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.?

Jim Tonti (view profile)

on 11 Apr 2019
Latest activity Commented on by Jim Tonti

Jim Tonti (view profile)

on 22 Apr 2019
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}
I'm really hoping something like this already exists...

Star Strider

Star Strider (view profile)

on 11 Apr 2019
The whos function is probably as close as you can currently get to what you want.

Stephen Cobeldick (view profile)

on 11 Apr 2019
Edited by Stephen Cobeldick

Stephen Cobeldick (view profile)

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

James Tursa (view profile)

on 11 Apr 2019
Edited by James Tursa

James Tursa (view profile)

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?

Walter Roberson

Walter Roberson (view profile)

on 11 Apr 2019
computer() with three outputs outputs the Endian information. Which will be L for all x86 and x64 architectures, which is the only thing that has been supported since R2010a.
Jim Tonti

on 22 Apr 2019