dec2bin is not precise with 64 bits numbers

Hi, I was trying to apply a left circular shift to a 64 bits number, when I notice that dec2bin does'nt work correctly, Have you any idea how to fix it? for example:

     dec2bin(double(9223372036855037954))

     ans =

         1000000000000000000000000000000000000000000001000000000000000000
But the right anwser that I expect is:      
         1000000000000000000000000000000000000000000001000000000000000010

Answer 1

[Thomas]

For dec2bin to work correctly it should be nonnegative integer smaller than 2^52

It is mentioned int he documentation: http://www.mathworks.com/help/techdoc/ref/dec2bin.html

Answer 2

[Walter Roberson]

double(9223372036855037954) is not a 64 bit number: it is an IEEE 754 Double Precision Floating Point number.

Please see http://www.mathworks.com/matlabcentral/answers/13142-dec2bin and in particular the last comment I made (about 64 bit constants.)

Answer 3

[suzi freunden]

thanks for the answers, I have another question: is there a function doing a correct bitshift for unsigned integer bigger than 2^52? I'm using R2009b

[Jan]

BITSHIFT works correctly with UINT64 in 2009a. Only reading the value fails.

Answer 4

[John D'Errico]

So use a tool (vpi, found on the FEX) designed to handle large numbers.

>> vpi2bin(vpi('9223372036855037954'))
ans =
1000000000000000000000000000000000000000000001000000000000000010

Or for that matter, if you like bigger numbers...

>> vpi2bin(vpi('92233720368556346354667564688567567858565037954'))
ans =
1000000100111111001110010111100011111000101000010100010011111110011000001110001001010001100001110111110110100110000010110001111110011111100101011111110000010

[suzi freunden]

thanks a lot for your help, but I get this error when using vpi package:

D = vpi(2)^75 - 1;

??? Undefined function or method 'vpi' for input arguments of type 'double'.

vpi2bin(vpi(9223372036855037954))

??? Undefined function or method 'vpi' for input arguments of type 'double'.

[Walter Roberson]

vpi is a MATLAB File Exchange (FEX) contribution. You need to download it and install it on your machine.

[suzi freunden]

To use the vpi (Variable Precision Integer) arithmetic tools, you will need to have the top level directory (VariablePrecisionIntegers) on your MATLAB search path.\

I just download it and change MATLAB search path there is no .exe or something like