user56046: I remember some where was table and python scrypt for do this , when reinstall my debian i was lose this script.
Example we hv uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff"); 
what is = 0x1d00ffff

user48884: The formula for the conversion can be found on the bitcoin wiki.
Essentially, the first byte indicates the number of trailing 0 bytes (minus 3 for some reason). The remaining 3 bytes are the next 3 bytes of the target.
So 0x1d00fffff has 0x00ffff followed by 0x1d - 3 = 26 trailing 0 bytes with the whole thing padded out to 32 bytes. So the final result is 0x00000000ffff00000000000000000000000000000000000000000000000000000.

56046: <p>I remember some where was table and python scrypt for do this , when reinstall my debian i was lose this script.</p>

<p>Example we hv uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff"); 
what is = 0x1d00ffff</p>
 48884: <p>The formula for the conversion can be found on <a href="https://en.bitcoin.it/wiki/Difficulty" rel="nofollow noreferrer">the bitcoin wiki</a>.</p>

<p>Essentially, the first byte indicates the number of trailing 0 bytes (minus 3 for some reason). The remaining 3 bytes are the next 3 bytes of the target.</p>

<p>So <code>0x1d00fffff</code> has <code>0x00ffff</code> followed by <code>0x1d - 3 = 26</code> trailing 0 bytes with the whole thing padded out to 32 bytes. So the final result is <code>0x00000000ffff00000000000000000000000000000000000000000000000000000</code>.</p>
