enforce integer division via explicit builtins

std/arraylist/arraylist.bro

@@ -30,7 +30,7 @@ reserve func($T type, list @mut ArrayList(T), minimum_capacity usize) void ! mem
 
 	new_capacity usize = 8
 	if list.capacity >= 8 {
-		half usize :: list.capacity / 2
+		half usize :: div_trunc(list.capacity, 2)
 		if list.capacity > max_value(usize) - half {
 			new_capacity = minimum_capacity
 		} else {

std/mem/mem.bro

@@ -61,7 +61,7 @@ alloc func($T type, allocator Allocator, count usize) []mut T ! AllocError {
 	if element_size == 0 {
 		return _empty_slice(T, count)
 	}
-	if count > max_value(usize) / element_size {
+	if count > div_trunc(max_value(usize), element_size) {
 		return .out_of_memory
 	}
 
@@ -86,7 +86,7 @@ realloc func($T type, allocator Allocator, memory []mut T, new_count usize) []mu
 	if element_size == 0 {
 		return _empty_slice(T, new_count)
 	}
-	if new_count > max_value(usize) / element_size {
+	if new_count > div_trunc(max_value(usize), element_size) {
 		return .out_of_memory
 	}
 
@@ -125,7 +125,7 @@ _power_of_two func(value usize) bool {
 
 	current usize = value
 	while current > 1 {
-		half usize = current / 2
+		half usize = div_trunc(current, 2)
 		if half * 2 != current {
 			return false
 		}