genmidi: Add Python code for reading OPL instruments.

These files load OPL instrument data from SBI (SoundBlaster Instrument)
or A2I (AdlibTracker2 Instrument) format files.

lumps/genmidi/sbi_file.py

@@ -0,0 +1,43 @@
+
+import struct
+import sys
+
+HEADER_VALUE = "SBI\x1a"
+
+FIELDS = [
+	"m_am_vibrato_eg",
+	"c_am_vibrato_eg",
+	"m_ksl_volume",
+	"c_ksl_volume",
+	"m_attack_decay",
+	"c_attack_decay",
+	"m_sustain_release",
+	"c_sustain_release",
+	"m_waveform",
+	"c_waveform",
+	"feedback_fm"
+]
+
+def read(filename):
+	f = open(filename)
+	data = f.read()
+	f.close()
+
+	header, name = struct.unpack("4s32s", data[0:36])
+
+	if header != HEADER_VALUE:
+		raise Exception("Invalid header for SBI file!")
+
+	instr_data = data[36:]
+	result = { "name": name.rstrip("\0") }
+
+	for i in range(len(FIELDS)):
+		result[FIELDS[i]], = struct.unpack("B", instr_data[i:i+1])
+
+	return result
+
+if __name__ == "__main__":
+	for filename in sys.argv[1:]:
+		print filename
+		print read(filename)
+