====== Data Types for the AMF Data Format ======

{{tag>documentation amf datatype}}

AMF has core data types that are there every step of the way for serializing data. These should not be confused with the [[documentation:amf:astypes|AMF actionscript data types]]. The core data types include:

  * Byte
  * Int
  * MediumInt
  * Long
  * Double
  * UTF8
  * LongUTF8

An AMF **Byte** is the simplest data type to read and write.  It is simply an 8-bit byte.

An AMF **Int** is made up of 2 consecutive bytes. It represents a 16-bit number. The first byte in the file/stream is the most significant bit and the second byte in the file/stream is the LSB.

An AMF **MediumInt** is made up of 3 consecutive bytes. It represents a 24-bit number. The first byte in the file/stream is the most significant bit and the third byte in the file/stream is the LSB. MediumInt's appear to be used exclusively by FlashCom.

The AMF **Long** is made up of 4 consecutive bytes. It represents a 32-bit number. Like the Int and MediumInt, it is unsigned and the LSB is on the right.

The AMF **Double** is made up of 8 consecutive bytes. It represents a floating point, signed number. The double is little-endian encoded. In PHP a double can be read in the following way (this should also work for any language that has a pack function):

<code php>
$bytes = substr($this->raw_data, $this->current_byte, 8);
$this->current_byte += 8;
if ($this->isBigEndian) {
     $bytes = strrev($bytes);
} 
$zz = unpack("dflt", $bytes); // unpack the bytes
return $zz['flt']; // return the number from the associative array
</code>

The AMF **UTF8** represents a string shorter than 2^16 bytes. It is composed of an Int (2 bytes) representing string length followed by the UTF8-encoded string.

The AMF **LongUTF8** represents a string potentially longer than 2^16 bytes. It is composed of an LongInt (4 bytes) representing string length followed by the UTF8-encoded string.