Convert IEEE754 to hex in PHP

Question

For the project, I need to read the information from MQTT. The payload is filled with protobuf information that needs to be converted.

For a specific value, I get 5.6904566139035E-28 as a float. Using http://www.exploringbinary.com/floating-point-converter/ I can convert this when I mark a single and hexadecimal hex value, then I get 12345678, the value I should have (I know what is sent).

But now I need to do this conversion to PHP. I do not know how to do this. After some reading, I realized that this is a floating point, but how to convert it, as it is done on this website.

Is there anyone who can help me?

Thank you so much!

Answer 1

With pretty cryptic packages and unpacking features, this can be done in single-line mode:

function rawSingleHex($num) { return strrev(unpack('h*', pack('f', $num))[1]); } 

This “packs” the number as its binary representation, then “unpacks” it into an array with one element: the binary representation in hexadecimal format. This format has the numbers in reverse order, so the function cancels this in the final result.

Call it by passing a floating point number:

 echo rawSingleHex(5.6904566139035E-28); 

Output:

12345678

No package / package

(this was my initial answer, but with the first option available, this is not a recommended way to continue)

The binary format is explained in the Wikipedia article on the single-precision floating point format .

Here is a PHP function that implements the described procedure:

 function rawSingleHex($num) { if ($num == 0) return '00000000'; // set sign bit, and add another, higher one, which will be stripped later $sign = $num < 0 ? 0x300 : 0x200; $significant = abs($num); $exponent = floor(log($significant, 2)); // get 24 most significant binary bits before the comma: $significant = round($significant / pow(2, $exponent-23)); // exponent has exponent-bias format: $exponent += 127; // format: 1 sign bit + 8 exponent bits + 23 significant bits, // without left-most "1" of significant $bin = substr(decbin($sign + $exponent), 1) . substr(decbin($significant), 1); // assert that result has correct number of bits: if (strlen($bin) !== 32) { return "unexpected error"; } // convert binary representation to hex, with exactly 8 digits return str_pad(dechex(bindec($bin)), 8, "0", STR_PAD_LEFT); } 

It outputs the same as in the first decision.