Revert "drop mlz"

This reverts commit 4af1aa03b5d7f0d304ef30f9ffc92ec5ac6d6c22.

src/mame/sinclair/spec_snqk.cpp

@@ -2404,6 +2404,146 @@ void spectrum_state::setup_z80(const uint8_t *snapdata, uint32_t snapsize)
 	}
 }
 
+void spectrum_state::mlz_decompress_block(address_space &space, const u8 *source, u16 dest, u16 size)
+{
+	class de_mlz
+	{
+	private:
+		address_space &m_space;
+		const u8 *m_src;
+		u16 m_to;
+		u8 m_buffer;
+		int m_buffer_size;
+
+	public:
+		de_mlz(address_space &space, const u8 *src, u16 dst) : m_space(space)
+		{
+			m_src = src;
+			m_to = dst;
+		}
+
+		void init_bitstream()
+		{
+			m_buffer = get_byte();
+			m_buffer_size = 8;
+		}
+
+		u8 get_byte()
+		{
+			return *m_src++;
+		}
+
+		void put_byte(u8 val)
+		{
+			m_space.write_byte(m_to++, val);
+		}
+
+		void repeat(u32 disp, int num)
+		{
+			for (int i = 0; i < num; i++)
+			{
+				u8 val = m_space.read_byte(m_to - disp);
+				put_byte(val);
+			}
+		}
+
+		// gets specified number of bits from bitstream
+		// returns them LSB-aligned
+		u32 get_bits(int count)
+		{
+			u32 bits = 0;
+			while (count--)
+			{
+				if (m_buffer_size--)
+				{
+					bits <<= 1;
+					bits |= 1 & (m_buffer >> 7);
+					m_buffer <<= 1;
+				}
+				else
+				{
+					init_bitstream();
+					count++; // repeat loop once more
+				}
+			}
+
+			return bits;
+		}
+
+		int get_bigdisp()
+		{
+			u32 bits;
+
+			// inter displacement
+			if (get_bits(1))
+			{
+				bits = get_bits(4);
+				return 0x1100 - (bits << 8) - get_byte();
+			}
+
+			// shorter displacement
+			else
+				return 256 - get_byte();
+		}
+	};
+
+	de_mlz s(space, source, dest);
+	u32 done = 0;
+	int i;
+
+	// get first byte of packed file and write to output
+	s.put_byte(s.get_byte());
+
+	// second byte goes to bitstream
+	s.init_bitstream();
+
+	// actual depacking loop!
+	do
+	{
+		// get 1st bit - either OUTBYTE or beginning of LZ code
+		// OUTBYTE
+		if (s.get_bits(1))
+			s.put_byte(s.get_byte());
+
+		// LZ code
+		else
+		{
+			switch (s.get_bits(2))
+			{
+			case 0: // 000
+				s.repeat(8 - s.get_bits(3), 1);
+				break;
+
+			case 1: // 001
+				s.repeat(256 - s.get_byte(), 2);
+				break;
+
+			case 2: // 010
+				s.repeat(s.get_bigdisp(), 3);
+				break;
+
+			case 3: // 011
+				// extract num of length bits
+				for (i = 1; !s.get_bits(1); i++)
+					;
+
+				// check for exit code
+				if (i == 9)
+				{
+					done = 1;
+				}
+				else if (i <= 7)
+				{
+					// get length bits itself
+					int bits = s.get_bits(i);
+					s.repeat(s.get_bigdisp(), 2 + (1 << i) + bits);
+				}
+				break;
+			}
+		}
+	} while (!done);
+}
+
 /*
     Load a .SPG (Spectrum Prog) file.
 
@@ -2467,8 +2607,7 @@ void spectrum_state::setup_spg(const u8 *snapdata, u32 snapsize)
 				break;
 
 			case 0x01:
-				logerror("Unsupported MegaLZ compressed");
-				return;
+				mlz_decompress_block(space, &snapdata[data_offset], 0xc000 + offs, size);
 				break;
 
 			case 0x02:

src/mame/sinclair/spectrum.h

@@ -206,6 +206,7 @@ protected:
 	void setup_frz(const uint8_t *snapdata, uint32_t snapsize);
 	void z80_decompress_block(address_space &space, const uint8_t *source, uint16_t dest, uint16_t size);
 	void setup_z80(const uint8_t *snapdata, uint32_t snapsize);
+	void mlz_decompress_block(address_space &space, const u8 *source, u16 dest, u16 size);
 	void setup_spg(const u8 *snapdata, u32 snapsize);
 	// quickload helpers
 	void log_quickload(const char *type, uint32_t start, uint32_t length, uint32_t exec, const char *exec_format);