java-topology/defects/fbneo-0001/test/test_burn_drv_get_index.cpp

// Unit test for fbneo-0001: BurnDrvGetIndex O(N) linear scan -> O(1) hash lookup.
// Models the defect: with 5000+ game drivers, every call to BurnDrvGetIndex
// (game load, state load, Kaillera/netplay) scanned the full driver array.
// Fix: build std::unordered_map<string, INT32> at BurnLibInit time, O(1) lookup.

#include <cassert>
#include <cstdio>
#include <chrono>
#include <string>
#include <vector>
#include <unordered_map>
#include <cstring>

// Minimal driver struct matching FBNeo's BurnDriver
struct BurnDriver {
    const char* szShortName;
};

// Original: O(N) linear scan
static int drv_get_index_original(const std::vector<BurnDriver*>& pDriver,
                                  const char* szName)
{
    if (!szName) return -1;
    for (int i = 0; i < (int)pDriver.size(); i++) {
        if (strcmp(szName, pDriver[i]->szShortName) == 0)
            return i;
    }
    return -1;
}

// Patched: O(1) hash lookup
struct PatchedIndex {
    std::unordered_map<std::string, int> map;

    void build(const std::vector<BurnDriver*>& pDriver) {
        map.clear();
        map.reserve(pDriver.size());
        for (int i = 0; i < (int)pDriver.size(); i++)
            map[pDriver[i]->szShortName] = i;
    }

    int get(const char* szName) const {
        if (!szName) return -1;
        auto it = map.find(szName);
        return (it != map.end()) ? it->second : -1;
    }
};

int main()
{
    // Build driver pool modeling FBNeo's ~5000 game drivers
    const int N_DRIVERS = 5000;
    std::vector<std::string> names;
    names.reserve(N_DRIVERS);
    for (int i = 0; i < N_DRIVERS; i++)
        names.push_back("drv_" + std::to_string(i));

    std::vector<BurnDriver> drivers(N_DRIVERS);
    std::vector<BurnDriver*> pDriver(N_DRIVERS);
    for (int i = 0; i < N_DRIVERS; i++) {
        drivers[i].szShortName = names[i].c_str();
        pDriver[i] = &drivers[i];
    }

    PatchedIndex idx;
    idx.build(pDriver);

    // Test 1: found at index 0 (best case original, same patched)
    {
        int orig = drv_get_index_original(pDriver, "drv_0");
        int patched = idx.get("drv_0");
        assert(orig == 0);
        assert(patched == 0);
        printf("PASS: lookup first driver\n");
    }

    // Test 2: found at last index (worst case original)
    {
        int orig = drv_get_index_original(pDriver, "drv_4999");
        int patched = idx.get("drv_4999");
        assert(orig == 4999);
        assert(patched == 4999);
        printf("PASS: lookup last driver\n");
    }

    // Test 3: not found returns -1
    {
        int orig = drv_get_index_original(pDriver, "no_such_game");
        int patched = idx.get("no_such_game");
        assert(orig == -1);
        assert(patched == -1);
        printf("PASS: missing driver returns -1\n");
    }

    // Test 4: null returns -1
    {
        int orig = drv_get_index_original(pDriver, nullptr);
        int patched = idx.get(nullptr);
        assert(orig == -1);
        assert(patched == -1);
        printf("PASS: null name returns -1\n");
    }

    // Test 5: correctness across all drivers
    {
        for (int i = 0; i < N_DRIVERS; i += 100) {
            assert(drv_get_index_original(pDriver, names[i].c_str()) == i);
            assert(idx.get(names[i].c_str()) == i);
        }
        printf("PASS: correctness across all %d drivers\n", N_DRIVERS);
    }

    // Test 6: performance -- lookup all N drivers once (covers entire range, no elision)
    {
        volatile int sink = 0;

        auto t0 = std::chrono::high_resolution_clock::now();
        for (int i = 0; i < N_DRIVERS; i++)
            sink += drv_get_index_original(pDriver, names[i].c_str());
        auto t1 = std::chrono::high_resolution_clock::now();
        for (int i = 0; i < N_DRIVERS; i++)
            sink += idx.get(names[i].c_str());
        auto t2 = std::chrono::high_resolution_clock::now();
        (void)sink;

        double orig_us = std::chrono::duration_cast<std::chrono::microseconds>(t1 - t0).count();
        double patch_us = std::chrono::duration_cast<std::chrono::microseconds>(t2 - t1).count();
        double ratio = orig_us / (patch_us > 0.0 ? patch_us : 1.0);

        printf("PASS: performance N=%d all-driver scan: original=%.0fus patched=%.0fus ratio=%.1fx\n",
               N_DRIVERS, orig_us, patch_us, ratio);
        // Scanning all N=5000 drivers takes O(N^2/2) comparisons vs O(N) hash lookups.
        // Even with vectorization the ratio must exceed 5x at N=5000.
        assert(ratio > 5.0);
    }

    printf("ALL TESTS PASSED\n");
    return 0;
}