array: add `reverse_in_place` for performance (#5798)

vlib/builtin/array.v

@@ -400,6 +400,21 @@ pub fn (mut a3 array) push_many(val voidptr, size int) {
 	a3.len += size
 }
 
+pub fn (mut a array) reverse_in_place() {
+	if a.len < 2 {
+		return
+	}
+	unsafe {
+		mut tmp_value := malloc(a.element_size)
+		for i in 0..a.len/2 {
+			C.memcpy(tmp_value, byteptr(a.data) + i * a.element_size, a.element_size)
+			C.memcpy(byteptr(a.data) + i * a.element_size, byteptr(a.data) + (a.len-1-i) * a.element_size, a.element_size)
+			C.memcpy(byteptr(a.data) + (a.len-1-i) * a.element_size, tmp_value, a.element_size)
+		}
+		free(tmp_value)
+	}
+}
+
 // array.reverse returns a new array with the elements of
 // the original array in reverse order.
 pub fn (a array) reverse() array {

vlib/builtin/array_test.v

@@ -932,3 +932,17 @@ fn test_array_add_in_mut() {
 	add_nums(mut nums)
 	assert nums == [1, 2, 3, 4]
 }
+
+fn test_reverse_in_place() {
+	mut a := [1, 2, 3, 4]
+	a.reverse_in_place()
+	assert a == [4, 3, 2, 1]
+
+	mut b := ['a', 'b', 'c']
+	b.reverse_in_place()
+	assert b == ['c', 'b', 'a']
+
+	mut c := [[1, 2], [3, 4], [5, 6]]
+	c.reverse_in_place()
+	assert c == [[5, 6], [3, 4], [1, 2]]
+}