fix: address PR review - rolling adler32, extract helpers, configurable max file size

- Fix rolling adler32: add missing -1 in s2 update formula (was producing
  wrong checksums, causing zero block matches)
- Fix file_send_sendfile signature to match typedef (add unused
  compression_level param)
- Extract receive_delta_file() from receive_incremental_check() to reduce
  nesting depth
- Extract send_file_incremental() helper in client_send.c
- Add delta_max_file_size to Config, serialized over wire
- Add --delta-max CLI flag
- Add test_large_file_delta (200KB) and extra delta_should_attempt cases
- Remove unused pos_in_block variable from delta_compute

src/client/client_cli.c

@@ -39,6 +39,7 @@ static void print_usage(void) {
   printf("  --incremental       Skip files unchanged since last transfer\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
   printf("  --delta-block <n>   Delta block size in bytes (default: %d)\n", DELTA_BLOCK_SIZE_DEFAULT);
+  printf("  --delta-max <n>     Max file size for delta transfer (default: %llu)\n", DELTA_MAX_FILE_SIZE);
   printf("  -m                  Enable multithreading\n");
   printf("  -s                  Enable chunk serialization\n");
   printf("  -f                  Enable sendfile (TCP only, not with -c or -s)\n");
@@ -112,6 +113,12 @@ int main(int argc, char *argv[]) {
         config->delta_block_size = (uint32_t)val;
       else
         fprintf(stderr, "Warning: --delta-block value %llu out of range, using default\n", val);
+    } else if (strcmp(argv[i], "--delta-max") == 0 && i + 1 < argc) {
+      unsigned long long val = strtoull(argv[++i], NULL, 10);
+      if (val >= DELTA_MIN_FILE_SIZE)
+        config->delta_max_file_size = val;
+      else
+        fprintf(stderr, "Warning: --delta-max value %llu too small, using default\n", val);
     } else if (strcmp(argv[i], "-c") == 0 || strcmp(argv[i], "-z") == 0) {
       config->use_compression = true;
       log_message(LOG_LEVEL_INFO, "Enabled Compression");

src/client/client_send.c

@@ -87,6 +87,28 @@ static int send_delta(Client *client, File *file, DeltaSignature *sig,
   return ok ? 0 : -1;
 }
 
+typedef bool (*file_send_fn)(File *, int, bool, int, bool);
+
+static int send_file_incremental(Client *client, File *file, Config *config,
+                                  file_send_fn send_fn) {
+  DeltaSignature *sig = NULL;
+  int rc = incremental_check(client, file, &sig);
+  if (rc < 0) { delta_signature_destroy(sig); return -1; }
+  if (rc == 1) { delta_signature_destroy(sig); return 1; }
+  if (rc == 2 && config->use_delta) {
+    int drc = send_delta(client, file, sig, config);
+    delta_signature_destroy(sig);
+    if (drc == 0) return 0;
+    if (drc < 0) return -1;
+  } else {
+    delta_signature_destroy(sig);
+  }
+  if (!send_fn(file, client->file_descriptor, config->use_metadata,
+               config->use_compression ? config->compression_level : 0, false))
+    return -1;
+  return 0;
+}
+
 int send_chunk(Client *client, Chunk *chunk, Config *config) {
   if (config->use_chunk_serialization) {
     if (!send_status(client->file_descriptor, STATUS_CHUNK)) return -1;
@@ -102,46 +124,23 @@ int send_chunk(Client *client, Chunk *chunk, Config *config) {
   } else if (config->use_sendfile && !config->use_compression) {
     for (int i = 0; i < chunk->element_count; i++) {
       if (config->use_incremental) {
-        DeltaSignature *sig = NULL;
-        int rc = incremental_check(client, chunk->items[i], &sig);
-        if (rc < 0) { delta_signature_destroy(sig); return -1; }
-        if (rc == 1) { delta_signature_destroy(sig); continue; }
-        if (rc == 2 && config->use_delta) {
-          int drc = send_delta(client, chunk->items[i], sig, config);
-          delta_signature_destroy(sig);
-          if (drc == 0) continue;
-          if (drc < 0) return -1;
-        } else {
-          delta_signature_destroy(sig);
-        }
-        if (!file_send_sendfile(chunk->items[i], client->file_descriptor, config->use_metadata, false))
-          return -1;
+        int rc = send_file_incremental(client, chunk->items[i], config,
+                                        (file_send_fn)file_send_sendfile);
+        if (rc == 1) continue;
+        if (rc < 0) return -1;
       } else {
         if (!send_status(client->file_descriptor, STATUS_NEXT)) return -1;
-        if (!file_send_sendfile(chunk->items[i], client->file_descriptor, config->use_metadata, true))
+        if (!file_send_sendfile(chunk->items[i], client->file_descriptor, config->use_metadata, 0, true))
           return -1;
       }
     }
   } else {
     for (int i = 0; i < chunk->element_count; i++) {
       if (config->use_incremental) {
-        DeltaSignature *sig = NULL;
-        int rc = incremental_check(client, chunk->items[i], &sig);
-        if (rc < 0) { delta_signature_destroy(sig); return -1; }
-        if (rc == 1) { delta_signature_destroy(sig); continue; }
-        if (rc == 2 && config->use_delta) {
-          int drc = send_delta(client, chunk->items[i], sig, config);
-          delta_signature_destroy(sig);
-          if (drc == 0) continue;
-          if (drc < 0) return -1;
-        } else {
-          delta_signature_destroy(sig);
-        }
-        if (!file_send_single_calls(chunk->items[i], client->file_descriptor,
-                                   config->use_metadata,
-                                   config->use_compression ? config->compression_level : 0,
-                                   false))
-          return -1;
+        int rc = send_file_incremental(client, chunk->items[i], config,
+                                        (file_send_fn)file_send_single_calls);
+        if (rc == 1) continue;
+        if (rc < 0) return -1;
       } else {
         if (!send_status(client->file_descriptor, STATUS_NEXT)) return -1;
         if (!file_send_single_calls(chunk->items[i], client->file_descriptor,

src/shared/config.c

@@ -42,6 +42,7 @@ Config *config_create(char *version, char *send_directory,
   config->use_incremental = false;
   config->use_delta = false;
   config->delta_block_size = DELTA_BLOCK_SIZE_DEFAULT;
+  config->delta_max_file_size = DELTA_MAX_FILE_SIZE;
   config->use_tls = false;
   config->tls_cert = NULL;
   config->tls_key = NULL;
@@ -103,6 +104,7 @@ bool config_send(int file_descriptor, Config *config) {
   if (!send_int(file_descriptor, config->use_incremental)) return false;
   if (!send_int(file_descriptor, config->use_delta)) return false;
   if (!send_int(file_descriptor, (int)config->delta_block_size)) return false;
+  if (!send_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long))) return false;
   Status status;
   if (!receive_status(file_descriptor, &status)) return false;
   if (status != STATUS_OK) {
@@ -154,6 +156,7 @@ Config *config_receive(int file_descriptor) {
   config->use_delta = tmp;
   if (!receive_int(file_descriptor, &tmp)) goto error;
   config->delta_block_size = (uint32_t)tmp;
+  if (!receive_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long))) goto error;
   config->show_progress = false;
   config->dry_run = false;
   config->ssh_port = 22;

src/shared/config.h

@@ -36,6 +36,7 @@ typedef struct Config {
   bool use_incremental;
   bool use_delta;
   uint32_t delta_block_size;
+  unsigned long long delta_max_file_size;
   bool use_tls;
   char *tls_cert;
   char *tls_key;

src/shared/delta.c

@@ -128,6 +128,33 @@ void delta_signature_destroy(DeltaSignature *sig) {
   free(sig);
 }
 
+static bool ensure_capacity(DeltaInstruction **instrs, uint32_t *capacity,
+                             uint32_t count) {
+  if (count < *capacity) return true;
+  uint32_t new_cap = *capacity * 2;
+  DeltaInstruction *tmp = realloc(*instrs, new_cap * sizeof(DeltaInstruction));
+  if (!tmp) return false;
+  *instrs = tmp;
+  *capacity = new_cap;
+  return true;
+}
+
+static bool flush_literal(DeltaInstruction **instrs, uint32_t *capacity,
+                           uint32_t *count, const uint8_t *data,
+                           uint64_t start, uint64_t end) {
+  if (start >= end) return true;
+  uint32_t lit_len = (uint32_t)(end - start);
+  if (!ensure_capacity(instrs, capacity, *count)) return false;
+  uint8_t *lit_data = malloc(lit_len);
+  if (!lit_data) return false;
+  memcpy(lit_data, data + start, lit_len);
+  (*instrs)[*count].type = DELTA_INSTR_LITERAL;
+  (*instrs)[*count].literal.data = lit_data;
+  (*instrs)[*count].literal.length = lit_len;
+  (*count)++;
+  return true;
+}
+
 Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
                       const DeltaSignature *sig, uint32_t block_size) {
   if (!new_file_data || !sig || new_file_size == 0 || block_size == 0)
@@ -144,39 +171,55 @@ Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
   bool has_literal = false;
 
   uint64_t i = 0;
+
+  uint32_t s1 = 1, s2 = 0;
+  bool rolling_valid = false;
+
   while (i < new_file_size) {
     uint32_t window_len = (uint32_t)((new_file_size - i < block_size)
                                          ? (new_file_size - i)
                                          : block_size);
-    uint32_t adler = delta_adler32(new_data + i, window_len);
-    uint32_t xxh = delta_xxhash32(new_data + i, window_len);
+    bool full_window = (window_len == block_size);
+
+    uint32_t adler;
+    if (rolling_valid && full_window) {
+      uint8_t old_byte = new_data[i - 1];
+      uint8_t new_byte = new_data[i + block_size - 1];
+      s1 = (s1 + DELTA_ADLER32_MODULUS - old_byte + new_byte) %
+           DELTA_ADLER32_MODULUS;
+      s2 = (s2 + DELTA_ADLER32_MODULUS -
+            (uint32_t)((uint64_t)block_size * old_byte % DELTA_ADLER32_MODULUS) +
+            s1 - 1) %
+           DELTA_ADLER32_MODULUS;
+      adler = (s2 << 16) | s1;
+    } else {
+      s1 = 1;
+      s2 = 0;
+      for (uint32_t k = 0; k < window_len; k++) {
+        s1 = (s1 + new_data[i + k]) % DELTA_ADLER32_MODULUS;
+        s2 = (s2 + s1) % DELTA_ADLER32_MODULUS;
+      }
+      adler = (s2 << 16) | s1;
+      rolling_valid = full_window;
+    }
 
     bool matched = false;
     for (uint32_t j = 0; j < sig->block_count; j++) {
-      if (adler == sig->blocks[j].adler32 && xxh == sig->blocks[j].xxhash) {
+      if (adler == sig->blocks[j].adler32 && full_window) {
+        uint32_t xxh = delta_xxhash32(new_data + i, window_len);
+        if (xxh == sig->blocks[j].xxhash) {
           if (has_literal) {
-          uint32_t lit_len = (uint32_t)(i - literal_start);
-          if (count == capacity) {
-            capacity *= 2;
-            DeltaInstruction *tmp = realloc(instrs, capacity * sizeof(DeltaInstruction));
-            if (!tmp) { free(instrs); return NULL; }
-            instrs = tmp;
+            if (!flush_literal(&instrs, &capacity, &count, new_data,
+                               literal_start, i)) {
+              free(instrs);
+              return NULL;
             }
-          uint8_t *lit_data = malloc(lit_len);
-          if (!lit_data) { free(instrs); return NULL; }
-          memcpy(lit_data, new_data + literal_start, lit_len);
-          instrs[count].type = DELTA_INSTR_LITERAL;
-          instrs[count].literal.data = lit_data;
-          instrs[count].literal.length = lit_len;
-          count++;
             has_literal = false;
           }
 
-        if (count == capacity) {
-          capacity *= 2;
-          DeltaInstruction *tmp = realloc(instrs, capacity * sizeof(DeltaInstruction));
-          if (!tmp) { free(instrs); return NULL; }
-          instrs = tmp;
+          if (!ensure_capacity(&instrs, &capacity, count)) {
+            free(instrs);
+            return NULL;
           }
           instrs[count].type = DELTA_INSTR_BLOCK_MATCH;
           instrs[count].match.block_index = j;
@@ -185,10 +228,12 @@ Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
           count++;
 
           i += window_len;
+          rolling_valid = false;
           matched = true;
           break;
         }
       }
+    }
 
     if (!matched) {
       if (!has_literal) {
@@ -200,20 +245,11 @@ Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
   }
 
   if (has_literal) {
-    uint32_t lit_len = (uint32_t)(new_file_size - literal_start);
-    if (count == capacity) {
-      capacity *= 2;
-      DeltaInstruction *tmp = realloc(instrs, capacity * sizeof(DeltaInstruction));
-      if (!tmp) { free(instrs); return NULL; }
-      instrs = tmp;
+    if (!flush_literal(&instrs, &capacity, &count, new_data,
+                       literal_start, new_file_size)) {
+      free(instrs);
+      return NULL;
     }
-    uint8_t *lit_data = malloc(lit_len);
-    if (!lit_data) { free(instrs); return NULL; }
-    memcpy(lit_data, new_data + literal_start, lit_len);
-    instrs[count].type = DELTA_INSTR_LITERAL;
-    instrs[count].literal.data = lit_data;
-    instrs[count].literal.length = lit_len;
-    count++;
   }
 
   Delta *delta = malloc(sizeof(Delta));
@@ -421,10 +457,10 @@ void delta_destroy(Delta *delta) {
   free(delta);
 }
 
-bool delta_should_attempt(uint64_t old_size, uint64_t new_size) {
+bool delta_should_attempt(uint64_t old_size, uint64_t new_size, uint64_t max_file_size) {
   if (old_size < DELTA_MIN_FILE_SIZE || new_size < DELTA_MIN_FILE_SIZE)
     return false;
-  if (old_size > DELTA_MAX_FILE_SIZE || new_size > DELTA_MAX_FILE_SIZE)
+  if (old_size > max_file_size || new_size > max_file_size)
     return false;
   double large = (old_size > new_size) ? (double)old_size : (double)new_size;
   double small = (old_size > new_size) ? (double)new_size : (double)old_size;

src/shared/delta.h

@@ -72,7 +72,7 @@ void *delta_apply(const void *old_data, uint64_t old_size, const Delta *delta,
                   uint32_t block_size);
 void delta_destroy(Delta *delta);
 
-bool delta_should_attempt(uint64_t old_size, uint64_t new_size);
+bool delta_should_attempt(uint64_t old_size, uint64_t new_size, uint64_t max_file_size);
 bool delta_is_worthwhile(const Delta *delta, uint64_t new_file_size);
 
 uint32_t delta_adler32(const void *data, uint32_t len);

src/shared/file.c

@@ -133,87 +133,38 @@ bool file_save_to_disk(const char *root_directory, File *file) {
   return ok;
 }
 
-File *receive_incremental_check(int fd, Config *config, bool *skipped) {
-  *skipped = false;
-  char *check_path = receive_str(fd);
-  if (check_path == NULL) { send_status(fd, STATUS_ERROR); return NULL; }
-
-  unsigned long long check_size;
-  long long check_mtime;
-  if (!receive_n_data(fd, &check_size, sizeof(check_size)) ||
-      !receive_n_data(fd, &check_mtime, sizeof(check_mtime))) {
-    free(check_path);
-    send_status(fd, STATUS_ERROR);
-    return NULL;
-  }
-
-  char *full_path = path_cat(config->receive_root_directory, check_path);
-  struct stat st;
-  bool has_old_file = (full_path && stat(full_path, &st) == 0);
-  unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;
-
-  bool match = has_old_file &&
-               (unsigned long long)st.st_size == check_size &&
-               (long long)st.st_mtime == check_mtime;
-
-  if (match) {
-    if (!send_status(fd, STATUS_OK)) { free(full_path); free(check_path); return NULL; }
-    free(full_path);
-    free(check_path);
-    *skipped = true;
-    return NULL;
-  }
-
-  bool try_delta = config->use_delta && has_old_file &&
-                   delta_should_attempt(old_size, check_size);
-
-  if (try_delta) {
-    void *old_data = malloc((size_t)old_size);
-    if (!old_data) {
-      try_delta = false;
-    } else {
+static void *old_data_from_path(const char *full_path, unsigned long long old_size) {
+  void *data = malloc((size_t)old_size);
+  if (!data) return NULL;
   FILE *fp = fopen(full_path, "rb");
-      if (!fp) {
-        free(old_data);
-        try_delta = false;
-      } else {
-        size_t nread = fread(old_data, 1, (size_t)old_size, fp);
+  if (!fp) { free(data); return NULL; }
+  size_t nread = fread(data, 1, (size_t)old_size, fp);
   fclose(fp);
-        if (nread != (size_t)old_size) {
-          free(old_data);
-          try_delta = false;
-        }
-      }
+  if (nread != (size_t)old_size) { free(data); return NULL; }
+  return data;
 }
 
-    if (try_delta) {
+static File *receive_delta_file(int fd, Config *config, const char *check_path,
+                                 void *old_data, unsigned long long old_size) {
+  if (!old_data) return NULL;
+
   DeltaSignature *sig = delta_signature_create(old_data, old_size,
                                                 config->delta_block_size);
-      if (!sig) {
-        free(old_data);
-        try_delta = false;
-      } else {
+  if (!sig) { free(old_data); return NULL; }
+
   Data *sig_data = delta_signature_serialize(sig);
-        if (!sig_data) {
-          delta_signature_destroy(sig);
-          free(old_data);
-          try_delta = false;
-        } else {
+  if (!sig_data) { delta_signature_destroy(sig); free(old_data); return NULL; }
+
   bool sig_sent = send_status(fd, STATUS_DELTA_SIGNATURE) &&
                   send_data(fd, sig_data);
   data_destroy(sig_data);
 
-          if (!sig_sent) {
-            delta_signature_destroy(sig);
-            free(old_data);
-            try_delta = false;
-          } else {
+  if (!sig_sent) { delta_signature_destroy(sig); free(old_data); return NULL; }
+
   Status resp;
   if (!receive_status(fd, &resp)) {
     delta_signature_destroy(sig);
     free(old_data);
-              free(full_path);
-              free(check_path);
     return NULL;
   }
 
@@ -223,8 +174,6 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
       delta_signature_destroy(sig);
       free(old_data);
       send_status(fd, STATUS_ERROR);
-                free(full_path);
-                free(check_path);
       return NULL;
     }
 
@@ -236,8 +185,6 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
         free(old_data);
         delta_signature_destroy(sig);
         send_status(fd, STATUS_ERROR);
-                  free(full_path);
-                  free(check_path);
         return NULL;
       }
     }
@@ -248,8 +195,6 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
       free(old_data);
       delta_signature_destroy(sig);
       send_status(fd, STATUS_ERROR);
-                free(full_path);
-                free(check_path);
       return NULL;
     }
 
@@ -262,15 +207,10 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
       free(old_data);
       delta_signature_destroy(sig);
       send_status(fd, STATUS_ERROR);
-                free(full_path);
-                free(check_path);
       return NULL;
     }
 
     File *file = file_create(check_path);
-              free(check_path);
-              free(full_path);
-
     if (!file) {
       free(new_data);
       free(old_data);
@@ -305,8 +245,6 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
     free(old_data);
 
     File *file = file_create(check_path);
-              free(check_path);
-              free(full_path);
     if (!file) { send_status(fd, STATUS_ERROR); return NULL; }
 
     if (config->use_metadata) {
@@ -336,12 +274,54 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
 
   delta_signature_destroy(sig);
   free(old_data);
+  return NULL;
+}
+
+File *receive_incremental_check(int fd, Config *config, bool *skipped) {
+  *skipped = false;
+  char *check_path = receive_str(fd);
+  if (check_path == NULL) { send_status(fd, STATUS_ERROR); return NULL; }
+
+  unsigned long long check_size;
+  long long check_mtime;
+  if (!receive_n_data(fd, &check_size, sizeof(check_size)) ||
+      !receive_n_data(fd, &check_mtime, sizeof(check_mtime))) {
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+
+  char *full_path = path_cat(config->receive_root_directory, check_path);
+  struct stat st;
+  bool has_old_file = (full_path && stat(full_path, &st) == 0);
+  unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;
+
+  bool match = has_old_file &&
+               (unsigned long long)st.st_size == check_size &&
+               (long long)st.st_mtime == check_mtime;
+
+  if (match) {
+    if (!send_status(fd, STATUS_OK)) { free(full_path); free(check_path); return NULL; }
+    free(full_path);
+    free(check_path);
+    *skipped = true;
+    return NULL;
+  }
+
+  bool try_delta = config->use_delta && has_old_file &&
+                   delta_should_attempt(old_size, check_size, config->delta_max_file_size);
+
+  if (try_delta) {
+    void *old_data = old_data_from_path(full_path, old_size);
+    File *delta_file = receive_delta_file(fd, config, check_path,
+                                           old_data, old_size);
+    if (delta_file) {
+      free(full_path);
+      free(check_path);
+      return delta_file;
+    }
     try_delta = false;
   }
-        }
-      }
-    }
-  }
 
   if (!try_delta) {
     if (!send_status(fd, STATUS_NEXT)) {
@@ -406,7 +386,8 @@ bool to_disk(const char *path, const void *data, unsigned long long data_size) {
   return true;
 }
 
-bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, bool send_path) {
+bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, int compression_level, bool send_path) {
+  (void)compression_level;
   if (send_path && !send_str(file_descriptor, file->path)) return false;
   if (use_metadata && !metadata_send(file_descriptor, file->metadata)) return false;
 

src/shared/file.h

@@ -25,7 +25,7 @@ void file_destroy(void *item);
 bool file_load_data(File *file);
 File *file_receive(Config *config, int file_descriptor);
 bool file_send_single_calls(File *file, int file_descriptor, bool use_metadata, int compression_level, bool send_path);
-bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, bool send_path);
+bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, int compression_level, bool send_path);
 size_t file_content_to_buffer(File *file);
 FileMetadata *file_metadata_create(struct stat *stats);
 void file_metadata_destroy(void *metadata);

tests/test_delta.c

@@ -238,12 +238,14 @@ static void test_delta_file_shrink() {
 }
 
 static void test_should_attempt() {
-  EXPECT_TRUE(delta_should_attempt(100000, 100000));
-  EXPECT_TRUE(!delta_should_attempt(100, 100));
-  EXPECT_TRUE(!delta_should_attempt(100000, 10));
-  EXPECT_TRUE(!delta_should_attempt(300000000, 300000000));
-  EXPECT_TRUE(delta_should_attempt(50000, 60000));
-  EXPECT_TRUE(!delta_should_attempt(50000, 600000));
+  EXPECT_TRUE(delta_should_attempt(100000, 100000, DELTA_MAX_FILE_SIZE));
+  EXPECT_TRUE(!delta_should_attempt(100, 100, DELTA_MAX_FILE_SIZE));
+  EXPECT_TRUE(!delta_should_attempt(100000, 10, DELTA_MAX_FILE_SIZE));
+  EXPECT_TRUE(!delta_should_attempt(300000000, 300000000, DELTA_MAX_FILE_SIZE));
+  EXPECT_TRUE(delta_should_attempt(50000, 60000, DELTA_MAX_FILE_SIZE));
+  EXPECT_TRUE(!delta_should_attempt(50000, 600000, DELTA_MAX_FILE_SIZE));
+  EXPECT_TRUE(delta_should_attempt(50000, 60000, 500000));
+  EXPECT_TRUE(!delta_should_attempt(100000, 100000, 50000));
 }
 
 static void test_is_worthwhile() {
@@ -266,6 +268,54 @@ static void test_is_worthwhile() {
   EXPECT_TRUE(!delta_is_worthwhile(NULL, 1000));
 }
 
+static void test_large_file_delta() {
+  uint32_t block_size = 8192;
+  uint64_t old_size = 200000;
+  uint64_t new_size = 200000;
+
+  void *old_data = malloc((size_t)old_size);
+  void *new_data = malloc((size_t)new_size);
+  EXPECT_TRUE(old_data != NULL && new_data != NULL);
+
+  for (uint64_t i = 0; i < old_size; i++)
+    ((uint8_t *)old_data)[i] = (uint8_t)(i % 251);
+  memcpy(new_data, old_data, (size_t)old_size);
+
+  uint64_t offset = 100000;
+  uint32_t change_len = 4096;
+  for (uint32_t i = 0; i < change_len; i++)
+    ((uint8_t *)new_data)[offset + i] = (uint8_t)((i * 7 + 13) % 256);
+
+  DeltaSignature *sig = delta_signature_create(old_data, old_size, block_size);
+  EXPECT_TRUE(sig != NULL);
+  EXPECT_TRUE(sig->block_count == (uint32_t)((old_size + block_size - 1) / block_size));
+
+  Delta *delta = delta_compute(new_data, new_size, sig, block_size);
+  EXPECT_TRUE(delta != NULL);
+
+  uint64_t total_literal = 0;
+  uint32_t match_count = 0;
+  for (uint32_t i = 0; i < delta->instruction_count; i++) {
+    if (delta->instructions[i].type == DELTA_INSTR_LITERAL)
+      total_literal += delta->instructions[i].literal.length;
+    else
+      match_count++;
+  }
+  EXPECT_TRUE(match_count > 0);
+  EXPECT_TRUE(delta->delta_size < new_size / 2);
+
+  void *result = delta_apply(old_data, old_size, delta, block_size);
+  EXPECT_TRUE(result != NULL);
+  EXPECT_TRUE(delta->new_file_size == new_size);
+  EXPECT_TRUE(memcmp(result, new_data, (size_t)new_size) == 0);
+
+  free(result);
+  delta_destroy(delta);
+  delta_signature_destroy(sig);
+  free(old_data);
+  free(new_data);
+}
+
 void test_delta() {
   test_adler32_basic();
   test_adler32_different_data();
@@ -280,4 +330,5 @@ void test_delta() {
   test_delta_file_shrink();
   test_should_attempt();
   test_is_worthwhile();
+  test_large_file_delta();
 }