Improved x64 encoder

src/build/arch/x64/encodeNum.go

@@ -0,0 +1,14 @@
+package x64
+
+import "encoding/binary"
+
+// encodeNum encodes an instruction with up to two registers and a number parameter.
+func encodeNum(code []byte, w byte, mod byte, reg byte, rm byte, number int, opCode8 byte, opCode32 byte) []byte {
+	if SizeOf(int64(number)) == 1 {
+		code = encode(code, w, mod, reg, rm, opCode8)
+		return append(code, byte(number))
+	}
+
+	code = encode(code, w, mod, reg, rm, opCode32)
+	return binary.LittleEndian.AppendUint32(code, uint32(number))
+}