CODEWITHSUNDEEP
phpintegerhexincrement
FEL
FEL

Reputation: 39

Increment hex value (little endian?) in PHP

In an incoming UDP packet I have the hex value b70500. This is actually a sequence number (1463). I need to increment this value before sending it back to the server in the same format (b80500).

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How can I, in PHP, increment the value by one?

Using the code suggested here I was able to convert the hex value to an integer and increment it by one:

$original_hex = 'b70500';                                        // 1463
$original_int = unpack("H*", strrev(pack("H*", $original_hex))); // 0005b7
$incremented_int = hexdec($original_int[1]) + 1;                 // 1464
$incremented_hex = ?                                             // Expected result: b80500

... But I have no idea how to convert it back into hex. Perhaps there is a more efficient method?

Upvotes: 2

Views: 2219

Answers (2)

FEL
FEL

Reputation: 39

It's not pretty and I bet there are more efficient ways of doing this, but it works:

function increment_hex($hex) {
  $original_hex = $hex;
  $original_int = unpack("H*", strrev(pack("H*", $original_hex)));
  $incremented_int = hexdec($original_int[1]) + 1;
  $incremented_hex = dechex($incremented_int);

  $padded_hex = str_pad($incremented_hex, 6, '0', STR_PAD_LEFT);
  $reversed_hex = unpack("H*", strrev(pack("H*", $padded_hex)));

  return $reversed_hex[1];
}

echo "result: " . increment_hex('b70500') . "\n";

result: b80500

Upvotes: 1

Sverri M. Olsen
Sverri M. Olsen

Reputation: 13283

hexdec() and dechex(). You do not have to unpack the value.

$incremented = dechex(hexdec('b70500') + 1);

Upvotes: 2

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