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What function returns (as an integer) the number of bits in a data type or class, e.g. returns 16 for 'int16' or 'uint16' variables, 32 (or whatever) for 'float' types, etc.?

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Jim Tonti
Jim Tonti on 11 Apr 2019
Edited: Jim Tonti on 7 Jun 2021
The MATLAB function intmax() is close, but is only defined for integer types up to 32 bits. The function class() returns type variable type, but metainformation has to be inferred from documentation for the particular version of MATLAB after that.
Is there a function that returns the native bit size (i.e. the number of bits used for internal storage), or even more useful, all metadata about a given variable or class?
An extension to the function might return other metadata about the variable type, e.g. IEEE format, number of bits, signed/unsigned, etc.
Here's how it might work:
A = uint64(1234);
varinfo(A)
ans =
64
[nBits, meta] = varinfo(A)
nBits =
64
meta =
class = 'uint64'
nBits = 64
signed = 0
value = 1234
format = 'IEEE ...
nExp = 0
nMantissa = 64
max = {actual intmax for the type}
min = {actual minimum value > 0}
{and other useful metadata about the variable)
I'm really hoping something like this already exists...

Accepted Answer

Stephen
Stephen on 11 Apr 2019
Edited: Stephen on 11 Apr 2019
>> A = single(0);
>> S = whos('A');
>> S.class
ans = single
>> S.bytes*8
ans = 32
If you have non-scalar arrays to get the bits (or bytes) per element simply divide by the number of elements (does not work for empty arrays), or use cast:
B = cast(0,S.class)
S = whos('B');
S.bytes*8
S.class

More Answers (1)

James Tursa
James Tursa on 11 Apr 2019
Edited: James Tursa on 11 Apr 2019
I think everything that MATLAB runs on currently uses IEEE single and double floating point formats. And the signed integer formats are two's complement storage. Char is actually two bytes per value. Logical is one byte per value. Differences would be big or little endian. So you could easily write a function that gives all of this info, but most of the results would be the same across all platforms for a given class.
What would you use such a function for?
  3 Comments
Walter Roberson
Walter Roberson on 7 Jun 2021
Side note: in some recent releases, Apple M1 has been supported. It is a 64 bit ARM CPU.
Microsoft is working on a 64 bit ARM operating system, but at the moment it is quite unreliable, and their 32 bit ARM is more stable but not great.
... so the list of architectures supported these days has to include ARM

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