SHAMapNodeID.cpp

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#include <ripple/beast/core/LexicalCast.h>
#include <ripple/crypto/csprng.h>
#include <ripple/protocol/Serializer.h>
#include <ripple/shamap/SHAMap.h>
#include <ripple/shamap/SHAMapNodeID.h>
#include <cassert>
 
namespace ripple {
 
static uint256 const&
depthMask(unsigned int depth)
{
    enum { mask_size = 65 };
 
    struct masks_t
    {
        uint256 entry[mask_size];
 
        masks_t()
        {
            uint256 selector;
            for (int i = 0; i < mask_size - 1; i += 2)
            {
                entry[i] = selector;
                *(selector.begin() + (i / 2)) = 0xF0;
                entry[i + 1] = selector;
                *(selector.begin() + (i / 2)) = 0xFF;
            }
            entry[mask_size - 1] = selector;
        }
    };
 
    static masks_t const masks;
    return masks.entry[depth];
}
 
// canonicalize the hash to a node ID for this depth
SHAMapNodeID::SHAMapNodeID(unsigned int depth, uint256 const& hash)
    : id_(hash), depth_(depth)
{
    assert(depth <= SHAMap::leafDepth);
    assert(id_ == (id_ & depthMask(depth)));
}
 
std::string
SHAMapNodeID::getRawString() const
{
    Serializer s(33);
    s.addBitString(id_);
    s.add8(depth_);
    return s.getString();
}
 
SHAMapNodeID
SHAMapNodeID::getChildNodeID(unsigned int m) const
{
    assert(m < SHAMap::branchFactor);
 
    // A SHAMap has exactly 65 levels, so nodes must not exceed that
    // depth; if they do, this breaks the invariant of never allowing
    // the construction of a SHAMapNodeID at an invalid depth. We assert
    // to catch this in debug builds.
    //
    // We throw (but never assert) if the node is at level 64, since
    // entries at that depth are leaf nodes and have no children and even
    // constructing a child node from them would break the above invariant.
    assert(depth_ <= SHAMap::leafDepth);
 
    if (depth_ >= SHAMap::leafDepth)
        Throw<std::logic_error>(
            "Request for child node ID of " + to_string(*this));
 
    if (id_ != (id_ & depthMask(depth_)))
        Throw<std::logic_error>("Incorrect mask for " + to_string(*this));
 
    SHAMapNodeID node{depth_ + 1, id_};
    node.id_.begin()[depth_ / 2] |= (depth_ & 1) ? m : (m << 4);
    return node;
}
 
[[nodiscard]] std::optional<SHAMapNodeID>
deserializeSHAMapNodeID(void const* data, std::size_t size)
{
    std::optional<SHAMapNodeID> ret;
 
    if (size == 33)
    {
        unsigned int depth = *(static_cast<unsigned char const*>(data) + 32);
        if (depth <= SHAMap::leafDepth)
        {
            auto const id = uint256::fromVoid(data);
 
            if (id == (id & depthMask(depth)))
                ret.emplace(depth, id);
        }
    }
 
    return ret;
}
 
[[nodiscard]] unsigned int
selectBranch(SHAMapNodeID const& id, uint256 const& hash)
{
    auto const depth = id.getDepth();
    auto branch = static_cast<unsigned int>(*(hash.begin() + (depth / 2)));
 
    if (depth & 1)
        branch &= 0xf;
    else
        branch >>= 4;
 
    assert(branch < SHAMap::branchFactor);
    return branch;
}
 
SHAMapNodeID
SHAMapNodeID::createID(int depth, uint256 const& key)
{
    assert((depth >= 0) && (depth < 65));
    return SHAMapNodeID(depth, key & depthMask(depth));
}
 
}  // namespace ripple