MATLAB: Fi.sum increases bitlength although fimath is set to KeepMSB

fi.sumfixed-pointFixed-Point Designersum

Hi there,
I was wondering why the sum function increases the length of my fixed point variable.
Here is a little example:
fimath('SumMode','KeepMSB')
x = fi(1:100,true,8,0)
.
.
.
y = sum(x)
y = 5050
            DataTypeMode: Fixed-point: binary point scaling
              Signedness: Signed
              WordLength: 15
          FractionLength: 0
I actually expected y to be 39, which is the decimal representation of 00100111 (the first 8 bit of y). It seams that the sum function just works with FullPrecision anyways?! Am I doing something wrong here?
Any help is highly appreciated.
Regards,
Len

Best Answer

You did not specify SumWordLength in your fimath() object.
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