LibDEFLATE: Add GZip support

This allows compressing and decompressing with data using GZip headers
and footers

LibDEFLATE/include/LibDEFLATE/StreamType.h

@@ -7,6 +7,7 @@ namespace LibDEFLATE
 	{
 		Raw,
 		Zlib,
+		GZip,
 	};
 
 }

LibDEFLATE/include/LibDEFLATE/Utils.h

@@ -19,6 +19,25 @@ namespace LibDEFLATE
 		return (s2 << 16) | s1;
 	}
 
+	inline uint32_t calculate_crc32(BAN::ConstByteSpan data)
+	{
+		uint32_t crc32 = 0xFFFFFFFF;
+		uint32_t polynomial = 0xEDB88320;
+
+		for (size_t i = 0; i < data.size(); i++) {
+			crc32 ^= data[i];
+
+			for (size_t j = 0; j < 8; j++) {
+				if (crc32 & 1)
+					crc32 = (crc32 >> 1) ^ polynomial;
+				else
+					crc32 >>= 1;
+			}
+		}
+
+		return ~crc32;
+	}
+
 	inline constexpr uint16_t reverse_bits(uint16_t value, size_t count)
 	{
 		uint16_t reverse = 0;