kernel: replace random number generator with mersenne twister

include/kernel/util.h

@@ -61,6 +61,7 @@ extern uint64_t host_to_little_u64(uint64_t v);
 extern uint64_t big_to_host_u64(uint64_t v);
 extern uint64_t little_to_host_u64(uint64_t v);
 
+extern void init_random(uint64_t seed);
 extern bool fill_random(void *buffer, unsigned int size);
 
 #ifdef __cplusplus

util/random.c

@@ -1,35 +1,81 @@
 #include <kernel/util.h>
 
-static unsigned int random_seed = 53455346;
+typedef uint64_t word_t;
+#define STATE_SIZE 312
+#define MIDDLE     156
+#define INIT_SHIFT 62
+#define TWIST_MASK 0xb5026f5aa96619e9
+#define INIT_FACT  6364136223846793005
+#define SHIFT1     29
+#define MASK1      0x5555555555555555
+#define SHIFT2     17
+#define MASK2      0x71d67fffeda60000
+#define SHIFT3     37
+#define MASK3      0xfff7eee000000000
+#define SHIFT4     43
+
+#define LOWER_MASK 0x7fffffff
+#define UPPER_MASK (~(word_t)LOWER_MASK)
+static word_t state[STATE_SIZE];
+static size_t index = STATE_SIZE + 1;
+
+static void seed(word_t s)
+{
+	index = STATE_SIZE;
+	state[0] = s;
+	for (size_t i = 1; i < STATE_SIZE; i++) {
+		state[i] = (INIT_FACT
+		            * (state[i - 1] ^ (state[i - 1] >> INIT_SHIFT)))
+		         + i;
+	}
+}
+
+static void twist(void)
+{
+	for (size_t i = 0; i < STATE_SIZE; i++) {
+		word_t x = (state[i] & UPPER_MASK)
+		         | (state[(i + 1) % STATE_SIZE] & LOWER_MASK);
+		x = (x >> 1) ^ (x & 1 ? TWIST_MASK : 0);
+		state[i] = state[(i + MIDDLE) % STATE_SIZE] ^ x;
+	}
+
+	index = 0;
+}
+
+static word_t mt_random(void)
+{
+	if (index >= STATE_SIZE) {
+		twist();
+	}
+
+	word_t y = state[index];
+	y ^= (y >> SHIFT1) & MASK1;
+	y ^= (y << SHIFT2) & MASK2;
+	y ^= (y << SHIFT3) & MASK3;
+	y ^= y >> SHIFT4;
+
+	index++;
+	return y;
+}
+
+void init_random(uint64_t seedvalue)
+{
+	seed(seedvalue);
+}
 
 bool fill_random(void *p, unsigned int size)
 {
-	unsigned char *buffer = p;
+	unsigned char *dst = p;
+	uint64_t w = mt_random();
+	unsigned char *src = (unsigned char *)&w;
 
-	if (!buffer || !size) {
-		return false;
+	for (size_t i = 0, j = 0; i < size; i++, j++) {
+		dst[i] = src[j];
+
+		if (j == (sizeof w) - 1) {
+			w = mt_random();
+			j = 0;
 		}
-
-	for (uint32_t i = 0; i < size; i++) {
-		uint32_t next = random_seed;
-		uint32_t result;
-
-		next *= 1103515245;
-		next += 12345;
-		result = (uint32_t)(next / 65536) % 2048;
-
-		next *= 1103515245;
-		next += 12345;
-		result <<= 10;
-		result ^= (uint32_t)(next / 65536) % 1024;
-
-		next *= 1103515245;
-		next += 12345;
-		result <<= 10;
-		result ^= (uint32_t)(next / 65536) % 1024;
-		random_seed = next;
-
-		buffer[i] = (uint8_t)(result % 256);
 	}
 
 	return true;