Re: proto.h extension (unit strings)

[Guy Harris <guy () alum mit edu>]

On Dec 11, 2016, at 11:18 PM, Michal Labedzki <michal.labedzki () tieto com> wrote:

> Good idea. 
> I have similar problem with Bluetooth protocols. There is a lot of something like that:
> "Latency = N * 0.625 ms (1 Baseband slot)"

I.e., the value of the field is the number of baseband slots, and the latency, in milliseconds, is the number of 
baseband slots times .625?

> So I want to display [ms] instead of [slot] (or maybe both? [new use case]). What should I do in that case (N * 
> 0.625)? 
> 1. use own BASE_CUSTOM (dissector files)
> 2. public-predefined base custom function 
> 3. combine it with "BASE_UNIT" (unit_name_string_get_value in base custom function) or BASE_UNIT | BASE_CUSTOM?

Perhaps we could have a structure that contains 1) a set of unit strings and 2) a scale factor, and:

        if the scale factor is 0.0, there's no scaling;

        if the unit string pointers are NULL, there's no unit;

        otherwise, there's both scaling and a unit.

As for "or maybe both?", perhaps it'd be displayed as

        Latency: 0.625 ms (1)

although, for that, we might want to allow units for both the scaled and the unscaled value, to display it as

        Latency: 0.625 ms (1 baseband slot)

Should we have display-filter operators that work on both the raw value and the unscaled value, so that you could, for 
example, do

        ...latency == .625

or

        ...latency %= 1

(or whatever we choose for the two comparison operators).

> I think there should be abbrev-form of unit in "struct unit_name_string" (second, seconds, s) and provide user option 
> to choose between full-form and abbrev.

That might make sense.
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