Allow to describe bitfields in a struct template

[xairy]

Not sure how the syntax should look like.
Maybe something like this:

my_struct {
  field_1  const[1, int8] : 4
  field_2  int8 : 4
  field_3  int16 : 3
  field_4  int16[0:20] : 13
}

[dvyukov]

Please also post here some examples of where it is necessary. E.g. do we need to support consts, flags? Something else?

[xairy]

A couple of examples:

ipv4 header:
http://lxr.free-electrons.com/source/include/uapi/linux/ip.h#L85
https://en.wikipedia.org/wiki/IPv4#Header

ipv6 header:
http://lxr.free-electrons.com/source/include/uapi/linux/ipv6.h#L114
https://en.wikipedia.org/wiki/IPv6_packet#Fixed_header

[xairy]

We probably need to support const, flags and general integers (int8, int16, ...).

[xairy]

Proposed syntax:

my_struct {
  field_1  const[1, int8:4]
  field_2  int8:4
  field_3  len[parent, int16:3]
  field_4  int16:13[0:20]
}