbols.currentsym;
+
+	memcpy(symbols.syms[i].data, sym, len);
+	symbols.syms[i].size = len;
+	symbols.currentsym = (i+1)%255;
+	return i;
+}
+
+static int sym_add_and_index(unsigned char *sym, long len)
+{
+	if(symbols.syms[256+symbols.currentsym].size)
+		sym_unindex(256+symbols.currentsym);
+	int s = sym_add(sym, len);
+	sym_index( s);
+	return s;
+}
+
+static void sym_append(int sym, unsigned char extra)
+{
+	symbols.syms[sym].data[symbols.syms[sym].size] = extra;
+	symbols.syms[sym].size++;
+}
+
+static int sym_find(unsigned char *data, int size)
+{
+	int best = data[0];
+	int bestlen = 1;
+	int current = symbols.jumptable[data[0]];
+
+	while(current != -1)
+	{
+		if(symbols.syms[current].size <= size && memcmp(data, symbols.syms[current].data, symbols.syms[current].size) == 0)
+		{
+			if(bestlen < symbols.syms[current].size)
+			{
+				bestlen = symbols.syms[current].size;
+				best = current;
+			}
+		}
+
+		current = symbols.syms[current].next;
+	}		
+
+	return best;
+}
+
+//
+// compress
+//
+long lzw_compress(const void *src_, int size, void *dst_)
+{
+	unsigned char *src = (unsigned char *)src_;
+	unsigned char *end = (unsigned char *)src_+size;
+	unsigned char *dst = (unsigned char *)dst_;
+	long left = (end-src);
+
+	// init symboltable
+	sym_init();
+
+	bool done = false;
+	while(!done)
+	{
+		unsigned char *flagptr = dst;
+		unsigned char flagbits = 0;
+		int b = 0;
+
+		dst++; // skip a byte where the flags are
+
+		for(; b < 8; b++)
+		{
+			if(left <= 0) // check for EOF
+			{
+				// write EOF symbol
+				flagbits |= 1<<b;
+				*dst++ = 255;
+				done = true;
+				break;
+			}
+
+ 			int sym = sym_find( src, left);
+			int symsize = sym_size( sym);
+
+			if(sym&0x100)
+				flagbits |= 1<<b; // add bit that says that its a symbol
+
+			*dst++ = sym&0xff; // set symbol
+
+			if(left > symsize+1) // create new symbol
+				sym_add_and_index( src, symsize+1);
+			
+			src += symsize; // advance src
+			left -= symsize;
+		}
+
+		// write the flags
+		*flagptr = flagbits;
+	}
+
+	return (long)(dst-(unsigned char*)dst_);
+}
+
+//
+// decompress
+//
+long lzw_decompress(const void *src_, void *dst_)
+{
+	unsigned char *src = (unsigned char *)src_;
+	unsigned char *dst = (unsigned char *)dst_;
+	int previtem = -1; // 0-255 = raw byte, 256+ = symbol
+	int item;
+
+	sym_init();
+
+	while(1)
+	{
+		unsigned char flagbits = 0;
+		flagbits = *src++; // read flags
+
+		int b = 0;
+		for(; b < 8; b++)
+		{
+			item = *src++;
+			if(flagbits&(1<<b))
+				item |= 256;
+
+			if(item == 0x1ff) // EOF symbol
+				return (dst-(unsigned char *)dst_);
+
+			if(previtem != -1) // this one could be removed
+			{
+				// the previous item can 
+				int s = sym_add( sym_data( previtem), sym_size( previtem));
+				sym_append(s, sym_data( item)[0]);
+			}
+				
+			memcpy(dst, sym_data( item), sym_size( item));
+			dst += sym_size( item);
+			previtem = item;
+		}
+
+	}
+
+	return 0;
+}