How to Perform Bit-Level Operations on Binary Strings in PHP Using bindec() and substr()

When working with binary strings in PHP, it's common to encounter situations where you need to extract or modify certain bits. The bindec() function converts a binary string to a decimal integer, while the substr() function allows us to extract a part of a string. By combining both functions, bit-level operations on binary strings can be easily achieved.

Overview of bindec() and substr()

• bindec(string $binary_string): int
  Converts a binary string to a decimal integer. For example, bindec('101') returns 5.

• substr(string $string, int $start, int $length = null): string
  Extracts a substring from a string. For example, substr('101101', 2, 3) returns '110'.

Example: Extract Specific Bits from a Binary String and Convert to Decimal

Suppose you have a binary string and you want to extract 4 bits starting from the 3rd position and then convert them to decimal.

<?php
$binaryString = "1101011011"; // Original binary string
<p>// Use substr to extract 4 bits starting from index 2 (indexing starts at 0)<br>
$subBinary = substr($binaryString, 2, 4); // "0101"</p>
<p>// Use bindec to convert the extracted binary string to decimal<br>
$decimalValue = bindec($subBinary);</p>
<p>echo "Binary substring: " . $subBinary . "\n";      // Output: 0101<br>
echo "Corresponding decimal value: " . $decimalValue . "\n"; // Output: 5<br>
?><br>

Explanation of Example

• substr($binaryString, 2, 4): Extracts 4 bits starting from the 3rd character of the original string (indexing starts at 0), resulting in "0101".

• bindec("0101"): Converts "0101" to decimal 5.

Advanced: Modify a Specific Bit in a Binary String

In addition to extraction, you can also modify a specific bit in a binary string:

<?php
$binaryString = "1101011011";
<p>// Set the 5th bit (index 4) to 1<br>
$pos = 4;<br>
$newBit = '1';</p>
<p>// Modify the string<br>
$binaryString = substr_replace($binaryString, $newBit, $pos, 1);</p>
<p>echo "Modified binary string: " . $binaryString . "\n";<br>
?><br>

Summary

By combining substr() for extracting parts of a string and bindec() for conversion, you can easily perform bit-level extraction and conversion on binary strings. With additional string manipulation functions, even more complex binary data processing can be achieved.