TigerTree.cc

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#include "TigerTree.hh"
 
#include "tiger.hh"
#include "Math.hh"
#include "MemBuffer.hh"
#include "ScopedAssign.hh"
 
#include <cassert>
#include <map>
#include <span>
 
namespace openmsx {
 
struct TTCacheEntry
{
        struct Info {
                TigerHash hash;
                bool valid;
        };
        MemBuffer<Info> nodes;
        time_t time = -1;
        size_t numNodesValid;
};
// Typically contains 0 or 1 element, and only rarely 2 or more. But we need
// the address of existing elements to remain stable when new elements are
// inserted. So still use std::map instead of std::vector.
static std::map<std::pair<size_t, std::string>, TTCacheEntry> ttCache;
 
[[nodiscard]] static constexpr size_t calcNumNodes(size_t dataSize)
{
        auto numBlocks = (dataSize + TigerTree::BLOCK_SIZE - 1) / TigerTree::BLOCK_SIZE;
        return (numBlocks == 0) ? 1 : 2 * numBlocks - 1;
}
 
[[nodiscard]] static TTCacheEntry& getCacheEntry(
        TTData& data, size_t dataSize, const std::string& name)
{
        auto& result = ttCache[std::pair(dataSize, name)];
        if (!data.isCacheStillValid(result.time)) { // note: has side effect
                size_t numNodes = calcNumNodes(dataSize);
                result.nodes.resize(numNodes);
                for (auto& i : result.nodes) i.valid = false; // all invalid
                result.numNodesValid = 0;
        }
        return result;
}
 
TigerTree::TigerTree(TTData& data_, size_t dataSize_, const std::string& name)
        : data(data_)
        , dataSize(dataSize_)
        , entry(getCacheEntry(data, dataSize, name))
{
}
 
const TigerHash& TigerTree::calcHash(const std::function<void(size_t, size_t)>& progressCallback)
{
        return calcHash(getTop(), progressCallback);
}
 
void TigerTree::notifyChange(size_t offset, size_t len, time_t time)
{
        entry.time = time;
 
        assert((offset + len) <= dataSize);
        if (len == 0) return;
 
        if (entry.nodes[getTop().n].valid) {
                entry.nodes[getTop().n].valid = false; // set sentinel
                entry.numNodesValid--;
        }
        auto first = offset / BLOCK_SIZE;
        auto last = (offset + len - 1) / BLOCK_SIZE;
        assert(first <= last); // requires len != 0
        do {
                auto node = getLeaf(first);
                while (entry.nodes[node.n].valid) {
                        entry.nodes[node.n].valid = false;
                        entry.numNodesValid--;
                        node = getParent(node);
                }
        } while (++first <= last);
}
 
const TigerHash& TigerTree::calcHash(Node node, const std::function<void(size_t, size_t)>& progressCallback)
{
        auto n = node.n;
        auto& nod = entry.nodes[n];
        if (!nod.valid) {
                if (n & 1) {
                        // interior node
                        auto left  = getLeftChild (node);
                        auto right = getRightChild(node);
                        const auto& h1 = calcHash(left, progressCallback);
                        const auto& h2 = calcHash(right, progressCallback);
                        tiger_int(h1, h2, nod.hash);
                } else {
                        // leaf node
                        size_t b = n * (BLOCK_SIZE / 2);
                        size_t l = dataSize - b;
 
                        if (l >= BLOCK_SIZE) {
                                auto* d = data.getData(b, BLOCK_SIZE);
                                tiger_leaf(std::span{d, BLOCK_SIZE}, nod.hash);
                        } else {
                                // partial last block
                                auto* d = data.getData(b, l);
                                auto sa = ScopedAssign(d[-1], uint8_t(0));
                                tiger(std::span{d - 1, l + 1}, nod.hash);
                        }
                }
                nod.valid = true;
                entry.numNodesValid++;
                if (progressCallback) {
                        progressCallback(entry.numNodesValid, entry.nodes.size());
                }
        }
        return nod.hash;
}
 
 
// The TigerTree::nodes member variable stores a linearized binary tree. The
// linearization is done like in this example:
//
//                   7              (level = 8)
//             ----/   \----        .
//           3              11      (level = 4)
//         /   \           /  \     .
//       1       5       9     |    (level = 2)
//      / \     / \     / \    |    .
//     0   2   4   6   8  10  12    (level = 1)
//
// All leaf nodes are given even node values (0, 2, 4, .., 12). Leaf nodes have
// level=1. At the next level (level=2) leaf nodes are pair-wise combined in
// internal nodes. So nodes 0 and 2 are combined in node 1, 4+6->5 and 8+10->9.
// Leaf-node 12 cannot be paired (there is no leaf-node 14), so there's no
// corresponding node at level=2. The next level is level=4 (level values
// double for each higher level). At level=4 node 3 is the combination of 1 and
// 5 and 9+12->11. Note that 11 is a combination of two nodes from a different
// (lower) level. And finally, node 7 at level=8 combines 3+11.
//
// The following methods navigate in this tree.
 
TigerTree::Node TigerTree::getTop() const
{
        auto n = Math::floodRight(entry.nodes.size() / 2);
        return {n, n + 1};
}
 
TigerTree::Node TigerTree::getLeaf(size_t block) const
{
        assert((2 * block) < entry.nodes.size());
        return {2 * block, 1};
}
 
TigerTree::Node TigerTree::getParent(Node node) const
{
        assert(node.n < entry.nodes.size());
        do {
                node.n = (node.n & ~(2 * node.l)) + node.l;
                node.l *= 2;
        } while (node.n >= entry.nodes.size());
        return node;
}
 
TigerTree::Node TigerTree::getLeftChild(Node node) const
{
        assert(node.n < entry.nodes.size());
        assert(node.l > 1);
        node.l /= 2;
        node.n -= node.l;
        return node;
}
 
TigerTree::Node TigerTree::getRightChild(Node node) const
{
        assert(node.n < entry.nodes.size());
        while (true) {
                assert(node.l > 1);
                node.l /= 2;
                auto r = node.n + node.l;
                if (r < entry.nodes.size()) return {r, node.l};
        }
}
 
} // namespace openmsx