The MySQL Protocol has a set of possible encodings for integers:
A fixed-length integer stores its value in a series of bytes with the least significant byte first.
A int<3> with the value
1 is stored as:
01 00 00
An integer that consumes 1, 3, 4, or 9 bytes, depending on its numeric value
To convert a number value into a length-encoded integer:
If the value is < 251, it is stored as a 1-byte integer.
If the value is ≥ 251 and <
(216), it is stored as
fc + 2-byte integer.
If the value is ≥ (216)
and < (224), it is stored
fd + 3-byte integer.
If the value is ≥ (224)
and < (264) it is stored
fe + 8-byte integer.
Up to MySQL 3.22,
0xfe was followed by
a 4-byte integer.
To convert a length-encoded integer into its numeric value, check the first byte:
If it is < 0xfb, treat it as a 1-byte integer.
If it is 0xfc, it is followed by a 2-byte integer.
If it is 0xfd, it is followed by a 3-byte integer.
If it is 0xfe, it is followed by a 8-byte integer.
If the first byte of a packet is a length-encoded integer
and its byte value is
0xfe, you must
check the length of the packet to verify that it has
enough space for a 8-byte integer.
If not, it may be an
Depending on the context, the first byte may also have other meanings:
0xff as the first byte of a
length-encoded integer is undefined.
fa -- 250 fc fb 00 -- 251