Please can somebody expain this code.

tic
M = 'FFFFFFFFFFFFFFFF'; 
MB=[];  
for i=1:16 
  Mi=M(i); 
  MBi=['0000',dec2bin(hex2dec(Mi))]; 
  MBi=MBi(end-3:end); 
  MBi=[str2num(MBi(1)),str2num(MBi(2)),str2num(MBi(3)),str2num(MBi(4))]; 
end 
M=MB

[Kevin Claytor]

Did you have a look at the docs:

hex2dec

dec2bin

str2num

matrix indexing

They pretty much explain it. If you still don't understand the whole thing, post back with what you do understand and where you're getting stuck. You might also find;

Decimal Number

Binary Number

Hexadecimal Number

helpful.

I'm disappointed that I can't add the the link markup into code segments. It would have been more fun that way.

Answer 1

[Ishaan]

Hello @Syed Bilal,

The code you shared appears to convert a 16-character hexadecimal string into its equivalent binary representation.

Refer to the following code with added comments and some improvements for better understanding.

tic  % Start a timer to measure the execution time of the code 

M = 'FFFFFFFFFFFFFFFF';  % Initialize a string representing a 16-character hexadecimal number 
MB = [];  % Initialize an empty array to store binary representations 

for i = 1:16  % Loop through each character in the hexadecimal string 
    Mi = M(i);  % Extract the i-th character from the hexadecimal string M 
    % Convert the hexadecimal character to a decimal number, then to a binary string 
    MBi = ['0000', dec2bin(hex2dec(Mi))];   
    % Ensure the binary string is 4 characters long by taking the last 4 characters 
    MBi = MBi(end-3:end);   
    % Convert each character in the binary string to a number and store in MBi 
    MBi = [str2double(MBi(1)), str2double(MBi(2)), str2double(MBi(3)), str2double(MBi(4))];   
    MB = [MB, MBi];  % Append the binary array to MB 
end 

M = MB  % Assign the final binary representation to M 

M = 1×64

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

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toc;  % End the timer and report the execution time 

Elapsed time is 0.131393 seconds.

I noticed 3 potential errors in the code you provided and made these changes.

1. The result at each intermediate step is not stored and is overridden. Added the line “MB = [MB, MBi];” at the end of the loop to that.
2. ‘str2num` is not recommended in this case as it is not suitable for converting single character strings to numbers. Instead, you should use “str2double” or directly convert the character to a number using “-'0'” which works well for character arrays representing digits.
3. “tic” was used without “toc”. “tic” marks the start of the timer and “toc” marks its end reporting/returning the time it took for the code to execute between the two. I added "toc" at the end of the code.

I hope that it is now clear what the code snippet you provided does.

[Walter Roberson]

dec2bin(hex2dec(Mi),4)

would make more sense then the string manipulation you are doing.

[Walter Roberson]

Instead of

MBi = [str2double(MBi(1)), str2double(MBi(2)), str2double(MBi(3)), str2double(MBi(4))]; 

you can use

MBi = MBi - '0';