Typecast a hex string to single

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Michael
Michael on 17 Aug 2022
Commented: Michael on 19 Aug 2022
I have strings of hex values that I need to typecast to single precision values. I don't actually care about the actual single precision value, I am just trying to package the binary into a single datatype for transmission.
I want something like
MyHexString = '7f8e2d38';
out = typecast(MyHexString,'single'); %This doesn't work because typecast needs number
But the typecast.m function requires a numeric value. All I want to do is to produce the single precision number equivalent of the binary data held in my hex string.
FYI: I was using
out = typecast(uint32(hex2dec(MyHexString)),'single');
This worked most of the time but is occasionally produced incorrect results because the hex2dec function produces a double and there is some loss on the subsequent uint32 cast. At least that's what I think is wrong.
How to I package hex into a single datatype?
  2 Comments
James Tursa
James Tursa on 18 Aug 2022
Edited: James Tursa on 18 Aug 2022
"... occasionally produced incorrect results ..."
Can you post some specific examples where this happens? How can there be a loss converting to uint32?

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Accepted Answer

Jan
Jan on 18 Aug 2022
Edited: Jan on 18 Aug 2022
str = '7f8e2d38';
vec = uint8(sscanf(str, '%2x'));
num = typecast(vec, 'single')
num = single 4.1379e-05
num = typecast(flip(vec), 'single') % Maybe MSB?
num = single NaN
NaN due to initial 7f
  13 Comments
Michael
Michael on 19 Aug 2022
Yes. That's what I was originally doing i.e. transmitting the raw binary. I believe the main issues I was having is that I was converting the double to a hex and then splitting up that hex. When one part of the resulting split hex string would result in a NaN value, using () +1i() in matlab would then force the other part of the number to be NaN as well. I got around that by using complext(real, imag). The code I posted above that splits the digits rather than the hex seems to do what I need related to transmitting time values. I believe that the transmission of the raw binary would work as well. Thanks for all your help!

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