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    SubjectInsanely high baud rates
    Date
    [Resending to a wider audience]

    In trying to get the termios2 interface actually implemented in glibc,
    the question came up if we will ever care about baud rates in excess of
    4 Gbps, even in the relatively remote future.

    If this is something we care about *at all*, I would like to suggest
    that rather than defining yet another kernel interface, we steal some
    bits from the MSB of the speed fields, alternatively one of the c_cc
    bytes (all likearchitectures seem to have c_cc[18] free) or some field,
    if we can find them, in c_cflags, to indicate an exponent.

    With 5 bits from the top of the speed fields, the current values would
    be identical up to 248 Gbps, and values up to ~288 Pbps would be
    encodable ±2 ppb.

    In the short term, all we would have to do in the kernel would be
    erroring out on baud rates higher than 0x0fffffff (2^28-1 due to
    implicit one aliasing rhe first bit of a 5-bit exponent – less than 2^27
    are functionally denorms.) However, I'd like to put the glibc
    infrastructure for this now if this is something we may ever be
    interested in.

    Thoughts?
    --
    Sent from my Android device with K-9 Mail. Please excuse my brevity.

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