incorrect CRC computation

[Cédric Baudoin]

In RoHCv1.2.0, the CRC for compressed packets (UOR-*, UO-*....) is being computed over the entire 'uncompressed header' rather then following the guidelines provided in section5.9 (of RFC3095) for CRC coverage and computation. RFC3095 mentions that for CRC-3 & CRC-7 the uncompressed header should be divided in 'CRC-Static' and 'CRC-Dynamic' fields and the CRC should be computed. This is not followed in the RoHCv1.2.0 code.

[Julien BERNARD (j-bernard)]

Here is a patch for correct CRC computation for the main branch.
For the moment, the CRC-STATIC is always computed although it should be saved and computed only if a 'STATIC' field change.

[Didier Barvaux (didier-barvaux)]

Do not fix the problem on the 1.2.x branch as it will change the format of some ROHC packets. Compatibility between 1.2.x releases must be preserved. Update the "known problems" section in README to mention the bug. See http://bazaar.launchpad.net/~didier-barvaux/rohc/1.2.x/revision/109

[Didier Barvaux (didier-barvaux)]

Fixed in trunk for next 1.3.0 release. The CRC computation could be improved later by storing CRC-STATIC in the context. This would avoid CRC-STATIC re-computation for every packet. See http://bazaar.launchpad.net/~didier-barvaux/rohc/main/revision/122 for commit details.

Patch provided by Julien Bernard. Many thanks to him.