use -Wextra

Makefile

@@ -1,5 +1,5 @@
 CC     = gcc
-CFLAGS = -Wall -Os
+CFLAGS = -Wall -Wextra -Os
 OBJS   = bignum.o ecdsa.o secp256k1.o sha2.o rand.o hmac.o bip32.o ripemd160.o bip39.o pbkdf2.o
 OBJS  += aescrypt.o aeskey.o aestab.o
 

ecdsa.c

@@ -390,7 +390,7 @@ int ecdsa_address_decode(const char *addr, uint8_t *out)
 	uint8_t buf[32], check[32];
 	bn_zero(&num);
 	uint32_t k;
-	int i;
+	size_t i;
 	for (i = 0; i < strlen(addr); i++) {
 		bn_muli(&num, 58);
 		for (k = 0; k <= strlen(code); k++) {

tests.c

@@ -235,7 +235,8 @@ END_TEST
 START_TEST(test_sign_speed)
 {
 	uint8_t sig[64], priv_key[32], msg[256];
-	int i, res;
+	size_t i;
+	int res;
 
 	for (i = 0; i < sizeof(msg); i++) {
 		msg[i] = i * 1103515245;
@@ -262,7 +263,8 @@ END_TEST
 START_TEST(test_verify_speed)
 {
 	uint8_t sig[64], pub_key33[33], pub_key65[65], msg[256];
-	int i, res;
+	size_t i;
+	int res;
 
 	for (i = 0; i < sizeof(msg); i++) {
 		msg[i] = i * 1103515245;