Get bits of number.

I have a 16 bit double I got from using wavread that I want to get the first 8 bits from.

As an example lets say I have 67. Inside my computer it must be represented as a series of bits, 0111001 in this case. So lets say that I just want to have the last for of them 1001.

How can this be done?

[Guillaume]

You do not have a 16 bit double, since the double type is a 64-bit floating point number. single is 32-bit FP, and I'm not aware of a common 16-bit FP type.

You may have a 16-bit integer (signed or unsigned?)

[Guillaume]

Also, 67 in binary is not 00111001:

>>dec2bin(67, 8)
ans = 0100011

[Raldi]

I probably meant 57. Also yeah they are double but I calculated that I only need 16 bits to represent all numbers in that range, all the rest are zeros.

Answer 1

[Guillaume]

Assuming you have a 16 bit integer, the simplest way to extract some bits from it is to use bitget:

n = hex2dec('AF75'); %for example, bit pattern is 1010 1111 0111 0101.

bitpattern = bitget(n, 1:8, 'uint16')

returns

bitpattern = 

     1     0     1     0     1     1     1     0

You can also use dec2bin but that involves string conversion so is going to be slower.

[Raldi]

I get

Error using bitget
Too many input arguments.

I have to remove 'uint16' from the arguments. Even if I do so though I get

Inputs must be non-negative integers.

I have vR2011b by the way.

[Guillaume]

I'm not sure when the type specifier was added to bitget, I think it's fairly recent.

On older versions of matlab, this should work:

n = hex2dec('AF75'); %for example, bit pattern is 1010 1111 0111 0101.

bitpattern = bitget(uint16(n), 1:8)

That is convert your number (of type double) to an unsigned integer type.