Re: [PATCH net-next v4 3/5] ipv4: igmp: encode multicast exponential fields

Ido Schimmel
2026-04-13T08:47:22Z

On Sun, Apr 12, 2026 at 11:10:45AM +0000, Ujjal Roy wrote:
> In IGMP, MRC and QQIC fields are not correctly encoded
> when generating query packets. Since the receiver of the
> query interprets these fields using the IGMPv3 floating-
> point decoding logic, any value that exceeds the linear
> threshold is incorrectly parsed as an exponential value,
> leading to an incorrect interval calculation.
>
> Encode and assign the corresponding protocol fields during
> query generation. Introduce the logic to dynamically
> calculate the exponent and mantissa using bit-scan (fls).
> This ensures MRC and QQIC fields (8-bit) are properly
> encoded when transmitting query packets with intervals
> that exceed their respective linear threshold value of
> 128 (for MRT/QQI).
>
> RFC3376: for both MRC and QQIC, values >= 128 represent
> the same floating-point encoding as follows:
> 0 1 2 3 4 5 6 7
> +-+-+-+-+-+-+-+-+
> |1| exp | mant |
> +-+-+-+-+-+-+-+-+
>
> Signed-off-by: Ujjal Roy <royujjal@gmail.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>