How To Calculate Merkle Root?

Question

I found this example:

---

Current merkle hash list: 32650049a0418e4380db0af81788635d8b65424d397170b8499cdc28c4d27006 30861db96905c8dc8b99398ca1cd5bd5b84ac3264a4e1b3e65afa1bcee7540c4

Current merkle hash list: d47780c084bad3830bcdaf6eace035e4c6cbf646d103795d22104fb105014ba3

---

I have tried to calculate the hash using PHP:

$tx1="32650049a0418e4380db0af81788635d8b65424d397170b8499cdc28c4d27006";
$tx2="30861db96905c8dc8b99398ca1cd5bd5b84ac3264a4e1b3e65afa1bcee7540c4";
$v=hash('sha256', hash('sha256',$tx1.$tx2) );

But I got:
2b5f377b4adab64f489a2f73605ffb448b8add5b708d218729f9dfc58f1f5fe2

What is wrong?

Answer 1

This is the correct way to double hash two tx's. First you need to convert them into little endian, and then convert into raw binary data before hashing.

<?php

function le_raw ($str) {
    return pack("H*", join("", array_reverse(str_split($str, 2))) );
    // return map { pack "H*", join "", reverse /(..)/g } @_;
}
function be_hex ($raw) {
    return join("", array_reverse(str_split( unpack("H*", $raw)[1], 2)));
    // return map { join "", reverse unpack("H*", $_) =~ /(..)/g } @_;
}

$tx1 = le_raw("32650049a0418e4380db0af81788635d8b65424d397170b8499cdc28c4d27006");
$tx2 = le_raw("30861db96905c8dc8b99398ca1cd5bd5b84ac3264a4e1b3e65afa1bcee7540c4");
$v = hash('sha256', hash('sha256', $tx1.$tx2, true), true );

echo be_hex($v), "\n";

output

d47780c084bad3830bcdaf6eace035e4c6cbf646d103795d22104fb105014ba3