diff --git a/deltachat-ffi/src/lib.rs b/deltachat-ffi/src/lib.rs
index 30d1cb17e..c0cfd82e9 100644
--- a/deltachat-ffi/src/lib.rs
+++ b/deltachat-ffi/src/lib.rs
@@ -684,7 +684,11 @@ pub unsafe extern "C" fn dc_get_msg<'a>(
 
 #[no_mangle]
 pub unsafe extern "C" fn dc_may_be_valid_addr(addr: *mut libc::c_char) -> libc::c_int {
-    dc_contact::dc_may_be_valid_addr(addr)
+    if dc_contact::dc_may_be_valid_addr(addr) {
+        1
+    } else {
+        0
+    }
 }
 
 #[no_mangle]
@@ -782,7 +786,11 @@ pub unsafe extern "C" fn dc_delete_contact(
     assert!(!context.is_null());
     let context = &*context;
 
-    dc_contact::dc_delete_contact(context, contact_id)
+    if dc_contact::dc_delete_contact(context, contact_id) {
+        1
+    } else {
+        0
+    }
 }
 
 #[no_mangle]
@@ -1052,7 +1060,11 @@ pub unsafe extern "C" fn dc_array_search_id(
     needle: libc::c_uint,
     ret_index: *mut libc::size_t,
 ) -> libc::c_int {
-    dc_array::dc_array_search_id(array, needle, ret_index)
+    if dc_array::dc_array_search_id(array, needle, ret_index) {
+        1
+    } else {
+        0
+    }
 }
 #[no_mangle]
 pub unsafe extern "C" fn dc_array_get_raw(array: *const dc_array_t) -> *const libc::size_t {
@@ -1289,7 +1301,11 @@ pub unsafe extern "C" fn dc_msg_get_height(msg: *mut dc_msg::dc_msg_t) -> libc::
 
 #[no_mangle]
 pub unsafe extern "C" fn dc_msg_get_duration(msg: *mut dc_msg::dc_msg_t) -> libc::c_int {
-    dc_msg::dc_msg_get_duration(msg)
+    if dc_msg::dc_msg_get_duration(msg) {
+        1
+    } else {
+        0
+    }
 }
 
 #[no_mangle]
@@ -1320,7 +1336,11 @@ pub unsafe extern "C" fn dc_msg_has_deviating_timestamp(msg: *mut dc_msg::dc_msg
 
 #[no_mangle]
 pub unsafe extern "C" fn dc_msg_has_location(msg: *mut dc_msg::dc_msg_t) -> libc::c_int {
-    dc_msg::dc_msg_has_location(msg)
+    if dc_msg::dc_msg_has_location(msg) {
+        1
+    } else {
+        0
+    }
 }
 
 #[no_mangle]
diff --git a/examples/repl/cmdline.rs b/examples/repl/cmdline.rs
index 53bd3dc31..2b5f74c72 100644
--- a/examples/repl/cmdline.rs
+++ b/examples/repl/cmdline.rs
@@ -336,7 +336,7 @@ unsafe fn log_msg(context: &dc_context_t, prefix: *const libc::c_char, msg: *mut
         } else {
             b"\x00" as *const u8 as *const libc::c_char
         },
-        if 0 != dc_msg_has_location(msg) {
+        if dc_msg_has_location(msg) {
             b"\xf0\x9f\x93\x8d\x00" as *const u8 as *const libc::c_char
         } else {
             b"\x00" as *const u8 as *const libc::c_char
@@ -408,7 +408,7 @@ unsafe fn log_msglist(context: &dc_context_t, msglist: *mut dc_array_t) {
 unsafe fn log_contactlist(context: &dc_context_t, contacts: *mut dc_array_t) {
     let mut contact: *mut dc_contact_t;
     let peerstate: *mut dc_apeerstate_t = dc_apeerstate_new(context);
-    if 0 == dc_array_search_id(contacts, 1i32 as uint32_t, 0 as *mut size_t) {
+    if !dc_array_search_id(contacts, 1i32 as uint32_t, 0 as *mut size_t) {
         dc_array_add_id(contacts, 1i32 as uint32_t);
     }
     let mut i = 0;
@@ -1556,7 +1556,7 @@ pub unsafe fn dc_cmdline(context: &dc_context_t, cmdline: &str) -> *mut libc::c_
         }
     } else if strcmp(cmd, b"delcontact\x00" as *const u8 as *const libc::c_char) == 0i32 {
         if !arg1.is_empty() {
-            ret = if 0 != dc_delete_contact(context, arg1.parse().unwrap()) {
+            ret = if dc_delete_contact(context, arg1.parse().unwrap()) {
                 2i32 as *mut libc::c_char
             } else {
                 1i32 as *mut libc::c_char
diff --git a/src/dc_aheader.rs b/src/dc_aheader.rs
index 6f76073f2..c9b0ebdcb 100644
--- a/src/dc_aheader.rs
+++ b/src/dc_aheader.rs
@@ -194,7 +194,7 @@ unsafe fn add_attribute(
     value: *const libc::c_char,
 ) -> libc::c_int {
     if strcasecmp(name, b"addr\x00" as *const u8 as *const libc::c_char) == 0 {
-        if value.is_null() || 0 == dc_may_be_valid_addr(value) || !(*aheader).addr.is_null() {
+        if value.is_null() || !dc_may_be_valid_addr(value) || !(*aheader).addr.is_null() {
             return 0;
         }
         (*aheader).addr = dc_addr_normalize(value);
diff --git a/src/dc_array.rs b/src/dc_array.rs
index f8ecf90a2..79323b991 100644
--- a/src/dc_array.rs
+++ b/src/dc_array.rs
@@ -229,14 +229,13 @@ pub unsafe fn dc_array_is_independent(array: *const dc_array_t, index: size_t) -
     (*(*(*array).array.offset(index as isize) as *mut _dc_location)).independent as libc::c_int
 }
 
-// TODO should return bool /rtn
 pub unsafe fn dc_array_search_id(
     array: *const dc_array_t,
     needle: uint32_t,
     ret_index: *mut size_t,
-) -> libc::c_int {
+) -> bool {
     if array.is_null() || (*array).magic != 0xa11aai32 as libc::c_uint {
-        return 0i32;
+        return false;
     }
     let data: *mut uintptr_t = (*array).array;
     let mut i: size_t = 0;
@@ -246,11 +245,11 @@ pub unsafe fn dc_array_search_id(
             if !ret_index.is_null() {
                 *ret_index = i
             }
-            return 1i32;
+            return true;
         }
         i = i.wrapping_add(1)
     }
-    0
+    false
 }
 
 pub unsafe fn dc_array_get_raw(array: *const dc_array_t) -> *const uintptr_t {
diff --git a/src/dc_chat.rs b/src/dc_chat.rs
index e51340a8f..a62ef41e0 100644
--- a/src/dc_chat.rs
+++ b/src/dc_chat.rs
@@ -37,8 +37,8 @@ pub unsafe fn dc_create_chat_by_msg_id(context: &dc_context_t, msg_id: uint32_t)
     let mut send_event: libc::c_int = 0i32;
     let msg: *mut dc_msg_t = dc_msg_new_untyped(context);
     let chat: *mut dc_chat_t = dc_chat_new(context);
-    if !(0 == dc_msg_load_from_db(msg, context, msg_id)
-        || 0 == dc_chat_load_from_db(chat, (*msg).chat_id)
+    if !(!dc_msg_load_from_db(msg, context, msg_id)
+        || !dc_chat_load_from_db(chat, (*msg).chat_id)
         || (*chat).id <= 9i32 as libc::c_uint)
     {
         chat_id = (*chat).id;
@@ -129,9 +129,8 @@ pub unsafe fn dc_block_chat(context: &dc_context_t, chat_id: uint32_t, new_block
     sqlite3_finalize(stmt);
 }
 
-// TODO should return bool /rtn
-pub unsafe fn dc_chat_load_from_db(chat: *mut dc_chat_t, chat_id: uint32_t) -> libc::c_int {
-    let mut success: libc::c_int = 0i32;
+pub unsafe fn dc_chat_load_from_db(chat: *mut dc_chat_t, chat_id: uint32_t) -> bool {
+    let mut success = false;
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
     if !(chat.is_null() || (*chat).magic != 0xc4a7c4a7u32) {
         dc_chat_empty(chat);
@@ -146,7 +145,7 @@ pub unsafe fn dc_chat_load_from_db(chat: *mut dc_chat_t, chat_id: uint32_t) -> l
 
         if !(sqlite3_step(stmt) != 100i32) {
             if !(0 == set_from_stmt(chat, stmt)) {
-                success = 1i32
+                success = true
             }
         }
     }
@@ -227,9 +226,7 @@ pub unsafe fn dc_create_chat_by_contact_id(
             dc_unblock_chat(context, chat_id);
             send_event = 1i32
         }
-    } else if 0i32 == dc_real_contact_exists(context, contact_id)
-        && contact_id != 1i32 as libc::c_uint
-    {
+    } else if !dc_real_contact_exists(context, contact_id) && contact_id != 1i32 as libc::c_uint {
         dc_log_warning(
             context,
             0i32,
@@ -297,7 +294,7 @@ pub unsafe fn dc_create_or_lookup_nchat_by_contact_id(
         return;
     }
     contact = dc_contact_new(context);
-    if !(0 == dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id)) {
+    if dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id) {
         chat_name =
             if !(*contact).name.is_null() && 0 != *(*contact).name.offset(0isize) as libc::c_int {
                 (*contact).name
@@ -518,7 +515,7 @@ unsafe fn prepare_msg_common<'a>(
         17281240262373992796 => {
             dc_unarchive_chat(context, chat_id);
             chat = dc_chat_new(context);
-            if 0 != dc_chat_load_from_db(chat, chat_id) {
+            if dc_chat_load_from_db(chat, chat_id) {
                 if (*msg).state != 18i32 {
                     (*msg).state = 20i32
                 }
@@ -1209,7 +1206,7 @@ pub unsafe fn dc_get_draft(context: &dc_context_t, chat_id: uint32_t) -> *mut dc
         return 0 as *mut dc_msg_t;
     }
     draft_msg = dc_msg_new_untyped(context);
-    if 0 == dc_msg_load_from_db(draft_msg, context, draft_msg_id) {
+    if !dc_msg_load_from_db(draft_msg, context, draft_msg_id) {
         dc_msg_unref(draft_msg);
         return 0 as *mut dc_msg_t;
     }
@@ -1436,7 +1433,7 @@ pub unsafe fn dc_get_next_media(
     let mut i: libc::c_int;
     let cnt: libc::c_int;
 
-    if !(0 == dc_msg_load_from_db(msg, context, curr_msg_id)) {
+    if dc_msg_load_from_db(msg, context, curr_msg_id) {
         list = dc_get_chat_media(
             context,
             (*msg).chat_id,
@@ -1512,7 +1509,7 @@ pub unsafe fn dc_delete_chat(context: &dc_context_t, chat_id: uint32_t) {
     let obj: *mut dc_chat_t = dc_chat_new(context);
     let mut q3: *mut libc::c_char = 0 as *mut libc::c_char;
     if !(chat_id <= 9i32 as libc::c_uint) {
-        if !(0 == dc_chat_load_from_db(obj, chat_id)) {
+        if !(!dc_chat_load_from_db(obj, chat_id)) {
             q3 = sqlite3_mprintf(
                 b"DELETE FROM msgs_mdns WHERE msg_id IN (SELECT id FROM msgs WHERE chat_id=%i);\x00"
                     as *const u8 as *const libc::c_char,
@@ -1593,7 +1590,7 @@ pub unsafe fn dc_get_chat(context: &dc_context_t, chat_id: uint32_t) -> *mut dc_
     let mut success: libc::c_int = 0i32;
     let obj: *mut dc_chat_t = dc_chat_new(context);
 
-    if !(0 == dc_chat_load_from_db(obj, chat_id)) {
+    if !(!dc_chat_load_from_db(obj, chat_id)) {
         success = 1i32
     }
 
@@ -1714,9 +1711,8 @@ pub unsafe fn dc_add_contact_to_chat_ex(
         dc_reset_gossiped_timestamp(context, chat_id);
         /*this also makes sure, not contacts are added to special or normal chats*/
         if !(0i32 == real_group_exists(context, chat_id)
-            || 0i32 == dc_real_contact_exists(context, contact_id)
-                && contact_id != 1i32 as libc::c_uint
-            || 0i32 == dc_chat_load_from_db(chat, chat_id))
+            || !dc_real_contact_exists(context, contact_id) && contact_id != 1i32 as libc::c_uint
+            || !dc_chat_load_from_db(chat, chat_id))
         {
             if !(dc_is_contact_in_chat(context, chat_id, 1i32 as uint32_t) == 1i32) {
                 dc_log_event(
@@ -1902,9 +1898,7 @@ pub unsafe fn dc_remove_contact_from_chat(
     {
         /* we do not check if "contact_id" exists but just delete all records with the id from chats_contacts */
         /* this allows to delete pending references to deleted contacts.  Of course, this should _not_ happen. */
-        if !(0i32 == real_group_exists(context, chat_id)
-            || 0i32 == dc_chat_load_from_db(chat, chat_id))
-        {
+        if !(0i32 == real_group_exists(context, chat_id) || !dc_chat_load_from_db(chat, chat_id)) {
             if !(dc_is_contact_in_chat(context, chat_id, 1i32 as uint32_t) == 1i32) {
                 dc_log_event(
                     context,
@@ -2017,9 +2011,7 @@ pub unsafe fn dc_set_chat_name(
         || *new_name.offset(0isize) as libc::c_int == 0i32
         || chat_id <= 9i32 as libc::c_uint)
     {
-        if !(0i32 == real_group_exists(context, chat_id)
-            || 0i32 == dc_chat_load_from_db(chat, chat_id))
-        {
+        if !(0i32 == real_group_exists(context, chat_id) || !dc_chat_load_from_db(chat, chat_id)) {
             if strcmp((*chat).name, new_name) == 0i32 {
                 success = 1i32
             } else if !(dc_is_contact_in_chat(context, chat_id, 1i32 as uint32_t) == 1i32) {
@@ -2089,9 +2081,7 @@ pub unsafe fn dc_set_chat_profile_image(
     let mut msg: *mut dc_msg_t = dc_msg_new_untyped(context);
     let mut new_image_rel: *mut libc::c_char = 0 as *mut libc::c_char;
     if !(chat_id <= 9i32 as libc::c_uint) {
-        if !(0i32 == real_group_exists(context, chat_id)
-            || 0i32 == dc_chat_load_from_db(chat, chat_id))
-        {
+        if !(0i32 == real_group_exists(context, chat_id) || !dc_chat_load_from_db(chat, chat_id)) {
             if !(dc_is_contact_in_chat(context, chat_id, 1i32 as uint32_t) == 1i32) {
                 dc_log_event(
                     context,
@@ -2178,7 +2168,7 @@ pub unsafe fn dc_forward_msgs(
     let original_param: *mut dc_param_t = dc_param_new();
     if !(msg_ids.is_null() || msg_cnt <= 0i32 || chat_id <= 9i32 as libc::c_uint) {
         dc_unarchive_chat(context, chat_id);
-        if !(0 == dc_chat_load_from_db(chat, chat_id)) {
+        if !(!dc_chat_load_from_db(chat, chat_id)) {
             curr_timestamp = dc_create_smeared_timestamps(context, msg_cnt);
             idsstr = dc_arr_to_string(msg_ids, msg_cnt);
             q3 = sqlite3_mprintf(
@@ -2192,7 +2182,7 @@ pub unsafe fn dc_forward_msgs(
                     break;
                 }
                 let src_msg_id: libc::c_int = sqlite3_column_int(stmt, 0i32);
-                if 0 == dc_msg_load_from_db(msg, context, src_msg_id as uint32_t) {
+                if !dc_msg_load_from_db(msg, context, src_msg_id as uint32_t) {
                     break;
                 }
                 dc_param_set_packed(original_param, (*(*msg).param).packed);
diff --git a/src/dc_chatlist.rs b/src/dc_chatlist.rs
index 4f89e7ce3..b1761e885 100644
--- a/src/dc_chatlist.rs
+++ b/src/dc_chatlist.rs
@@ -324,7 +324,7 @@ pub unsafe fn dc_chatlist_get_summary<'a>(
         if chat.is_null() {
             chat = dc_chat_new((*chatlist).context);
             chat_to_delete = chat;
-            if 0 == dc_chat_load_from_db(
+            if !dc_chat_load_from_db(
                 chat,
                 dc_array_get_id((*chatlist).chatNlastmsg_ids, index.wrapping_mul(2)),
             ) {
diff --git a/src/dc_contact.rs b/src/dc_contact.rs
index 536546444..f5e4aa169 100644
--- a/src/dc_contact.rs
+++ b/src/dc_contact.rs
@@ -46,14 +46,13 @@ pub unsafe fn dc_marknoticed_contact(context: &dc_context_t, contact_id: uint32_
 }
 
 // handle contacts
-// TODO should return bool /rtn
-pub unsafe extern "C" fn dc_may_be_valid_addr(addr: *const libc::c_char) -> libc::c_int {
+pub unsafe extern "C" fn dc_may_be_valid_addr(addr: *const libc::c_char) -> bool {
     if addr.is_null() {
-        return 0i32;
+        return false;
     }
     let at: *const libc::c_char = strchr(addr, '@' as i32);
     if at.is_null() || (at.wrapping_offset_from(addr) as libc::c_long) < 1i32 as libc::c_long {
-        return 0i32;
+        return false;
     }
     let dot: *const libc::c_char = strchr(at, '.' as i32);
     if dot.is_null()
@@ -61,10 +60,10 @@ pub unsafe extern "C" fn dc_may_be_valid_addr(addr: *const libc::c_char) -> libc
         || *dot.offset(1isize) as libc::c_int == 0i32
         || *dot.offset(2isize) as libc::c_int == 0i32
     {
-        return 0i32;
+        return false;
     }
 
-    1
+    true
 }
 
 pub unsafe fn dc_lookup_contact_id_by_addr(
@@ -137,7 +136,7 @@ pub unsafe fn dc_create_contact(
 ) -> uint32_t {
     let mut contact_id: uint32_t = 0i32 as uint32_t;
     let mut sth_modified: libc::c_int = 0i32;
-    let blocked: libc::c_int;
+    let blocked: bool;
     if !(addr.is_null() || *addr.offset(0isize) as libc::c_int == 0i32) {
         contact_id = dc_add_or_lookup_contact(context, name, addr, 0x4000000i32, &mut sth_modified);
         blocked = dc_is_contact_blocked(context, contact_id);
@@ -151,7 +150,7 @@ pub unsafe fn dc_create_contact(
             }) as uintptr_t,
             0i32 as uintptr_t,
         );
-        if 0 != blocked {
+        if blocked {
             dc_block_contact(context, contact_id, 0i32);
         }
     }
@@ -169,7 +168,7 @@ pub unsafe fn dc_block_contact(
     let contact: *mut dc_contact_t = dc_contact_new(context);
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
     if !(contact_id <= 9i32 as libc::c_uint) {
-        if 0 != dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id)
+        if dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id)
             && (*contact).blocked != new_blocking
         {
             stmt = dc_sqlite3_prepare(
@@ -296,14 +295,13 @@ pub unsafe fn dc_contact_empty(mut contact: *mut dc_contact_t) {
 /* contacts with at least this origin value are shown in the contact list */
 /* contacts with at least this origin value are verified and known not to be spam */
 /* contacts with at least this origin value start a new "normal" chat, defaults to off */
-// TODO should return bool /rtn
 pub unsafe fn dc_contact_load_from_db(
     contact: *mut dc_contact_t,
     sql: &dc_sqlite3_t,
     contact_id: uint32_t,
-) -> libc::c_int {
+) -> bool {
     let current_block: u64;
-    let mut success: libc::c_int = 0i32;
+    let mut success = false;
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
     if !(contact.is_null() || (*contact).magic != 0xc047ac7i32 as libc::c_uint) {
         dc_contact_empty(contact);
@@ -339,7 +337,7 @@ pub unsafe fn dc_contact_load_from_db(
         }
         match current_block {
             12908855840294526070 => {}
-            _ => success = 1i32,
+            _ => success = true,
         }
     }
     sqlite3_finalize(stmt);
@@ -347,13 +345,12 @@ pub unsafe fn dc_contact_load_from_db(
     success
 }
 
-// TODO should return bool /rtn
-pub unsafe fn dc_is_contact_blocked(context: &dc_context_t, contact_id: uint32_t) -> libc::c_int {
-    let mut is_blocked: libc::c_int = 0i32;
+pub unsafe fn dc_is_contact_blocked(context: &dc_context_t, contact_id: uint32_t) -> bool {
+    let mut is_blocked = false;
     let contact: *mut dc_contact_t = dc_contact_new(context);
-    if 0 != dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id) {
+    if dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id) {
         if 0 != (*contact).blocked {
-            is_blocked = 1i32
+            is_blocked = true
         }
     }
     dc_contact_unref(contact);
@@ -391,7 +388,7 @@ pub unsafe fn dc_add_or_lookup_contact(
         );
         if strcasecmp(addr, addr_self) == 0i32 {
             row_id = 1i32 as uint32_t
-        } else if 0 == dc_may_be_valid_addr(addr) {
+        } else if !dc_may_be_valid_addr(addr) {
             dc_log_warning(
                 context,
                 0i32,
@@ -786,7 +783,7 @@ pub unsafe fn dc_get_contact_encrinfo(
         eos: 0 as *mut libc::c_char,
     };
     dc_strbuilder_init(&mut ret, 0i32);
-    if !(0 == dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id)) {
+    if !(!dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id)) {
         dc_apeerstate_load_by_addr(
             peerstate,
             &context.sql.clone().read().unwrap(),
@@ -920,9 +917,8 @@ unsafe fn cat_fingerprint(
     };
 }
 
-// TODO should return bool /rtn
-pub unsafe fn dc_delete_contact(context: &dc_context_t, contact_id: uint32_t) -> libc::c_int {
-    let mut success: libc::c_int = 0i32;
+pub unsafe fn dc_delete_contact(context: &dc_context_t, contact_id: uint32_t) -> bool {
+    let mut success = false;
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
     if !contact_id <= 9i32 as libc::c_uint {
         stmt = dc_sqlite3_prepare(
@@ -957,7 +953,7 @@ pub unsafe fn dc_delete_contact(context: &dc_context_t, contact_id: uint32_t) ->
                         0i32 as uintptr_t,
                         0i32 as uintptr_t,
                     );
-                    success = 1i32
+                    success = true
                 }
             }
         }
@@ -969,7 +965,7 @@ pub unsafe fn dc_delete_contact(context: &dc_context_t, contact_id: uint32_t) ->
 
 pub unsafe fn dc_get_contact(context: &dc_context_t, contact_id: uint32_t) -> *mut dc_contact_t {
     let mut ret: *mut dc_contact_t = dc_contact_new(context);
-    if 0 == dc_contact_load_from_db(ret, &context.sql.clone().read().unwrap(), contact_id) {
+    if !dc_contact_load_from_db(ret, &context.sql.clone().read().unwrap(), contact_id) {
         dc_contact_unref(ret);
         ret = 0 as *mut dc_contact_t
     }
@@ -1163,20 +1159,19 @@ pub unsafe fn dc_addr_equals_self(
     ret
 }
 
-// TODO should return bool /rtn
 pub unsafe fn dc_addr_equals_contact(
     context: &dc_context_t,
     addr: *const libc::c_char,
     contact_id: uint32_t,
-) -> libc::c_int {
-    let mut addr_are_equal: libc::c_int = 0i32;
+) -> bool {
+    let mut addr_are_equal = false;
     if !addr.is_null() {
         let contact: *mut dc_contact_t = dc_contact_new(context);
-        if 0 != dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id) {
+        if dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id) {
             if !(*contact).addr.is_null() {
                 let normalized_addr: *mut libc::c_char = dc_addr_normalize(addr);
                 if strcasecmp((*contact).addr, normalized_addr) == 0i32 {
-                    addr_are_equal = 1i32
+                    addr_are_equal = true;
                 }
                 free(normalized_addr as *mut libc::c_void);
             }
@@ -1217,7 +1212,7 @@ pub unsafe fn dc_get_contact_origin(
     }
     let contact: *mut dc_contact_t = dc_contact_new(context);
     *ret_blocked = 0i32;
-    if !(0 == dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id)) {
+    if dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), contact_id) {
         /* we could optimize this by loading only the needed fields */
         if 0 != (*contact).blocked {
             *ret_blocked = 1i32
@@ -1229,10 +1224,9 @@ pub unsafe fn dc_get_contact_origin(
     ret
 }
 
-// TODO should return bool /rtn
-pub unsafe fn dc_real_contact_exists(context: &dc_context_t, contact_id: uint32_t) -> libc::c_int {
+pub unsafe fn dc_real_contact_exists(context: &dc_context_t, contact_id: uint32_t) -> bool {
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
-    let mut ret: libc::c_int = 0i32;
+    let mut ret = false;
     if !(context.sql.clone().read().unwrap().cobj.is_null() || contact_id <= 9i32 as libc::c_uint) {
         stmt = dc_sqlite3_prepare(
             context,
@@ -1241,7 +1235,7 @@ pub unsafe fn dc_real_contact_exists(context: &dc_context_t, contact_id: uint32_
         );
         sqlite3_bind_int(stmt, 1i32, contact_id as libc::c_int);
         if sqlite3_step(stmt) == 100i32 {
-            ret = 1i32
+            ret = true
         }
     }
     sqlite3_finalize(stmt);
diff --git a/src/dc_job.rs b/src/dc_job.rs
index aafcbd549..854e881e2 100644
--- a/src/dc_job.rs
+++ b/src/dc_job.rs
@@ -472,7 +472,7 @@ unsafe fn dc_job_do_DC_JOB_MOVE_MSG(context: &dc_context_t, job: &mut dc_job_t)
     }
     match current_block {
         2473556513754201174 => {
-            if !(0 == dc_msg_load_from_db(msg, context, job.foreign_id)) {
+            if dc_msg_load_from_db(msg, context, job.foreign_id) {
                 if dc_sqlite3_get_config_int(
                     context,
                     &context.sql.clone().read().unwrap(),
@@ -625,7 +625,7 @@ unsafe fn dc_job_do_DC_JOB_MARKSEEN_MSG_ON_IMAP(context: &dc_context_t, job: &mu
     }
     match current_block {
         15240798224410183470 => {
-            if !(0 == dc_msg_load_from_db(msg, context, job.foreign_id)) {
+            if dc_msg_load_from_db(msg, context, job.foreign_id) {
                 let server_folder = CStr::from_ptr((*msg).server_folder).to_str().unwrap();
                 match inbox.set_seen(context, server_folder, (*msg).server_uid) as libc::c_uint {
                     0 => {}
@@ -938,7 +938,7 @@ unsafe fn dc_job_do_DC_JOB_DELETE_MSG_ON_IMAP(context: &dc_context_t, job: &mut
     let msg: *mut dc_msg_t = dc_msg_new_untyped(context);
     let inbox = context.inbox.read().unwrap();
 
-    if !(0 == dc_msg_load_from_db(msg, context, job.foreign_id)
+    if !(!dc_msg_load_from_db(msg, context, job.foreign_id)
         || (*msg).rfc724_mid.is_null()
         || *(*msg).rfc724_mid.offset(0isize) as libc::c_int == 0i32)
     {
diff --git a/src/dc_mimefactory.rs b/src/dc_mimefactory.rs
index 836d9a786..af294d185 100644
--- a/src/dc_mimefactory.rs
+++ b/src/dc_mimefactory.rs
@@ -123,8 +123,8 @@ pub unsafe fn dc_mimefactory_load_msg(
         (*factory).recipients_addr = clist_new();
         (*factory).msg = dc_msg_new_untyped(context);
         (*factory).chat = dc_chat_new(context);
-        if 0 != dc_msg_load_from_db((*factory).msg, context, msg_id)
-            && 0 != dc_chat_load_from_db((*factory).chat, (*(*factory).msg).chat_id)
+        if dc_msg_load_from_db((*factory).msg, context, msg_id)
+            && dc_chat_load_from_db((*factory).chat, (*(*factory).msg).chat_id)
         {
             load_from(factory);
             (*factory).req_mdn = 0i32;
@@ -289,8 +289,8 @@ pub unsafe fn dc_mimefactory_load_mdn(
         {
             /* MDNs not enabled - check this is late, in the job. the use may have changed its choice while offline ... */
             contact = dc_contact_new((*factory).context);
-            if !(0 == dc_msg_load_from_db((*factory).msg, (*factory).context, msg_id)
-                || 0 == dc_contact_load_from_db(
+            if !(!dc_msg_load_from_db((*factory).msg, (*factory).context, msg_id)
+                || !dc_contact_load_from_db(
                     contact,
                     &mut (*factory).context.sql.clone().read().unwrap(),
                     (*(*factory).msg).from_id,
@@ -1131,7 +1131,7 @@ unsafe fn build_body_file(
     mut base_name: *const libc::c_char,
     ret_file_name_as_sent: *mut *mut libc::c_char,
 ) -> *mut mailmime {
-    let needs_ext: libc::c_int;
+    let needs_ext: bool;
     let mime_fields: *mut mailmime_fields;
     let mut mime_sub: *mut mailmime = 0 as *mut mailmime;
     let content: *mut mailmime_content;
@@ -1229,14 +1229,14 @@ unsafe fn build_body_file(
             needs_ext = dc_needs_ext_header(filename_to_send);
             mime_fields = mailmime_fields_new_filename(
                 MAILMIME_DISPOSITION_TYPE_ATTACHMENT as libc::c_int,
-                if 0 != needs_ext {
+                if needs_ext {
                     0 as *mut libc::c_char
                 } else {
                     dc_strdup(filename_to_send)
                 },
                 MAILMIME_MECHANISM_BASE64 as libc::c_int,
             );
-            if 0 != needs_ext {
+            if needs_ext {
                 let mut cur1: *mut clistiter = (*(*mime_fields).fld_list).first;
                 while !cur1.is_null() {
                     let field: *mut mailmime_field = (if !cur1.is_null() {
diff --git a/src/dc_msg.rs b/src/dc_msg.rs
index 7ad05d233..6e03e9b88 100644
--- a/src/dc_msg.rs
+++ b/src/dc_msg.rs
@@ -160,7 +160,7 @@ pub unsafe fn dc_get_msg_info(context: &dc_context_t, msg_id: uint32_t) -> *mut
                 p,
             );
             free(p as *mut libc::c_void);
-            if 0 != dc_msg_has_location(msg) {
+            if dc_msg_has_location(msg) {
                 dc_strbuilder_cat(
                     &mut ret,
                     b", Location sent\x00" as *const u8 as *const libc::c_char,
@@ -448,13 +448,12 @@ pub unsafe fn dc_msg_get_file(msg: *const dc_msg_t) -> *mut libc::c_char {
  * @param msg The message object.
  * @return 1=Message has location bound to it, 0=No location bound to message.
  */
-// TODO should return bool /rtn
-pub unsafe fn dc_msg_has_location(msg: *const dc_msg_t) -> libc::c_int {
+pub unsafe fn dc_msg_has_location(msg: *const dc_msg_t) -> bool {
     if msg.is_null() || (*msg).magic != 0x11561156i32 as libc::c_uint {
-        return 0i32;
+        return false;
     }
 
-    ((*msg).location_id != 0i32 as libc::c_uint) as libc::c_int
+    ((*msg).location_id != 0i32 as libc::c_uint)
 }
 
 /**
@@ -505,13 +504,12 @@ pub unsafe fn dc_msg_get_timestamp(msg: *const dc_msg_t) -> time_t {
     };
 }
 
-// TODO should return bool /rtn
 pub unsafe fn dc_msg_load_from_db<'a>(
     msg: *mut dc_msg_t<'a>,
     context: &'a dc_context_t,
     id: uint32_t,
-) -> libc::c_int {
-    let mut success: libc::c_int = 0i32;
+) -> bool {
+    let mut success = false;
     let mut stmt = 0 as *mut sqlite3_stmt;
     if !msg.is_null() {
         stmt =
@@ -525,7 +523,7 @@ pub unsafe fn dc_msg_load_from_db<'a>(
             if !(0 == dc_msg_set_from_stmt(msg, stmt, 0i32)) {
                 /* also calls dc_msg_empty() */
                 (*msg).context = context;
-                success = 1i32
+                success = true
             }
         }
     }
@@ -777,7 +775,7 @@ pub unsafe fn dc_star_msgs(
 pub unsafe fn dc_get_msg<'a>(context: &'a dc_context_t, msg_id: uint32_t) -> *mut dc_msg_t<'a> {
     let mut success: libc::c_int = 0i32;
     let obj: *mut dc_msg_t = dc_msg_new_untyped(context);
-    if !(0 == dc_msg_load_from_db(obj, context, msg_id)) {
+    if dc_msg_load_from_db(obj, context, msg_id) {
         success = 1i32
     }
     if 0 != success {
@@ -905,13 +903,12 @@ pub unsafe fn dc_msg_get_height(msg: *const dc_msg_t) -> libc::c_int {
     dc_param_get_int((*msg).param, 'h' as i32, 0i32)
 }
 
-// TODO should return bool /rtn
-pub unsafe fn dc_msg_get_duration(msg: *const dc_msg_t) -> libc::c_int {
+pub unsafe fn dc_msg_get_duration(msg: *const dc_msg_t) -> bool {
     if msg.is_null() || (*msg).magic != 0x11561156i32 as libc::c_uint {
-        return 0i32;
+        return false;
     }
 
-    dc_param_get_int((*msg).param, 'd' as i32, 0i32)
+    0 != dc_param_get_int((*msg).param, 'd' as i32, 0i32)
 }
 
 // TODO should return bool /rtn
@@ -1267,7 +1264,7 @@ pub unsafe fn dc_msg_new_load<'a>(
 pub unsafe fn dc_delete_msg_from_db(context: &dc_context_t, msg_id: uint32_t) {
     let msg: *mut dc_msg_t = dc_msg_new_untyped(context);
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
-    if !(0 == dc_msg_load_from_db(msg, context, msg_id)) {
+    if dc_msg_load_from_db(msg, context, msg_id) {
         stmt = dc_sqlite3_prepare(
             context,
             &context.sql.clone().read().unwrap(),
@@ -1346,7 +1343,7 @@ pub unsafe fn dc_set_msg_failed(
 ) {
     let mut msg = dc_msg_new_untyped(context);
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
-    if !(0 == dc_msg_load_from_db(msg, context, msg_id)) {
+    if dc_msg_load_from_db(msg, context, msg_id) {
         if 18i32 == (*msg).state || 20i32 == (*msg).state || 26i32 == (*msg).state {
             (*msg).state = 24i32
         }
diff --git a/src/dc_oauth2.rs b/src/dc_oauth2.rs
index 1e34bf994..7ed5f0294 100644
--- a/src/dc_oauth2.rs
+++ b/src/dc_oauth2.rs
@@ -173,7 +173,7 @@ pub unsafe fn dc_get_oauth2_access_token(
 
             let l = lock.lock().unwrap();
             // read generated token
-            if 0 == flags & 0x1i32 && 0 == is_expired(context) {
+            if 0 == flags & 0x1i32 && !is_expired(context) {
                 access_token = dc_sqlite3_get_config(
                     context,
                     &context.sql.clone().read().unwrap(),
@@ -488,8 +488,7 @@ unsafe extern "C" fn jsoneq(
     -1
 }
 
-// TODO should return bool /rtn
-unsafe fn is_expired(context: &dc_context_t) -> libc::c_int {
+unsafe fn is_expired(context: &dc_context_t) -> bool {
     let expire_timestamp: time_t = dc_sqlite3_get_config_int64(
         context,
         &context.sql.clone().read().unwrap(),
@@ -497,13 +496,13 @@ unsafe fn is_expired(context: &dc_context_t) -> libc::c_int {
         0i32 as int64_t,
     ) as time_t;
     if expire_timestamp <= 0i32 as libc::c_long {
-        return 0i32;
+        return false;
     }
     if expire_timestamp > time(0 as *mut time_t) {
-        return 0i32;
+        return false;
     }
 
-    1
+    true
 }
 
 pub unsafe fn dc_get_oauth2_addr(
diff --git a/src/dc_qr.rs b/src/dc_qr.rs
index 520794a4a..ee447c006 100644
--- a/src/dc_qr.rs
+++ b/src/dc_qr.rs
@@ -205,7 +205,7 @@ pub unsafe fn dc_check_qr(context: &dc_context_t, qr: *const libc::c_char) -> *m
                     temp = dc_addr_normalize(addr);
                     free(addr as *mut libc::c_void);
                     addr = temp;
-                    if 0 == dc_may_be_valid_addr(addr) {
+                    if !dc_may_be_valid_addr(addr) {
                         (*qr_parsed).state = 400i32;
                         (*qr_parsed).text1 = dc_strdup(
                             b"Bad e-mail address.\x00" as *const u8 as *const libc::c_char,
diff --git a/src/dc_receive_imf.rs b/src/dc_receive_imf.rs
index 2bd82c03e..c31f68adf 100644
--- a/src/dc_receive_imf.rs
+++ b/src/dc_receive_imf.rs
@@ -408,7 +408,7 @@ pub unsafe fn dc_receive_imf(
                                     }
                                     if chat_id == 0i32 as libc::c_uint && 0 != allow_creation {
                                         let create_blocked_1: libc::c_int = if 0 != msgrmsg
-                                            && 0 == dc_is_contact_blocked(context, to_id)
+                                            && !dc_is_contact_blocked(context, to_id)
                                         {
                                             0i32
                                         } else {
@@ -1470,14 +1470,13 @@ unsafe fn create_or_lookup_group(
                                 dc_add_to_chat_contacts_table(context, chat_id, 1i32 as uint32_t);
                             }
                             if from_id > 9i32 {
-                                if dc_addr_equals_contact(context, self_addr, from_id as uint32_t)
-                                    == 0i32
+                                if !dc_addr_equals_contact(context, self_addr, from_id as uint32_t)
                                     && (skip.is_null()
-                                        || dc_addr_equals_contact(
+                                        || !dc_addr_equals_contact(
                                             context,
                                             skip,
                                             from_id as uint32_t,
-                                        ) == 0i32)
+                                        ))
                                 {
                                     dc_add_to_chat_contacts_table(
                                         context,
@@ -1489,9 +1488,9 @@ unsafe fn create_or_lookup_group(
                             i = 0i32;
                             while i < to_ids_cnt {
                                 let to_id: uint32_t = dc_array_get_id(to_ids, i as size_t);
-                                if dc_addr_equals_contact(context, self_addr, to_id) == 0i32
+                                if !dc_addr_equals_contact(context, self_addr, to_id)
                                     && (skip.is_null()
-                                        || dc_addr_equals_contact(context, skip, to_id) == 0i32)
+                                        || !dc_addr_equals_contact(context, skip, to_id))
                                 {
                                     dc_add_to_chat_contacts_table(context, chat_id, to_id);
                                 }
@@ -1576,10 +1575,10 @@ unsafe fn create_or_lookup_adhoc_group(
     if !(dc_array_get_cnt(to_ids) == 0 || 0 != dc_mimeparser_is_mailinglist_message(mime_parser)) {
         /* too few contacts or a mailinglist */
         member_ids = dc_array_duplicate(to_ids);
-        if 0 == dc_array_search_id(member_ids, from_id as uint32_t, 0 as *mut size_t) {
+        if !dc_array_search_id(member_ids, from_id as uint32_t, 0 as *mut size_t) {
             dc_array_add_id(member_ids, from_id as uint32_t);
         }
-        if 0 == dc_array_search_id(member_ids, 1i32 as uint32_t, 0 as *mut size_t) {
+        if !dc_array_search_id(member_ids, 1i32 as uint32_t, 0 as *mut size_t) {
             dc_array_add_id(member_ids, 1i32 as uint32_t);
         }
         if !(dc_array_get_cnt(member_ids) < 3) {
@@ -1803,7 +1802,7 @@ unsafe fn search_chat_ids_by_contact_ids(
         while i < iCnt {
             let curr_id: uint32_t = dc_array_get_id(unsorted_contact_ids, i as size_t);
             if curr_id != 1i32 as libc::c_uint
-                && 0 == dc_array_search_id(contact_ids, curr_id, 0 as *mut size_t)
+                && !dc_array_search_id(contact_ids, curr_id, 0 as *mut size_t)
             {
                 dc_array_add_id(contact_ids, curr_id);
             }
@@ -1866,7 +1865,7 @@ unsafe fn check_verified_properties(
     let mut to_ids_str: *mut libc::c_char = 0 as *mut libc::c_char;
     let mut q3: *mut libc::c_char = 0 as *mut libc::c_char;
     let mut stmt: *mut sqlite3_stmt = 0 as *mut sqlite3_stmt;
-    if 0 == dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), from_id) {
+    if !dc_contact_load_from_db(contact, &context.sql.clone().read().unwrap(), from_id) {
         *failure_reason = dc_mprintf(
             b"%s. See \"Info\" for details.\x00" as *const u8 as *const libc::c_char,
             b"Internal Error; cannot load contact.\x00" as *const u8 as *const libc::c_char,
@@ -2340,7 +2339,7 @@ unsafe fn add_or_lookup_contact_by_addr(
     );
     free(display_name_dec as *mut libc::c_void);
     if 0 != row_id {
-        if 0 == dc_array_search_id(ids, row_id, 0 as *mut size_t) {
+        if !dc_array_search_id(ids, row_id, 0 as *mut size_t) {
             dc_array_add_id(ids, row_id);
         }
     };
diff --git a/src/dc_securejoin.rs b/src/dc_securejoin.rs
index dd28440ee..3d60cc2c3 100644
--- a/src/dc_securejoin.rs
+++ b/src/dc_securejoin.rs
@@ -363,13 +363,12 @@ unsafe fn fingerprint_equals_sender(
     let peerstate: *mut dc_apeerstate_t = dc_apeerstate_new(context);
     let mut fingerprint_normalized: *mut libc::c_char = 0 as *mut libc::c_char;
     if !(dc_array_get_cnt(contacts) != 1) {
-        if !(0
-            == dc_contact_load_from_db(
-                contact,
-                &context.sql.clone().read().unwrap(),
-                dc_array_get_id(contacts, 0i32 as size_t),
-            )
-            || 0 == dc_apeerstate_load_by_addr(
+        if !(!dc_contact_load_from_db(
+            contact,
+            &context.sql.clone().read().unwrap(),
+            dc_array_get_id(contacts, 0i32 as size_t),
+        ) || 0
+            == dc_apeerstate_load_by_addr(
                 peerstate,
                 &context.sql.clone().read().unwrap(),
                 (*contact).addr,
diff --git a/src/dc_simplify.rs b/src/dc_simplify.rs
index e70b91f05..eb5de28b9 100644
--- a/src/dc_simplify.rs
+++ b/src/dc_simplify.rs
@@ -158,9 +158,9 @@ unsafe fn dc_simplify_simplify_plain_text(
         l = l_last;
         while l >= l_first {
             line = carray_get(lines, l as libc::c_uint) as *mut libc::c_char;
-            if 0 != is_plain_quote(line) {
+            if is_plain_quote(line) {
                 l_lastQuotedLine = l
-            } else if 0 == is_empty_line(line) {
+            } else if !is_empty_line(line) {
                 break;
             }
             l -= 1
@@ -169,14 +169,13 @@ unsafe fn dc_simplify_simplify_plain_text(
             l_last = l_lastQuotedLine - 1i32;
             (*simplify).is_cut_at_end = 1i32;
             if l_last > 0i32 {
-                if 0 != is_empty_line(carray_get(lines, l_last as libc::c_uint) as *mut libc::c_char)
-                {
+                if is_empty_line(carray_get(lines, l_last as libc::c_uint) as *mut libc::c_char) {
                     l_last -= 1
                 }
             }
             if l_last > 0i32 {
                 line = carray_get(lines, l_last as libc::c_uint) as *mut libc::c_char;
-                if 0 != is_quoted_headline(line) {
+                if is_quoted_headline(line) {
                     l_last -= 1
                 }
             }
@@ -188,12 +187,10 @@ unsafe fn dc_simplify_simplify_plain_text(
         l = l_first;
         while l <= l_last {
             line = carray_get(lines, l as libc::c_uint) as *mut libc::c_char;
-            if 0 != is_plain_quote(line) {
+            if is_plain_quote(line) {
                 l_lastQuotedLine_0 = l
-            } else if 0 == is_empty_line(line) {
-                if 0 != is_quoted_headline(line)
-                    && 0 == hasQuotedHeadline
-                    && l_lastQuotedLine_0 == -1i32
+            } else if !is_empty_line(line) {
+                if is_quoted_headline(line) && 0 == hasQuotedHeadline && l_lastQuotedLine_0 == -1i32
                 {
                     hasQuotedHeadline = 1i32
                 } else {
@@ -225,7 +222,7 @@ unsafe fn dc_simplify_simplify_plain_text(
     l = l_first;
     while l <= l_last {
         line = carray_get(lines, l as libc::c_uint) as *mut libc::c_char;
-        if 0 != is_empty_line(line) {
+        if is_empty_line(line) {
             pending_linebreaks += 1
         } else {
             if 0 != content_lines_added {
@@ -256,42 +253,39 @@ unsafe fn dc_simplify_simplify_plain_text(
 /* ******************************************************************************
  * Tools
  ******************************************************************************/
-// TODO should return bool /rtn
-unsafe fn is_empty_line(buf: *const libc::c_char) -> libc::c_int {
+unsafe fn is_empty_line(buf: *const libc::c_char) -> bool {
     /* force unsigned - otherwise the `> ' '` comparison will fail */
     let mut p1: *const libc::c_uchar = buf as *const libc::c_uchar;
     while 0 != *p1 {
         if *p1 as libc::c_int > ' ' as i32 {
-            return 0i32;
+            return false;
         }
         p1 = p1.offset(1isize)
     }
 
-    1
+    true
 }
 
-// TODO should return bool /rtn
-unsafe fn is_quoted_headline(buf: *const libc::c_char) -> libc::c_int {
+unsafe fn is_quoted_headline(buf: *const libc::c_char) -> bool {
     /* This function may be called for the line _directly_ before a quote.
     The function checks if the line contains sth. like "On 01.02.2016, xy@z wrote:" in various languages.
     - Currently, we simply check if the last character is a ':'.
     - Checking for the existance of an email address may fail (headlines may show the user's name instead of the address) */
     let buf_len: libc::c_int = strlen(buf) as libc::c_int;
     if buf_len > 80i32 {
-        return 0i32;
+        return false;
     }
     if buf_len > 0i32 && *buf.offset((buf_len - 1i32) as isize) as libc::c_int == ':' as i32 {
-        return 1i32;
+        return true;
     }
 
-    0
+    false
 }
 
-// TODO should return bool /rtn
-unsafe fn is_plain_quote(buf: *const libc::c_char) -> libc::c_int {
+unsafe fn is_plain_quote(buf: *const libc::c_char) -> bool {
     if *buf.offset(0isize) as libc::c_int == '>' as i32 {
-        return 1i32;
+        return true;
     }
 
-    0
+    false
 }
diff --git a/src/dc_strencode.rs b/src/dc_strencode.rs
index efd93129a..95a845fbb 100644
--- a/src/dc_strencode.rs
+++ b/src/dc_strencode.rs
@@ -145,15 +145,15 @@ pub unsafe fn dc_encode_header_words(to_encode: *const libc::c_char) -> *mut lib
                 if *cur as libc::c_int != '\u{0}' as i32 {
                     let begin: *const libc::c_char;
                     let mut end: *const libc::c_char;
-                    let mut do_quote: libc::c_int;
+                    let mut do_quote: bool;
                     let mut quote_words: libc::c_int;
                     begin = cur;
                     end = begin;
                     quote_words = 0i32;
-                    do_quote = 1i32;
+                    do_quote = true;
                     while *cur as libc::c_int != '\u{0}' as i32 {
                         get_word(cur, &mut cur, &mut do_quote);
-                        if !(0 != do_quote) {
+                        if !do_quote {
                             break;
                         }
                         quote_words = 1i32;
@@ -163,7 +163,7 @@ pub unsafe fn dc_encode_header_words(to_encode: *const libc::c_char) -> *mut lib
                         }
                     }
                     if 0 != quote_words {
-                        if 0 == quote_word(
+                        if !quote_word(
                             b"utf-8\x00" as *const u8 as *const libc::c_char,
                             mmapstr,
                             begin,
@@ -222,25 +222,24 @@ pub unsafe fn dc_encode_header_words(to_encode: *const libc::c_char) -> *mut lib
     ret_str
 }
 
-// TODO return bool /rtn
 unsafe fn quote_word(
     display_charset: *const libc::c_char,
     mmapstr: *mut MMAPString,
     word: *const libc::c_char,
     size: size_t,
-) -> libc::c_int {
+) -> bool {
     let mut cur: *const libc::c_char;
     let mut i: size_t = 0i32 as size_t;
     let mut hex: [libc::c_char; 4] = [0; 4];
     // let mut col: libc::c_int = 0i32;
     if mmap_string_append(mmapstr, b"=?\x00" as *const u8 as *const libc::c_char).is_null() {
-        return 0i32;
+        return false;
     }
     if mmap_string_append(mmapstr, display_charset).is_null() {
-        return 0i32;
+        return false;
     }
     if mmap_string_append(mmapstr, b"?Q?\x00" as *const u8 as *const libc::c_char).is_null() {
-        return 0i32;
+        return false;
     }
     // col = (*mmapstr).len as libc::c_int;
     cur = word;
@@ -263,16 +262,16 @@ unsafe fn quote_word(
                 *cur as libc::c_uchar as libc::c_int,
             );
             if mmap_string_append(mmapstr, hex.as_mut_ptr()).is_null() {
-                return 0i32;
+                return false;
             }
         // col += 3i32
         } else {
             if *cur as libc::c_int == ' ' as i32 {
                 if mmap_string_append_c(mmapstr, '_' as i32 as libc::c_char).is_null() {
-                    return 0i32;
+                    return false;
                 }
             } else if mmap_string_append_c(mmapstr, *cur).is_null() {
-                return 0i32;
+                return false;
             }
             // col += 3i32
         }
@@ -280,16 +279,16 @@ unsafe fn quote_word(
         i = i.wrapping_add(1)
     }
     if mmap_string_append(mmapstr, b"?=\x00" as *const u8 as *const libc::c_char).is_null() {
-        return 0i32;
+        return false;
     }
 
-    1
+    true
 }
 
 unsafe fn get_word(
     begin: *const libc::c_char,
     pend: *mut *const libc::c_char,
-    pto_be_quoted: *mut libc::c_int, // TODO should be bool /rtn
+    pto_be_quoted: *mut bool,
 ) {
     let mut cur: *const libc::c_char = begin;
     while *cur as libc::c_int != ' ' as i32
@@ -310,17 +309,16 @@ unsafe fn get_word(
  ******************************************************************************/
 
 /* see comment below */
-// TODO should be bool /rtn
-unsafe fn to_be_quoted(word: *const libc::c_char, size: size_t) -> libc::c_int {
+unsafe fn to_be_quoted(word: *const libc::c_char, size: size_t) -> bool {
     let mut cur: *const libc::c_char = word;
     let mut i: size_t = 0i32 as size_t;
     while i < size {
         match *cur as libc::c_int {
             44 | 58 | 33 | 34 | 35 | 36 | 64 | 91 | 92 | 93 | 94 | 96 | 123 | 124 | 125 | 126
-            | 61 | 63 | 95 => return 1i32,
+            | 61 | 63 | 95 => return true,
             _ => {
                 if *cur as libc::c_uchar as libc::c_int >= 128i32 {
-                    return 1i32;
+                    return true;
                 }
             }
         }
@@ -328,7 +326,7 @@ unsafe fn to_be_quoted(word: *const libc::c_char, size: size_t) -> libc::c_int {
         i = i.wrapping_add(1)
     }
 
-    0
+    false
 }
 
 pub unsafe fn dc_decode_header_words(in_0: *const libc::c_char) -> *mut libc::c_char {
@@ -616,8 +614,7 @@ pub unsafe fn dc_decode_modified_utf7(
     res
 }
 
-// TODO should be bool /rtn
-pub unsafe fn dc_needs_ext_header(mut to_check: *const libc::c_char) -> libc::c_int {
+pub unsafe fn dc_needs_ext_header(mut to_check: *const libc::c_char) -> bool {
     if !to_check.is_null() {
         while 0 != *to_check {
             if 0 == isalnum(*to_check as libc::c_int)
@@ -626,13 +623,13 @@ pub unsafe fn dc_needs_ext_header(mut to_check: *const libc::c_char) -> libc::c_
                 && *to_check as libc::c_int != '.' as i32
                 && *to_check as libc::c_int != '~' as i32
             {
-                return 1i32;
+                return true;
             }
             to_check = to_check.offset(1isize)
         }
     }
 
-    0
+    false
 }
 
 pub unsafe fn dc_encode_ext_header(to_encode: *const libc::c_char) -> *mut libc::c_char {
diff --git a/tests/stress.rs b/tests/stress.rs
index 82d7c8155..7a2384281 100644
--- a/tests/stress.rs
+++ b/tests/stress.rs
@@ -930,7 +930,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
     } else {
     };
     free(s as *mut libc::c_void);
-    if 0 != (0 != dc_may_be_valid_addr(0 as *const libc::c_char)) as libc::c_int as libc::c_long {
+    if 0 != (dc_may_be_valid_addr(0 as *const libc::c_char)) as libc::c_int as libc::c_long {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
                 .as_ptr(),
@@ -940,7 +940,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+    if 0 != (dc_may_be_valid_addr(b"\x00" as *const u8 as *const libc::c_char)) as libc::c_int
         as libc::c_long
     {
         __assert_rtn(
@@ -952,7 +952,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 == dc_may_be_valid_addr(b"user@domain.tld\x00" as *const u8 as *const libc::c_char))
+    if 0 != (!dc_may_be_valid_addr(b"user@domain.tld\x00" as *const u8 as *const libc::c_char))
         as libc::c_int as libc::c_long
     {
         __assert_rtn(
@@ -964,8 +964,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"uuu\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"uuu\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -976,8 +976,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"dd.tt\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"dd.tt\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -988,7 +988,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"tt.dd@uu\x00" as *const u8 as *const libc::c_char))
+    if 0 != (dc_may_be_valid_addr(b"tt.dd@uu\x00" as *const u8 as *const libc::c_char))
         as libc::c_int as libc::c_long
     {
         __assert_rtn(
@@ -1000,8 +1000,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"uu\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"uu\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -1012,8 +1012,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"u@d\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"u@d\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -1024,8 +1024,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"u@d.\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"u@d.\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -1036,8 +1036,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"u@d.t\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"u@d.t\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -1048,7 +1048,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 == dc_may_be_valid_addr(b"u@d.tt\x00" as *const u8 as *const libc::c_char))
+    if 0 != (!dc_may_be_valid_addr(b"u@d.tt\x00" as *const u8 as *const libc::c_char))
         as libc::c_int as libc::c_long
     {
         __assert_rtn(
@@ -1060,8 +1060,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"u@.tt\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"u@.tt\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -1072,8 +1072,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_may_be_valid_addr(b"@d.tt\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_may_be_valid_addr(b"@d.tt\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -2127,7 +2127,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
     } else {
     };
     free(buf1 as *mut libc::c_void);
-    if 0 != (0 == dc_needs_ext_header(b"Bj\xc3\xb6rn\x00" as *const u8 as *const libc::c_char))
+    if 0 != (!dc_needs_ext_header(b"Bj\xc3\xb6rn\x00" as *const u8 as *const libc::c_char))
         as libc::c_int as libc::c_long
     {
         __assert_rtn(
@@ -2139,8 +2139,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_needs_ext_header(b"Bjoern\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (dc_needs_ext_header(b"Bjoern\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -2151,7 +2151,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_needs_ext_header(b"\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+    if 0 != (dc_needs_ext_header(b"\x00" as *const u8 as *const libc::c_char)) as libc::c_int
         as libc::c_long
     {
         __assert_rtn(
@@ -2163,7 +2163,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 == dc_needs_ext_header(b" \x00" as *const u8 as *const libc::c_char)) as libc::c_int
+    if 0 != (!dc_needs_ext_header(b" \x00" as *const u8 as *const libc::c_char)) as libc::c_int
         as libc::c_long
     {
         __assert_rtn(
@@ -2175,8 +2175,8 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 == dc_needs_ext_header(b"a b\x00" as *const u8 as *const libc::c_char))
-        as libc::c_int as libc::c_long
+    if 0 != (!dc_needs_ext_header(b"a b\x00" as *const u8 as *const libc::c_char)) as libc::c_int
+        as libc::c_long
     {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
@@ -2187,7 +2187,7 @@ unsafe extern "C" fn stress_functions(context: &dc_context_t) {
         );
     } else {
     };
-    if 0 != (0 != dc_needs_ext_header(0 as *const libc::c_char)) as libc::c_int as libc::c_long {
+    if 0 != (dc_needs_ext_header(0 as *const libc::c_char)) as libc::c_int as libc::c_long {
         __assert_rtn(
             (*::std::mem::transmute::<&[u8; 17], &[libc::c_char; 17]>(b"stress_functions\x00"))
                 .as_ptr(),