tests: map: Enhance random number generator

mk/tests.mk

@@ -10,7 +10,8 @@ CACHE_TEST_OBJS := \
 	test-cache.o
 
 MAP_TEST_OBJS := \
-	test-map.o
+	test-map.o \
+	mt19937.o
 
 CACHE_TEST_OBJS := $(addprefix $(CACHE_TEST_OUTDIR)/, $(CACHE_TEST_OBJS)) \
 		   $(OUT)/cache.o $(OUT)/mpool.o

tests/map/mt19937.c

@@ -0,0 +1,46 @@
+/*
+ * rv32emu is freely redistributable under the MIT License. See the file
+ * "LICENSE" for information on usage and redistribution of this file.
+ */
+
+#include "mt19937.h"
+
+static uint64_t MT[624];
+static uint64_t index = 0;
+
+void mt19937_init(uint64_t seed)
+{
+    MT[0] = seed;
+    for (int i = 1; i < 624; i++) {
+        MT[i] = 0xffffffffULL &
+                (0x6c078965ULL * (MT[i - 1] ^ (MT[i - 1] >> 30)) + i);
+    }
+}
+
+static void generate_numbers()
+{
+    for (int i = 0; i < 624; i++) {
+        uint64_t y =
+            (MT[i] & 0x80000000ULL) + (MT[(i + 1) % 624] & 0x7fffffffULL);
+        MT[i] = MT[(i + 397) % 624] ^ (y >> 1);
+        if (y % 2 != 0) {
+            MT[i] = MT[i] ^ 0x9908b0dfULL;
+        }
+    }
+}
+
+uint64_t mt19937_extract()
+{
+    if (index == 0) {
+        generate_numbers();
+    }
+
+    uint64_t y = MT[index];
+    y = y ^ (y >> 11);
+    y = y ^ ((y << 7) & 0x9d2c5680ULL);
+    y = y ^ ((y << 15) & 0xefc60000ULL);
+    y = y ^ (y >> 18);
+
+    index = (index + 1) % 624;
+    return y;
+}

tests/map/mt19937.h

@@ -0,0 +1,20 @@
+/*
+ * rv32emu is freely redistributable under the MIT License. See the file
+ * "LICENSE" for information on usage and redistribution of this file.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+/*
+ * This is a pseudorandom number generator implemented using the mt19937 32-bit
+ * algorithm. For more information on the mt19937 algorithm, please refer to the
+ * Wikipedia page: https://en.wikipedia.org/wiki/Mersenne_Twister
+ */
+
+/* Initialize the random number generator with a seed */
+void mt19937_init(uint64_t seed);
+
+/* Generate and extract a 32-bit random number */
+uint64_t mt19937_extract();

tests/map/test-map.c

@@ -5,6 +5,7 @@
 #include <time.h>
 
 #include "map.h"
+#include "mt19937.h"
 
 static void swap(int *x, int *y)
 {
@@ -31,12 +32,9 @@ static int test_map_mixed_operations()
         val[i] = i + 1;
     }
 
-    /* TODO: This is not a reconmended way to randomize stuff, just a simple
-     * test. Using MT19937 might be better
-     */
     for (int i = 0; i < N_NODES; i++) {
-        int pos_a = rand() % N_NODES;
-        int pos_b = rand() % N_NODES;
+        int pos_a = mt19937_extract() % N_NODES;
+        int pos_b = mt19937_extract() % N_NODES;
         swap(&key[pos_a], &key[pos_b]);
         swap(&val[pos_a], &val[pos_b]);
     }
@@ -107,7 +105,7 @@ int main(int argc, char *argv[])
     (void) argc;
     (void) argv;
 
-    srand((unsigned) time(NULL));
+    mt19937_init(time(NULL));
 
     return test_map_mixed_operations();
 }