Update randint to have a more uniform distribution on range [0, limit]

Signed-off-by: Siddharth Chandrasekaran <[email protected]>

include/utils/utils.h

@@ -117,11 +117,11 @@
 #define __weak          __attribute__((weak))
 
 /**
- * @brief Return random number between `min` and `max` both inclusive.
+ * @brief Return random number between 0 and `limit` both inclusive.
  *
  * Note: the random number generator must be pre-seeded.
  */
-int randint(int min, int max);
+int randint(int limit);
 
 /**
  * @brief Rounds up 32-bit v to nearest power of 2. If v is already a power

src/utils.c

@@ -13,9 +13,15 @@
 
 #include <utils/utils.h>
 
-int randint(int min, int max)
+int randint(int limit)
 {
-	return (rand() % (max - min + 1)) + min;
+	int r;
+	int divisor = RAND_MAX / (limit + 1);
+
+	do {
+		r = rand() / divisor;
+	} while (r > limit);
+	return r;
 }
 
 uint32_t round_up_pow2(uint32_t v)

tests/test-bus-server.c

@@ -20,7 +20,7 @@ int bus_write_check(int *fd)
 	char buf[128];
 	int i, write_fd;
 
-	write_fd = randint(0, NUM_CLIENTS - 1);
+	write_fd = randint(NUM_CLIENTS - 1);
 	ret = write(fd[write_fd], TEST_MSG, TEST_MSG_LEN);
 	if (ret != TEST_MSG_LEN) {
 		mod_printf("write %d failed!", write_fd);