Some testing

main.c

@@ -7,6 +7,7 @@
 #include <string.h>
 
 #define LED_PIN PD6
+#define RANDOM
 
 void exit_blink() {
     for (int i = 0; i < 4; i++) {
@@ -26,6 +27,30 @@ void enter_blink() {
     }
 }
 
+void test_mulmod() {
+    ASSERT_EQ(mulmod(3, 2, 4), 2);
+    ASSERT_EQ((3 * 2) % 4, 2);
+
+    ASSERT_EQ(mulmod(31, 3, 8), 5);
+    ASSERT_EQ(mulmod((u64)1 << 63, 2, 1000000007ULL), 582344008);
+}
+
+void test_modexp() {
+    ASSERT_EQ(modexp(3, 2, 4), 1);
+    ASSERT_EQ((3 ^ 2) % 4, 1);
+
+    ASSERT_EQ(modexp(31, 3, 8), 7);
+    ASSERT_EQ(modexp((u64)1 << 63, 2, 1000000007ULL), 319908071);
+}
+
+void debug_string(char *str) {
+    printf("Got string: %s\n", str);
+    for (int i = 0; i < strlen(str); i++) {
+        printf("decoded[%d] = '%c' (ASCII: %d)\n", i, str[i],
+               str[i]); // Print decoded chars and ASCII values
+    }
+}
+
 int main() {
     SystemInit();
     sprand(0);
@@ -36,43 +61,79 @@ int main() {
     enter_blink();
 
 #ifdef RANDOM
-    uint64_t p = gen_prime(1 << 15, 1 << 16);
-    uint64_t q = p;
+#define W 16
+    const int64_t p = gen_prime(1 << (W - 1), 1 << W);
 
-    while (p == q) p = gen_prime(1 << 15, 1 << 16);
+    int64_t qprev = p;
+    while (p == qprev) qprev = gen_prime(1 << (W - 1), 1 << W);
+
+    const i64 q = qprev;
+#undef W
 #else
-    uint64_t p = 56857;
-    uint64_t q = 47963;
+    int64_t p = 56857;
+    int64_t q = 47963;
 #endif
 
-    uint64_t n = p * q;
-    uint64_t phi_n = (p - 1) * (q - 1);
+    int64_t n = p * q;
+    int64_t phi_n = (p - 1) * (q - 1);
 
     // 'e' is public. E for encrypt.
-    uint64_t e = 0;
-    while (gcd(e, phi_n) != 1) e = prand_range(3, phi_n - 1);
+    int64_t e = 0;
+    do {
+        e = prand_range(3, phi_n - 1);
+    } while (gcd(e, phi_n) != 1);
 
     // 'd' is our private key. D as in decrypt
-    uint64_t d = mod_inverse(e, phi_n);
+    int64_t d = mod_inverse(e, phi_n);
     if (d == 0 || d == 1) {
         printf("Modular inverse not found...");
         while (1);
     }
 
+    {
+        char test = 'o';
+        u64 enc = modexp(test, e, n);
+        char dec = (char)modexp(enc, d, n);
+
+        if (dec != test) {
+            printf("ERROR: %c != %c =>  %d != %d\n", test, dec, test, dec);
+            // while (1);
+        }
+    }
+    {
+        char test = 'c';
+
+        u64 p = 3, q = 11;
+        u64 n = p * q;
+        u64 e = 7;
+        u64 d = 3;
+        u64 enc = modexp(test, e, n);
+        char dec = (char)modexp(enc, d, n);
+
+        if (dec != test) {
+            printf("ERROR: %c != %c =>  %d != %d\n", test, dec, test, dec);
+        } else
+            printf("INFO: %c == %c => %d == %d\n", test, dec, test, dec);
+    }
+
     char msg[] = "Hello";
-    uint64_t coded[sizeof(msg)] = {0};
+    int64_t coded[sizeof(msg)] = {0};
     char decoded[sizeof(msg)] = {0};
 
     // Encode the message
-    for (int i = 0; i < sizeof(msg); i++) {
-        coded[i] = (uint64_t)modexp((uint64_t)msg[i], e, n);
+    for (int i = 0; i < strlen(msg); i++) {
+        coded[i] = modexp((int64_t)msg[i], e, n);
     }
 
     // Decode the message
-    for (int i = 0; i < sizeof(msg); i++) {
-        decoded[i] = (char)modexp(coded[i], d, n);
+    for (int i = 0; i < strlen(msg); i++) {
+        int64_t dec = modexp(coded[i], d, n);
+        decoded[i] = dec & 0xFF;
     }
 
+    test_mulmod();
+    test_modexp();
+
     {
         printf("P: %u\n", (uint32_t)p);
         printf("Q: %u\n", (uint32_t)q);
@@ -83,6 +144,12 @@ int main() {
 
         printf("Message: %s\n", msg);
         printf("Decoded: %s\n", decoded);
+
+        for (int i = 0; i < strlen(msg); i++) {
+            printf("coded[%d] = 0x%016lx\n", i, (unsigned long)coded[i]);
+        }
+
+        debug_string(decoded);
     }
 
     // Exit and hang forever