Offsets

The offsets group defines formulas for calculating offsets. It contains statements with the following syntax:

offset new_group = base_group+(field $<<$ shift)

new_offset

is the index of the new offset defined here. This number must be greater than zero.

base_offset

is the index of the offset the new offset is based on. base_offset has been defined earlier in the offsets group. A value of 0 means that the new offset is relative to the beginning of the packet.

field

describes the access to the field in the packet header containing the values used in the offset calculation. The field syntax is described in section 7.2.8.

shift

is the number of bits the value of field is shifted to the left before adding it to the base offset. size is greater than or equal to zero.

The expression yields the number of bits the new offset is displaced with respect to the base offset.

Example:

offset 1 = 0+(0:0:8 << 5)
offset 2 = 1+(1:16:8 << 6)