rand: change rand.seed() to receive seed value

vlib/bf/bf_test.v

@@ -1,6 +1,7 @@
 import bf
 
 import rand
+import time
 
 fn test_bf_new_size() {
 	instance := bf.new(75)
@@ -18,7 +19,7 @@ fn test_bf_set_clear_toggle_get() {
 }
 
 fn test_bf_and_not_or_xor() {
-	rand.seed()
+	rand.seed(time.now().uni)
 	len := 80
 	mut input1 := bf.new(len)
 	mut input2 := bf.new(len)
@@ -45,7 +46,7 @@ fn test_bf_and_not_or_xor() {
 }
 
 fn test_clone_cmp() {
-	rand.seed()
+	rand.seed(time.now().uni)
 	len := 80
 	mut input := bf.new(len)
 	for i := 0; i < len; i++ {
@@ -59,7 +60,7 @@ fn test_clone_cmp() {
 }
 
 fn test_slice_join() {
-	rand.seed()
+	rand.seed(time.now().uni)
 	len := 80
 	mut input := bf.new(len)
 	for i := 0; i < len; i++ {
@@ -82,7 +83,7 @@ fn test_slice_join() {
 }
 
 fn test_popcount() {
-	rand.seed()
+	rand.seed(time.now().uni)
 	len := 80
 	mut count0 := 0
 	mut input := bf.new(len)
@@ -97,7 +98,7 @@ fn test_popcount() {
 }
 
 fn test_hamming() {
-	rand.seed()
+	rand.seed(time.now().uni)
 	len := 80
 	mut count := 0
 	mut input1 := bf.new(len)

vlib/rand/rand.v

@@ -4,10 +4,8 @@
 
 module rand
 
-import time
-
-pub fn seed() {
-	C.srand(time.now().uni)
+pub fn seed(s int) {
+	C.srand(s)
 }
 
 pub fn next(max int) int {
@@ -15,4 +13,3 @@ pub fn next(max int) int {
 }
 
 fn C.rand() int 
-

vlib/rand/rand_test.v

@@ -0,0 +1,30 @@
+import rand
+
+fn gen_randoms(seed int) []int {
+	mut randoms := [0; 20]
+	rand.seed(seed)
+	for i in 0..20 {
+		randoms[i] = rand.next(100)
+	}
+	return randoms
+}
+
+fn test_rand_reproducibility() {
+	mut randoms1 := gen_randoms(42)
+	mut randoms2 := gen_randoms(42)
+	assert randoms1.len == randoms2.len
+
+	mut len := randoms1.len
+	for i in 0..len {
+		assert randoms1[i] == randoms2[i]
+	}
+
+	randoms1 = gen_randoms(256)
+	randoms2 = gen_randoms(256)
+	assert randoms1.len == randoms2.len
+
+	len = randoms1.len
+	for i in 0..len {
+		assert randoms1[i] == randoms2[i]
+	}
+}