Wireshark · Wireshark-dev: [Wireshark-dev] "Scaled" integer fields in a protocol, can use proto_tree_add_item??

[John Jamulla <jjamulla@xxxxxxxxx>]

Hi,

In my protocol I have many fields (simple integers) that are scaled. For the most part in the GUI display I want to print
the "human readable" numbers. So, Say I have a field that represents ft of altitude, I want to print "XX ft", not the scaled number in the actual packet.
I need to take the value actually in the packet and multiple it by say .5 (or any number) to
get the real number of feet of altitude (so that it ranges from .5 ft to XX ft. in .5 ft steps.)
I know how to get it from a bitmask/bitfield using standard wireshark functions, but I still need to scale the number
many times.

I don't want to do anything complicated to decode this type of field, and it seems like it should be easier than what I'm doing.
I just want something like what's normally done, something like this:
proto_tree_add_item(asicp_tree, hf_asicp_mymsg_alt, tvb,  offset, 4, TRUE);

BUT - I want some way to have it scale what it gets from the packet (since it's automatically getting and using the number from the packet data) by a value/number I supply.
Is there such a function in wireshark? If not is there another way I'm supposed to be doing this?
Can anyone point me to a good example?

Here's an example of what I've been doing (a little more involved than above example but same thing):
                  madd_atten = tvb_get_letohs (tvb, offset);
                  madd_atten = madd_atten & MADD_ATTEN_MASK_405MSG;
                  madd_attenReal = madd_atten * 0.25;    
                  g_snprintf(maddAttenString, MAX_STRING_BUFFER,
                 "Generator (0-%d) [%3d]: MADD ATTEN = %f (0.25 dB lsb)",
                 GENERATORS_PER_405_MSG-1, i, madd_attenReal);
                  proto_tree_add_string_format(asicp_tree, hf_asicp_405_maddattenstring,
                           tvb,  offset, 2, maddAttenString,
                     "%s", maddAttenString);

Any help is appreciated.
Thanks,
    John Jamulla