Bitshift cannot work on negative numbers

I checked information of function"bitshift" on https://ww2.mathworks.cn/help/matlab/ref/bitshift.html?lang=en and find it can work for negative values:

intout = bitshift(A,k)

• If k is negative and A is negative, then MATLAB shifts the bits to the right and inserts |k| 1-bits on the left.

but when I applied it, if failed and report as below:

bitshift(-6,1)

Error using bitshift

Double inputs must have integer values in

the range of ASSUMEDTYPE.

My version is 2019b, is it beacuse of version or something else？

By the way, is there any website that allow us to refer to functions in previous version?

Answer 1

[Sulaymon Eshkabilov]

You've overlooked to specify the integer data format type, e.g.:

bitshift(-6,1, 'int8')
bitshift(-6,-1, 'int8')      

Works perfectly ok.

[Yuxin Gao]

Thanks for your answer, but the number I wanna deal with are big and I am not sure how many bits they are, if there is any assumedtype for double?

[Sulaymon Eshkabilov]

Max you can get is 64bit that means, you need to specify:

bitshift(-67776,1, 'int64')

[Yuxin Gao]

It works, thank you!

[Sulaymon Eshkabilov]

Most welcome!

Answer 2

[William]

I believe this is happening for the following reason: The documentation states that "If A is a double array, and ASSUMEDTYPE is not specified, then MATLAB treats A as an unsigned 64-bit integer." What this means is that the function implicitly sets the ASSUMEDTYPE argument to 'uint64'. Since your value of -6 is signed, and is therefore not in the range of a 'uint64', the function issues the error message. This is according to the second rule: "If ASSUMEDTYPE is specified, then all elements in A must have integer values within the range of ASSUMEDTYPE."

You can fix this by specifying that the assumed type is a signed integer rather than an unsigned integer. For example, you can use bitshift(-6,1,'int64'). But I would agree with you that the documentation is unclear.

[Yuxin Gao]

bitshift(-6,1,'int64') exactly works ,thank you!