Hi all,
while implementing the mspec for KNXnet/IP I stumbled into the first pit
regarding floating point numbers.
In the spec they claim to be normal IEEE 754 half precision floating point
numbers and therefore I thought a “float 16” would be ok.
However it turned out that they don’t use the formal half precision types. The
exponent is one bit less and the mantissa is one bit more.
So I think it would be great to change the float datatype to something like
float +4.11
If there’s a “+” it’s a signed floating point (Alternatively we could add a
“ufloat” type) … the main thing is that then comes the number of exponent bits
and after the dot the mantissa.
Right now I “solved” the problem like this:
['9' KnxDatapointF16
[reserved uint 8 '0x0']
[simple bit 'sign']
[simple int 4 'exponent']
[simple uint 11 'mantissa']
[virtual float 16 'val' '(sign ? -1 : 1) * (0.01 * mantissa) * (2 ^
exponent)']
]
Which is not that ideal …
What do you think?
The more I think of it, I think a: “float” and a “ufloat” is the better idea as
this continues the int / uint concept for integers.
Chris
