base32: Add base32_decoded_length

base32.c

@@ -63,6 +63,12 @@ size_t base32_encoded_length(size_t inlen) {
 	return (inlen / 5) * 8 + (remainder * 8 + 4) / 5;
 }
 
+size_t base32_decoded_length(size_t inlen) {
+	uint8_t remainder = inlen % 8;
+
+	return (inlen / 8) * 5 + (remainder * 5) / 8;
+}
+
 void base32_5to8(const uint8_t *in, uint8_t length, uint8_t *out) {
 	if (length >= 1) {
 		out[0]  = (in[0] >> 3);

base32.h

@@ -33,5 +33,6 @@ bool base32_encode(const uint8_t *in, size_t inlen, char *out, size_t outlen, co
 void base32_encode_unsafe(const uint8_t *in, size_t inlen, uint8_t *out);
 
 size_t base32_encoded_length(size_t inlen);
+size_t base32_decoded_length(size_t inlen);
 
 #endif

test_check.c

@@ -518,15 +518,17 @@ START_TEST(test_base32_rfc4648)
 	char buffer[64];
 
 	for (size_t i = 0; i < (sizeof(tests) / sizeof(*tests)); i++) {
-		const char *input  = tests[i].input;
-		const char *output = tests[i].output;
+		const char *in  = tests[i].input;
+		const char *out = tests[i].output;
 
-		size_t inlen = strlen(input);
-		size_t outlen = base32_encoded_length(inlen);
-		ck_assert_int_eq(outlen, strlen(output));
+		size_t inlen = strlen(in);
+		size_t outlen = strlen(out);
 
-		base32_encode((uint8_t *) input, inlen, buffer, sizeof(buffer), BASE32_ALPHABET_RFC4648);
-		ck_assert_str_eq(buffer, output);
+		ck_assert_int_eq(outlen, base32_encoded_length(inlen));
+		ck_assert_int_eq(inlen, base32_decoded_length(outlen));
+
+		base32_encode((uint8_t *) in, inlen, buffer, sizeof(buffer), BASE32_ALPHABET_RFC4648);
+		ck_assert_str_eq(buffer, out);
 	}
 }
 END_TEST