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Tracking down imp desync #4672

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9bcc3e4
analysis
rainlizard Apr 14, 2026
bd1b185
log desynced seed function
rainlizard Apr 14, 2026
ee7813e
imp log
rainlizard Apr 14, 2026
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2 changes: 2 additions & 0 deletions src/game_legacy.h
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Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,8 @@ struct LogThingDesyncInfo {
struct CoordDelta3d veloc_base;
struct CoordDelta3d veloc_push_once;
struct CoordDelta3d veloc_push_add;
TbBool is_creature;
struct Coord3d moveto_pos;
TbBool is_special_digger;
struct Coord3d digger_moveto_pos;
short digger_dragtng_idx;
Expand Down
13 changes: 12 additions & 1 deletion src/game_merge.h
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Expand Up @@ -52,8 +52,19 @@ extern "C" {

// Random number generation system with synchronized and unsynchronized variants

void imp_random_log_push(uint16_t thing_idx, const char *func, unsigned long line, unsigned long range, unsigned long result, unsigned long seed_after);

static inline unsigned long thing_random_impl(struct Thing *thing, unsigned long range, const char *func_name, unsigned long line)
{
unsigned long result = LbRandomSeries(range, &thing->random_seed, func_name, line);
if (thing_is_creature_special_digger(thing)) {
imp_random_log_push(thing->index, func_name, line, range, result, (unsigned long)thing->random_seed);
}
return result;
}

// Thing-specific random for deterministic per-thing behavior (creatures, objects, etc.)
#define THING_RANDOM(thing, range) LbRandomSeries(range, &((struct Thing*)(thing))->random_seed, __func__, __LINE__)
#define THING_RANDOM(thing, range) thing_random_impl((struct Thing*)(thing), range, __func__, __LINE__)
// Global game events requiring synchronization across network (scripts, AI decisions, player events)
#define GAME_RANDOM(range) LbRandomSeries(range, &game.action_random_seed, __func__, __LINE__)
// Unsynchronized random for visual/audio effects that don't affect game state (lighting, particles)
Expand Down
71 changes: 68 additions & 3 deletions src/net_checksums.c
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Expand Up @@ -40,6 +40,49 @@ extern "C" {
/******************************************************************************/
#define CHECKSUM_ADD(checksum, value) checksum = ((checksum << 5) | (checksum >> 27)) ^ (ulong)(value)
#define SNAPSHOT_BUFFER_SIZE 15
#define IMP_RANDOM_LOG_SIZE 16384

struct ImpRandomEntry {
const char *func;
unsigned long line;
unsigned long range;
unsigned long result;
unsigned long seed_after;
uint16_t thing_idx;
};

static struct ImpRandomEntry imp_random_log[IMP_RANDOM_LOG_SIZE];
static int imp_random_log_pos = 0;
static int imp_random_log_count = 0;

void imp_random_log_push(uint16_t thing_idx, const char *func, unsigned long line, unsigned long range, unsigned long result, unsigned long seed_after)
{
struct ImpRandomEntry *entry = &imp_random_log[imp_random_log_pos];
entry->thing_idx = thing_idx;
entry->func = func;
entry->line = line;
entry->range = range;
entry->result = result;
entry->seed_after = seed_after;
imp_random_log_pos = (imp_random_log_pos + 1) % IMP_RANDOM_LOG_SIZE;
if (imp_random_log_count < IMP_RANDOM_LOG_SIZE) {
imp_random_log_count++;
}
}

void imp_random_log_dump(uint16_t thing_idx)
{
ERRORLOG(" Imp Thing[%u] THING_RANDOM history (last %d entries):", (unsigned)thing_idx, imp_random_log_count);
int start = (imp_random_log_pos - imp_random_log_count + IMP_RANDOM_LOG_SIZE) % IMP_RANDOM_LOG_SIZE;
for (int i = 0; i < imp_random_log_count; i++) {
struct ImpRandomEntry *entry = &imp_random_log[(start + i) % IMP_RANDOM_LOG_SIZE];
if (entry->thing_idx != thing_idx) {
continue;
}
ERRORLOG(" Thing[%u] %s:%lu range=%lu result=%lu seed_after=%08lx",
(unsigned)entry->thing_idx, entry->func, entry->line, entry->range, entry->result, entry->seed_after);
}
}

struct ChecksumSnapshot {
GameTurn turn;
Expand Down Expand Up @@ -86,11 +129,14 @@ TbBigChecksum get_thing_checksum(const struct Thing* thing) {
CHECKSUM_ADD(checksum, thing->veloc_push_add.x.val);
CHECKSUM_ADD(checksum, thing->veloc_push_add.y.val);
CHECKSUM_ADD(checksum, thing->veloc_push_add.z.val);
if (thing_is_creature_special_digger(thing)) {
if (thing->class_id == TCls_Creature) {
struct CreatureControl* cctrl = creature_control_get_from_thing(thing);
CHECKSUM_ADD(checksum, cctrl->moveto_pos.x.val);
CHECKSUM_ADD(checksum, cctrl->moveto_pos.y.val);
CHECKSUM_ADD(checksum, cctrl->moveto_pos.z.val);
}
if (thing_is_creature_special_digger(thing)) {
struct CreatureControl* cctrl = creature_control_get_from_thing(thing);
CHECKSUM_ADD(checksum, cctrl->dragtng_idx);
CHECKSUM_ADD(checksum, cctrl->arming_thing_id);
CHECKSUM_ADD(checksum, cctrl->pickup_object_id);
Expand Down Expand Up @@ -255,6 +301,11 @@ void update_turn_checksums(void) {
thing_snapshot->veloc_base = thing->veloc_base;
thing_snapshot->veloc_push_once = thing->veloc_push_once;
thing_snapshot->veloc_push_add = thing->veloc_push_add;
thing_snapshot->is_creature = (thing->class_id == TCls_Creature);
if (thing_snapshot->is_creature) {
struct CreatureControl* cctrl = creature_control_get_from_thing(thing);
thing_snapshot->moveto_pos = cctrl->moveto_pos;
}
thing_snapshot->is_special_digger = thing_is_creature_special_digger(thing);
if (thing_snapshot->is_special_digger) {
struct CreatureControl* cctrl = creature_control_get_from_thing(thing);
Expand Down Expand Up @@ -338,6 +389,11 @@ void pack_desync_history_for_resync(void) {
}
game.host_checksums = snapshot->checksums;
game.log_snapshot = snapshot->log_details;
for (int i = 0; i < game.log_snapshot.thing_count; i++) {
if (game.log_snapshot.things[i].is_special_digger) {
imp_random_log_dump(game.log_snapshot.things[i].index);
}
}
}

static void log_thing_differences(struct LogDetailedSnapshot* client, const char* name, TbBigChecksum client_sum, TbBigChecksum host_sum, ThingClass filter_class) {
Expand Down Expand Up @@ -388,9 +444,17 @@ static void log_thing_differences(struct LogDetailedSnapshot* client, const char
(long)client_thing->veloc_base.x.val, (long)client_thing->veloc_base.y.val, (long)client_thing->veloc_base.z.val,
(long)client_thing->veloc_push_once.x.val, (long)client_thing->veloc_push_once.y.val, (long)client_thing->veloc_push_once.z.val,
(long)client_thing->veloc_push_add.x.val, (long)client_thing->veloc_push_add.y.val, (long)client_thing->veloc_push_add.z.val);
if (client_thing->is_creature) {
if (host_thing != NULL) {
ERRORLOG(" [Host] moveto_pos=(%ld,%ld,%ld)",
(long)host_thing->moveto_pos.x.val, (long)host_thing->moveto_pos.y.val, (long)host_thing->moveto_pos.z.val);
}
ERRORLOG(" [Client] moveto_pos=(%ld,%ld,%ld)",
(long)client_thing->moveto_pos.x.val, (long)client_thing->moveto_pos.y.val, (long)client_thing->moveto_pos.z.val);
}
if (client_thing->is_special_digger) {
if (host_thing != NULL) {
ERRORLOG(" [Host] digger moveto=(%ld,%ld,%ld) dragtng=%d arming=%d pickup_obj=%d pickup_cr=%d move_flags=%u stack_update_turn=%ld working_stl=%u task_stl=%u task_idx=%u consecutive_reinforcements=%u last_did_job=%u task_stack_pos=%u task_repeats=%u",
ERRORLOG(" [Host] digger_moveto_pos=(%ld,%ld,%ld) dragtng_idx=%d arming_thing_id=%d pickup_object_id=%d pickup_creature_id=%d move_flags=%u stack_update_turn=%ld working_stl=%u task_stl=%u task_idx=%u consecutive_reinforcements=%u last_did_job=%u task_stack_pos=%u task_repeats=%u",
(long)host_thing->digger_moveto_pos.x.val, (long)host_thing->digger_moveto_pos.y.val, (long)host_thing->digger_moveto_pos.z.val,
(int)host_thing->digger_dragtng_idx, (int)host_thing->digger_arming_thing_id,
(int)host_thing->digger_pickup_object_id, (int)host_thing->digger_pickup_creature_id,
Expand All @@ -400,7 +464,7 @@ static void log_thing_differences(struct LogDetailedSnapshot* client, const char
(unsigned)host_thing->digger_last_did_job,
(unsigned)host_thing->digger_task_stack_pos, (unsigned)host_thing->digger_task_repeats);
}
ERRORLOG(" [Client] digger moveto=(%ld,%ld,%ld) dragtng=%d arming=%d pickup_obj=%d pickup_cr=%d move_flags=%u stack_update_turn=%ld working_stl=%u task_stl=%u task_idx=%u consecutive_reinforcements=%u last_did_job=%u task_stack_pos=%u task_repeats=%u",
ERRORLOG(" [Client] digger_moveto_pos=(%ld,%ld,%ld) dragtng_idx=%d arming_thing_id=%d pickup_object_id=%d pickup_creature_id=%d move_flags=%u stack_update_turn=%ld working_stl=%u task_stl=%u task_idx=%u consecutive_reinforcements=%u last_did_job=%u task_stack_pos=%u task_repeats=%u",
(long)client_thing->digger_moveto_pos.x.val, (long)client_thing->digger_moveto_pos.y.val, (long)client_thing->digger_moveto_pos.z.val,
(int)client_thing->digger_dragtng_idx, (int)client_thing->digger_arming_thing_id,
(int)client_thing->digger_pickup_object_id, (int)client_thing->digger_pickup_creature_id,
Expand All @@ -409,6 +473,7 @@ static void log_thing_differences(struct LogDetailedSnapshot* client, const char
(unsigned)client_thing->digger_task_idx, (unsigned)client_thing->digger_consecutive_reinforcements,
(unsigned)client_thing->digger_last_did_job,
(unsigned)client_thing->digger_task_stack_pos, (unsigned)client_thing->digger_task_repeats);
imp_random_log_dump(client_thing->index);
}
shown++;
}
Expand Down
2 changes: 2 additions & 0 deletions src/net_checksums.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,8 @@ TbBigChecksum get_thing_checksum(const struct Thing *thing);
short checksums_different(void);
CoroutineLoopState perform_checksum_verification(CoroutineLoop *con);
CoroutineLoopState verify_sprite_zip_checksums(CoroutineLoop *con);
void imp_random_log_push(uint16_t thing_idx, const char *func, unsigned long line, unsigned long range, unsigned long result, unsigned long seed_after);
void imp_random_log_dump(uint16_t thing_idx);

/******************************************************************************/
#ifdef __cplusplus
Expand Down
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