1 files changed, 14 insertions, 1 deletions
diff --git a/aoc-2020-gleam/src/ext/intx.gleam b/aoc-2020-gleam/src/ext/intx.gleam
index 077b4f2..5c9bcc0 100644
--- a/aoc-2020-gleam/src/ext/intx.gleam
+++ b/aoc-2020-gleam/src/ext/intx.gleam
@@ -1,4 +1,5 @@
 import gleam/int
+import gleam/bool
 import gleam/order.{Eq, Gt, Lt}
 
 pub fn is_between(number: Int, min: Int, and max: Int) {
@@ -9,7 +10,7 @@ pub fn ceil_divide(dividend: Int, by divisor: Int) -> Int {
   { dividend + divisor - 1 } / divisor
 }
 
-fn gcd(a: Int, b: Int) -> Int {
+pub fn gcd(a: Int, b: Int) -> Int {
   case b == 0 {
     True -> a
     False -> gcd(b, a % b)
@@ -22,3 +23,15 @@ pub fn lcm(a: Int, b: Int) -> Int {
     Lt -> { b / gcd(a, b) } * a
   }
 }
+
+fn do_reverse_bits(val: Int, rev: Int, length: Int) -> Int {
+  use <- bool.guard(when: length == 0, return: rev)
+  let lsb = int.bitwise_and(val, 1)
+  let val = int.bitwise_shift_right(val, 1)
+  let rev = int.bitwise_shift_left(rev, 1)
+  do_reverse_bits(val, int.bitwise_or(rev, lsb), length - 1)
+}
+
+pub fn reverse_bits(val: Int, length: Int) -> Int {
+  do_reverse_bits(val, 0, length)
+}