merkleroot.php

#!/usr/bin/php
<?php

// Swap Endian function
function swapendian($data) {
    return implode('', array_reverse(str_split($data, 2)));
}

// Merkle Root Function
function merklerootbinary($txids) {

    // Stop recursion if there is only one hash value left, because that's the merkle root.
    if (count($txids) == 1) {
        $merkleroot = $txids[0];
        return $merkleroot;
    }

    else {

        // Create the new array of hashes
        while (count($txids) > 0) {

            if (count($txids) >= 2) {
                // Get first two
                $pair_first = $txids[0];
                $pair_second = $txids[1];

                // Hash them (double SHA256)
                $pair = $pair_first.$pair_second;
                $pairhashes[] = hash('sha256', hash('sha256', $pair, true), true);

                // Remove those two from the array
                unset($txids[0]);
                unset($txids[1]);

                // Re-set the indexes (the above just nullifies the values) and make a new array without the original first two slots.
                $txids = array_values($txids);
            }

            if (count($txids) == 1) {
                // Get the first one twice
                $pair_first = $txids[0];
                $pair_second = $txids[0];

                // Hash it with itself (double SHA256)
                $pair = $pair_first.$pair_second;
                $pairhashes[] = hash('sha256', hash('sha256', $pair, true), true);

                // Remove it from the array
                unset($txids[0]);

                // Re-set the indexes (the above just nullifies the values) and make a new array without the original first two slots.
                $txids = array_values($txids);
            }

        }

        // Recursion bit. Re-apply this function to the new array of hashes we've just created.
        return merklerootbinary($pairhashes);

    }

}

function merkleroot($txids) {

    // Convert txids in to big endian (BE), because that's the format they need to be in to get the merkle root.
    foreach ($txids as $txid) {
        $txidsBE[] = swapendian($txid);
    }

    // Now convert each of these txids in to binary, because the hash function wants the binary value, not the hex.
    foreach ($txidsBE as $txidBE) {
        $txidsBEbinary[] = hex2bin($txidBE);
    }

    // Work out the merkle root (in binary) using that lovely recursive function above.
    $merkleroot = merklerootbinary($txidsBEbinary);

    // Convert the merkle root in to hexadecimal and little-endian, because that's how it's stored in the block header.
    $merkleroot = swapendian(bin2hex($merkleroot));

    // Return it :)
    return $merkleroot;

}


// Get lines from STDIN
$lines = file('php://stdin');

// Clean up input (remove whitespace and ")
$txids = [];
foreach ($lines as $line) {
    $txids[] = str_replace('"', '', trim($line));
}

// Work out the Merkle Root
$merkleroot = merkleroot($txids);

// Print Result
echo $merkleroot."\n";