diff --git a/toxcore/Messenger.c b/toxcore/Messenger.c
index 945d655676..93ed6495ca 100644
--- a/toxcore/Messenger.c
+++ b/toxcore/Messenger.c
@@ -28,16 +28,14 @@ static int write_cryptpacket_id(const Messenger *m, int32_t friendnumber, uint8_
                                 uint32_t length, uint8_t congestion_control);
 static void m_register_default_plugins(Messenger *m);
 
-// friend_not_valid determines if the friendnumber passed is valid in the Messenger object
-static uint8_t friend_not_valid(const Messenger *m, int32_t friendnumber)
+/**
+ * Determines if the friendnumber passed is valid in the Messenger object.
+ *
+ * @param friendnumber The index in the friend list.
+ */
+static bool friend_is_valid(const Messenger *m, int32_t friendnumber)
 {
-    if ((unsigned int)friendnumber < m->numfriends) {
-        if (m->friendlist[friendnumber].status != 0) {
-            return 0;
-        }
-    }
-
-    return 1;
+    return (unsigned int)friendnumber < m->numfriends && m->friendlist[friendnumber].status != 0;
 }
 
 /* Set the size of the friend list to numfriends.
@@ -88,7 +86,7 @@ int32_t getfriend_id(const Messenger *m, const uint8_t *real_pk)
  */
 int get_real_pk(const Messenger *m, int32_t friendnumber, uint8_t *real_pk)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -101,7 +99,7 @@ int get_real_pk(const Messenger *m, int32_t friendnumber, uint8_t *real_pk)
  */
 int getfriendcon_id(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -140,7 +138,7 @@ void getaddress(const Messenger *m, uint8_t *address)
 
 static int send_online_packet(Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return 0;
     }
 
@@ -301,7 +299,7 @@ int32_t m_addfriend_norequest(Messenger *m, const uint8_t *real_pk)
 
 static int clear_receipts(Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -320,7 +318,7 @@ static int clear_receipts(Messenger *m, int32_t friendnumber)
 
 static int add_receipt(Messenger *m, int32_t friendnumber, uint32_t packet_num, uint32_t msg_id)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -349,7 +347,7 @@ static int add_receipt(Messenger *m, int32_t friendnumber, uint32_t packet_num,
  */
 static int friend_received_packet(const Messenger *m, int32_t friendnumber, uint32_t number)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -359,7 +357,7 @@ static int friend_received_packet(const Messenger *m, int32_t friendnumber, uint
 
 static int do_receipts(Messenger *m, int32_t friendnumber, void *userdata)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -397,7 +395,7 @@ static int do_receipts(Messenger *m, int32_t friendnumber, void *userdata)
  */
 int m_delfriend(Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -435,7 +433,7 @@ int m_delfriend(Messenger *m, int32_t friendnumber)
 
 int m_get_friend_connectionstatus(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -463,7 +461,7 @@ int m_get_friend_connectionstatus(const Messenger *m, int32_t friendnumber)
 
 int m_friend_exists(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return 0;
     }
 
@@ -487,7 +485,7 @@ int m_send_message_generic(Messenger *m, int32_t friendnumber, uint8_t type, con
         return -5;
     }
 
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         LOGGER_ERROR(m->log, "Friend number %d is invalid", friendnumber);
         return -1;
     }
@@ -548,7 +546,7 @@ static int m_sendname(const Messenger *m, int32_t friendnumber, const uint8_t *n
  */
 int setfriendname(Messenger *m, int32_t friendnumber, const uint8_t *name, uint16_t length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -617,7 +615,7 @@ uint16_t getself_name(const Messenger *m, uint8_t *name)
  */
 int getname(const Messenger *m, int32_t friendnumber, uint8_t *name)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -627,7 +625,7 @@ int getname(const Messenger *m, int32_t friendnumber, uint8_t *name)
 
 int m_get_name_size(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -689,7 +687,7 @@ int m_set_userstatus(Messenger *m, uint8_t status)
  */
 int m_get_statusmessage_size(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -701,7 +699,7 @@ int m_get_statusmessage_size(const Messenger *m, int32_t friendnumber)
  */
 int m_copy_statusmessage(const Messenger *m, int32_t friendnumber, uint8_t *buf, uint32_t maxlen)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -730,7 +728,7 @@ int m_copy_self_statusmessage(const Messenger *m, uint8_t *buf)
 
 uint8_t m_get_userstatus(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return USERSTATUS_INVALID;
     }
 
@@ -750,7 +748,7 @@ uint8_t m_get_self_userstatus(const Messenger *m)
 
 uint64_t m_get_last_online(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return UINT64_MAX;
     }
 
@@ -763,7 +761,7 @@ int m_set_usertyping(Messenger *m, int32_t friendnumber, uint8_t is_typing)
         return -1;
     }
 
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -779,7 +777,7 @@ int m_set_usertyping(Messenger *m, int32_t friendnumber, uint8_t is_typing)
 
 int m_get_istyping(const Messenger *m, int32_t friendnumber)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -804,7 +802,7 @@ static int send_user_istyping(const Messenger *m, int32_t friendnumber, uint8_t
 
 static int set_friend_statusmessage(const Messenger *m, int32_t friendnumber, const uint8_t *status, uint16_t length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -952,7 +950,7 @@ static void set_friend_status(Messenger *m, int32_t friendnumber, uint8_t status
 static int write_cryptpacket_id(const Messenger *m, int32_t friendnumber, uint8_t packet_id, const uint8_t *data,
                                 uint32_t length, uint8_t congestion_control)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return 0;
     }
 
@@ -1033,7 +1031,7 @@ void callback_file_reqchunk(Messenger *m, m_file_chunk_request_cb *function)
  */
 int file_get_id(const Messenger *m, int32_t friendnumber, uint32_t filenumber, uint8_t *file_id)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1082,7 +1080,7 @@ int file_get_id(const Messenger *m, int32_t friendnumber, uint32_t filenumber, u
 static int file_sendrequest(const Messenger *m, int32_t friendnumber, uint8_t filenumber, uint32_t file_type,
                             uint64_t filesize, const uint8_t *file_id, const uint8_t *filename, uint16_t filename_length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return 0;
     }
 
@@ -1116,7 +1114,7 @@ static int file_sendrequest(const Messenger *m, int32_t friendnumber, uint8_t fi
 long int new_filesender(const Messenger *m, int32_t friendnumber, uint32_t file_type, uint64_t filesize,
                         const uint8_t *file_id, const uint8_t *filename, uint16_t filename_length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1195,7 +1193,7 @@ static int send_file_control_packet(const Messenger *m, int32_t friendnumber, ui
  */
 int file_control(const Messenger *m, int32_t friendnumber, uint32_t filenumber, unsigned int control)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1296,7 +1294,7 @@ int file_control(const Messenger *m, int32_t friendnumber, uint32_t filenumber,
  */
 int file_seek(const Messenger *m, int32_t friendnumber, uint32_t filenumber, uint64_t position)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1352,7 +1350,7 @@ int file_seek(const Messenger *m, int32_t friendnumber, uint32_t filenumber, uin
 static int64_t send_file_data_packet(const Messenger *m, int32_t friendnumber, uint8_t filenumber, const uint8_t *data,
                                      uint16_t length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1384,7 +1382,7 @@ static int64_t send_file_data_packet(const Messenger *m, int32_t friendnumber, u
 int file_data(const Messenger *m, int32_t friendnumber, uint32_t filenumber, uint64_t position, const uint8_t *data,
               uint16_t length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1455,7 +1453,7 @@ int file_data(const Messenger *m, int32_t friendnumber, uint32_t filenumber, uin
  */
 uint64_t file_dataremaining(const Messenger *m, int32_t friendnumber, uint8_t filenumber, uint8_t send_receive)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return 0;
     }
 
@@ -1776,7 +1774,7 @@ static int m_handle_lossy_packet(void *object, int friend_num, const uint8_t *pa
 {
     Messenger *m = (Messenger *)object;
 
-    if (friend_not_valid(m, friend_num)) {
+    if (!friend_is_valid(m, friend_num)) {
         return 1;
     }
 
@@ -1806,7 +1804,7 @@ void custom_lossy_packet_registerhandler(Messenger *m, m_friend_lossy_packet_cb
 int m_callback_rtp_packet(Messenger *m, int32_t friendnumber, uint8_t byte, m_lossy_rtp_packet_cb *function,
                           void *object)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1829,7 +1827,7 @@ int m_callback_rtp_packet(Messenger *m, int32_t friendnumber, uint8_t byte, m_lo
  */
 int m_send_custom_lossy_packet(const Messenger *m, int32_t friendnumber, const uint8_t *data, uint32_t length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
@@ -1859,7 +1857,7 @@ static int handle_custom_lossless_packet(void *object, int friend_num, const uin
 {
     Messenger *m = (Messenger *)object;
 
-    if (friend_not_valid(m, friend_num)) {
+    if (!friend_is_valid(m, friend_num)) {
         return -1;
     }
 
@@ -1881,7 +1879,7 @@ void custom_lossless_packet_registerhandler(Messenger *m, m_friend_lossless_pack
 
 int send_custom_lossless_packet(const Messenger *m, int32_t friendnumber, const uint8_t *data, uint32_t length)
 {
-    if (friend_not_valid(m, friendnumber)) {
+    if (!friend_is_valid(m, friendnumber)) {
         return -1;
     }
 
diff --git a/toxcore/TCP_connection.c b/toxcore/TCP_connection.c
index 3dd8652ead..adef31751f 100644
--- a/toxcore/TCP_connection.c
+++ b/toxcore/TCP_connection.c
@@ -100,44 +100,44 @@ static int realloc_TCP_con(TCP_con **array, size_t num)
 }
 
 
-/* return 1 if the connections_number is not valid.
- * return 0 if the connections_number is valid.
+/**
+ * Return true if the connections_number is valid.
  */
-static bool connections_number_not_valid(const TCP_Connections *tcp_c, int connections_number)
+static bool connections_number_is_valid(const TCP_Connections *tcp_c, int connections_number)
 {
     if ((unsigned int)connections_number >= tcp_c->connections_length) {
-        return 1;
+        return false;
     }
 
     if (tcp_c->connections == nullptr) {
-        return 1;
+        return false;
     }
 
     if (tcp_c->connections[connections_number].status == TCP_CONN_NONE) {
-        return 1;
+        return false;
     }
 
-    return 0;
+    return true;
 }
 
-/* return 1 if the tcp_connections_number is not valid.
- * return 0 if the tcp_connections_number is valid.
+/**
+ * Return true if the tcp_connections_number is valid.
  */
-static bool tcp_connections_number_not_valid(const TCP_Connections *tcp_c, int tcp_connections_number)
+static bool tcp_connections_number_is_valid(const TCP_Connections *tcp_c, int tcp_connections_number)
 {
     if ((unsigned int)tcp_connections_number >= tcp_c->tcp_connections_length) {
-        return 1;
+        return false;
     }
 
     if (tcp_c->tcp_connections == nullptr) {
-        return 1;
+        return false;
     }
 
     if (tcp_c->tcp_connections[tcp_connections_number].status == TCP_CONN_NONE) {
-        return 1;
+        return false;
     }
 
-    return 0;
+    return true;
 }
 
 /* Create a new empty connection.
@@ -199,7 +199,7 @@ static int create_tcp_connection(TCP_Connections *tcp_c)
  */
 static int wipe_connection(TCP_Connections *tcp_c, int connections_number)
 {
-    if (connections_number_not_valid(tcp_c, connections_number)) {
+    if (!connections_number_is_valid(tcp_c, connections_number)) {
         return -1;
     }
 
@@ -227,7 +227,7 @@ static int wipe_connection(TCP_Connections *tcp_c, int connections_number)
  */
 static int wipe_tcp_connection(TCP_Connections *tcp_c, int tcp_connections_number)
 {
-    if (tcp_connections_number_not_valid(tcp_c, tcp_connections_number)) {
+    if (!tcp_connections_number_is_valid(tcp_c, tcp_connections_number)) {
         return -1;
     }
 
@@ -250,7 +250,7 @@ static int wipe_tcp_connection(TCP_Connections *tcp_c, int tcp_connections_numbe
 
 static TCP_Connection_to *get_connection(const TCP_Connections *tcp_c, int connections_number)
 {
-    if (connections_number_not_valid(tcp_c, connections_number)) {
+    if (!connections_number_is_valid(tcp_c, connections_number)) {
         return nullptr;
     }
 
@@ -259,7 +259,7 @@ static TCP_Connection_to *get_connection(const TCP_Connections *tcp_c, int conne
 
 static TCP_con *get_tcp_connection(const TCP_Connections *tcp_c, int tcp_connections_number)
 {
-    if (tcp_connections_number_not_valid(tcp_c, tcp_connections_number)) {
+    if (!tcp_connections_number_is_valid(tcp_c, tcp_connections_number)) {
         return nullptr;
     }
 
diff --git a/toxcore/net_crypto.c b/toxcore/net_crypto.c
index fb69b7685f..2851053bbf 100644
--- a/toxcore/net_crypto.c
+++ b/toxcore/net_crypto.c
@@ -174,23 +174,23 @@ DHT *nc_get_dht(const Net_Crypto *c)
     return c->dht;
 }
 
-static uint8_t crypt_connection_id_not_valid(const Net_Crypto *c, int crypt_connection_id)
+static bool crypt_connection_id_is_valid(const Net_Crypto *c, int crypt_connection_id)
 {
     if ((uint32_t)crypt_connection_id >= c->crypto_connections_length) {
-        return 1;
+        return false;
     }
 
     if (c->crypto_connections == nullptr) {
-        return 1;
+        return false;
     }
 
     const Crypto_Conn_State status = c->crypto_connections[crypt_connection_id].status;
 
     if (status == CRYPTO_CONN_NO_CONNECTION || status == CRYPTO_CONN_FREE) {
-        return 1;
+        return false;
     }
 
-    return 0;
+    return true;
 }
 
 /* cookie timeout in seconds */
@@ -555,7 +555,7 @@ static int handle_crypto_handshake(const Net_Crypto *c, uint8_t *nonce, uint8_t
 
 static Crypto_Connection *get_crypto_connection(const Net_Crypto *c, int crypt_connection_id)
 {
-    if (crypt_connection_id_not_valid(c, crypt_connection_id)) {
+    if (!crypt_connection_id_is_valid(c, crypt_connection_id)) {
         return nullptr;
     }
 
@@ -1858,7 +1858,7 @@ static int wipe_crypto_connection(Net_Crypto *c, int crypt_connection_id)
 static int getcryptconnection_id(const Net_Crypto *c, const uint8_t *public_key)
 {
     for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
-        if (crypt_connection_id_not_valid(c, i)) {
+        if (!crypt_connection_id_is_valid(c, i)) {
             continue;
         }