nft.h

#pragma once
 
#include <xrpl/basics/base_uint.h>
#include <xrpl/basics/tagged_integer.h>
#include <xrpl/protocol/AccountID.h>
 
#include <boost/endian/conversion.hpp>
 
#include <cstdint>
#include <cstring>
 
namespace xrpl::nft {
 
// Separate taxons from regular integers.
struct TaxonTag
{
};
using Taxon = TaggedInteger<std::uint32_t, TaxonTag>;
 
inline Taxon
toTaxon(std::uint32_t i)
{
    return static_cast<Taxon>(i);
}
 
inline std::uint32_t
toUInt32(Taxon t)
{
    return static_cast<std::uint32_t>(t);
}
 
constexpr std::uint16_t const kFlagBurnable = 0x0001;
constexpr std::uint16_t const kFlagOnlyXrp = 0x0002;
constexpr std::uint16_t const kFlagCreateTrustLines = 0x0004;
constexpr std::uint16_t const kFlagTransferable = 0x0008;
constexpr std::uint16_t const kFlagMutable = 0x0010;
 
inline std::uint16_t
getFlags(UInt256 const& id)
{
    std::uint16_t flags = 0;
    memcpy(&flags, id.begin(), 2);
    return boost::endian::big_to_native(flags);
}
 
inline std::uint16_t
getTransferFee(UInt256 const& id)
{
    std::uint16_t fee = 0;
    memcpy(&fee, id.begin() + 2, 2);
    return boost::endian::big_to_native(fee);
}
 
inline std::uint32_t
getSequence(UInt256 const& id)
{
    std::uint32_t seq = 0;
    memcpy(&seq, id.begin() + 28, 4);
    return boost::endian::big_to_native(seq);
}
 
inline Taxon
cipheredTaxon(std::uint32_t tokenSeq, Taxon taxon)
{
    // An issuer may issue several NFTs with the same taxon; to ensure that NFTs
    // are spread across multiple pages we lightly mix the taxon up by using the
    // sequence (which is not under the issuer's direct control) as the seed for
    // a simple linear congruential generator.
    //
    // From the Hull-Dobell theorem we know that f(x)=(m*x+c) mod n will yield a
    // permutation of [0, n) when n is a power of 2 if m is congruent to 1 mod 4
    // and c is odd.
    //
    // Here we use m = 384160001 and c = 2459. The modulo is implicit because we
    // use 2^32 for n and the arithmetic gives it to us for "free".
    //
    // Note that the scramble value we calculate is not cryptographically secure
    // but that's fine since all we're looking for is some dispersion.
    //
    // **IMPORTANT** Changing these numbers would be a breaking change requiring
    //               an amendment along with a way to distinguish token IDs that
    //               were generated with the old code.
    return taxon ^ toTaxon(((384160001 * tokenSeq) + 2459));
}
 
inline Taxon
getTaxon(UInt256 const& id)
{
    std::uint32_t taxon = 0;
    memcpy(&taxon, id.begin() + 24, 4);
    taxon = boost::endian::big_to_native(taxon);
 
    // The taxon cipher is just an XOR, so it is reversible by applying the
    // XOR a second time.
    return cipheredTaxon(getSequence(id), toTaxon(taxon));
}
 
inline AccountID
getIssuer(UInt256 const& id)
{
    return AccountID::fromVoid(id.data() + 4);
}
 
}  // namespace xrpl::nft