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hex2num can't recover value from the hex by num2hex

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david wang
david wang on 19 Dec 2019
Commented: Walter Roberson on 21 Dec 2019
my matlab script
num2hex(single(-1.7783722e-1))
ans =
'be361af6'
and
hex2num('be361af6')
ans =
-5.146794990196213e-09
why I can not recover the original value ?

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Accepted Answer

Rik
Rik on 19 Dec 2019
As the documentation explains, hex2num assumes the hex is a representation of a double, while num2hex also supports the single data type. That means that despite the names, these two functions are not the exact mirror of each other.
It looks like you will have to implement hex2num yourself if you want to have a single as an output.

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david wang
david wang on 21 Dec 2019
Rik: thanks for the answer and explanation !

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More Answers (1)

James Tursa
James Tursa on 19 Dec 2019
Try
typecast(uint32(hex2dec('be361af6')),'single')

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Walter Roberson
Walter Roberson on 21 Dec 2019
This will work for the case of single, but hex2dec() cannot substitute for hex2num() for the case where the input is representing double: for a lot of the important range, the decimal results produced by hex2num() would be outside what can be represented as double precision.
Instead of hex2dec, the form that is more generally usable is
sscanf(HEXSTRING, '%lx')
which gives back a uint64 that you can then typecast.
typecast(uint32(sscanf('be361af6', '%lx')),'single')
typecast(sscanf('400921fb54442d18', '%lx'), 'double')

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