Call sodium_init(), skip AES-256-GCM benchmark if not supported

--- Regarding sodium_init() ---

From https://libsodium.gitbook.io/doc/usage:

sodium_init() initializes the library and should be called before any other function provided by Sodium.

Interestingly, only the ChaCha20-Poly1305 benchmark was severely affected by the missing initialization: ~20 seconds instead of ~6.5 on my machine.

--- Regarding AES-256-GCM ---

From https://libsodium.gitbook.io/doc/secret-key_cryptography/aead/aes-256-gcm:

The current implementation of this construction is hardware-accelerated and requires the Intel SSSE3 extensions, as well as the aesni and pclmul instructions.

Intel Westmere processors (introduced in 2010) and newer meet the requirements.

There are no plans to support non hardware-accelerated implementations of AES-GCM. If portability is a concern, use ChaCha20-Poly1305 instead.

Before using the functions below, hardware support for AES can be checked with:

int crypto_aead_aes256gcm_is_available(void);

The function returns 1 if the current CPU supports the AES256-GCM implementation, and 0 if it doesn't.

The library must have been initialized with sodium_init() prior to calling this function.

sodium.c

@@ -4,17 +4,26 @@
 #include <sodium.h>
 
 bool sodium_main(const size_t message_size, const size_t iterations) {
+	if (sodium_init() == -1) {
+		printf("sodium_main(): sodium_init() failed!\n");
+		return false;
+	}
+
 	unsigned char message[message_size], out[message_size];
 	randombytes_buf(message, sizeof(message));
 
 	double elapsed;
 
-	if (!(elapsed = sodium_aes_256_gcm(iterations, out, sizeof(message), message))) {
-		printf("sodium_main(): sodium_aes_256_gcm() failed!\n");
-		return false;
-	}
+	if (crypto_aead_aes256gcm_is_available()) {
+		if (!(elapsed = sodium_aes_256_gcm(iterations, out, sizeof(message), message))) {
+			printf("sodium_main(): sodium_aes_256_gcm() failed!\n");
+			return false;
+		}
 
-	printf("[libsodium] AES-256-GCM took %f seconds for %zu iterations, %zu bytes message\n", elapsed, iterations, message_size);
+		printf("[libsodium] AES-256-GCM took %f seconds for %zu iterations, %zu bytes message\n", elapsed, iterations, message_size);
+	} else {
+		printf("[libsodium] skipping AES-256-GCM benchmark due to missing requirements. SSSE3 extensions, \"aesni\" and \"pclmul\" instructions are required.\n");
+	}
 
 	if (!(elapsed = sodium_chacha20_poly1305(iterations, out, sizeof(message), message))) {
 		printf("sodium_main(): sodium_chacha20_poly1305() failed!\n");