sots-engine/tests/app/test_alliance.cpp

// The alliance / shared-vision mask, pinned as a rule rather than as a table of observations.
//
// The corpus agrees with this rule on 72 of 80 player-records and predicts the other 8 (the
// zero masks of every save's earliest archived turn, which the load path wrote without a
// spine). That comparison lives in app_test_turn_record, where the stored bytes are. What is
// pinned HERE is the part the corpus cannot separate:
//
//   * the bit is the player's position in the vector, not its own index field. Every save in
//     the corpus has the two equal, so no comparison against stored bytes can tell them
//     apart -- only the instruction stream can, and this test holds the reading.
//   * the mask is an OR of the self bit with the alliance's member mask. In the corpus every
//     observed alliance mask already contains its member's own bit, so `self | AL` and `AL`
//     are indistinguishable there.
//   * the guard is on the alliance id, not on the member mask being non-zero. In the corpus
//     the two always agree, because a player with no alliance id also has a zero mask.
//
// Three cases that no save exercises, each held here so that a later save which does
// exercise one has something to disagree with.
#include <cstdio>

#include "app/alliance.h"
#include "mars/stream/shapes.h"

static int failures = 0;
#define CHECK_EQ(a, b)                                                          \
    do {                                                                        \
        const long long va = (long long)(a), vb = (long long)(b);               \
        if (va != vb) {                                                         \
            std::printf("FAIL %s:%d  %s == %s  (%lld != %lld)\n", __FILE__,     \
                        __LINE__, #a, #b, va, vb);                              \
            ++failures;                                                         \
        }                                                                       \
    } while (0)

using mars::stream::shapes::Player;
using mars::stream::shapes::PlayerEntry;

static Player MakePlayer(int plyrIdx, int alid, int al) {
    Player p;
    p.plyrIdx = plyrIdx;
    p.alliances.alid = alid;
    p.alliances.al = al;
    return p;
}

int main() {
    // 1. No alliance: the self bit alone, at the VECTOR index.
    for (std::size_t i = 0; i < 8; ++i) {
        const Player p = MakePlayer(static_cast<int>(i), sots::app::kNoAlliance, 0);
        CHECK_EQ(sots::app::AllianceMask(p, i), 1 << i);
    }

    // 2. The index field disagrees with the vector position. The original shifts by the loop
    // variable and never loads the index field, so the vector position wins. No save in the
    // corpus has these two apart; this is the instruction-stream reading, pinned.
    {
        const Player p = MakePlayer(/*plyrIdx=*/7, sots::app::kNoAlliance, 0);
        CHECK_EQ(sots::app::AllianceMask(p, 2), 1 << 2);
    }

    // 3. In an alliance whose member mask does NOT already contain the player's own bit.
    // Every alliance in the corpus does contain it, so `self | AL` and `AL` are the same
    // number there. Here they are not, and the OR is what is being held.
    {
        const Player p = MakePlayer(/*plyrIdx=*/1, /*alid=*/0, /*al=*/0x0c);  // bits 2 and 3
        CHECK_EQ(sots::app::AllianceMask(p, 1), 0x0e);                       // 1|2|3
    }

    // 4. The guard is the alliance id, not the member mask. A stale member mask with no
    // alliance id contributes nothing. Unobserved in the corpus, where the two never differ.
    {
        const Player p = MakePlayer(/*plyrIdx=*/1, sots::app::kNoAlliance, /*al=*/0x0c);
        CHECK_EQ(sots::app::AllianceMask(p, 1), 0x02);
    }

    // 5. An alliance id of zero is a real alliance. -1 is the only "none", and a check
    // written as `if (alid)` would drop every player of alliance 0 -- which is the only
    // alliance id that appears anywhere in the corpus.
    {
        const Player p = MakePlayer(/*plyrIdx=*/2, /*alid=*/0, /*al=*/0x0c);
        CHECK_EQ(sots::app::AllianceMask(p, 2), 0x0c);
    }

    // 6. The whole phase, in vector order, and the shape the corpus actually shows: two
    // allied players carrying the same member mask, the rest alone.
    {
        std::vector<PlayerEntry> players(8);
        for (std::size_t i = 0; i < players.size(); ++i)
            players[i].player = MakePlayer(static_cast<int>(i), sots::app::kNoAlliance, 0);
        players[2].player = MakePlayer(2, 0, 0x0c);
        players[3].player = MakePlayer(3, 0, 0x0c);
        const std::vector<std::int32_t> m = sots::app::RebuildAllianceMasks(players);
        CHECK_EQ(m.size(), players.size());
        const std::int32_t want[8] = {1, 2, 0x0c, 0x0c, 0x10, 0x20, 0x40, 0x80};
        for (std::size_t i = 0; i < 8; ++i) CHECK_EQ(m[i], want[i]);
    }

    // 7. The shift wraps above 31, because x86 masks a variable shift count to five bits.
    // Untested against any game -- no save has more than eight players -- and reproduced
    // rather than corrected, so that a reimplementation running a 32-player game diverges the
    // same way the original does instead of diverging differently.
    {
        const Player p = MakePlayer(0, sots::app::kNoAlliance, 0);
        CHECK_EQ(sots::app::AllianceMask(p, 32), 1);
        CHECK_EQ(sots::app::AllianceMask(p, 33), 2);
    }

    std::printf("app_test_alliance: %d failure(s)\n", failures);
    return failures ? 1 : 0;
}