From 965f378fe84176da3ff2bd40b57fef88f687fbfb Mon Sep 17 00:00:00 2001
From: Malte Kliemann <mail@maltekliemann.com>
Date: Mon, 2 Dec 2024 14:40:21 +0100
Subject: [PATCH] Fix `log_ceil` and add extensive tests

---
 zrml/neo-swaps/src/utility.rs | 39 ++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/zrml/neo-swaps/src/utility.rs b/zrml/neo-swaps/src/utility.rs
index 62103304b..c366c8d1f 100644
--- a/zrml/neo-swaps/src/utility.rs
+++ b/zrml/neo-swaps/src/utility.rs
@@ -16,8 +16,10 @@
 // along with Zeitgeist. If not, see <https://www.gnu.org/licenses/>.
 
 use sp_runtime::SaturatedConversion;
+use sp_runtime::traits::{One, Zero};
 
 pub(crate) trait LogCeil {
+    /// Calculates the ceil of the log with base 2 of `self`.
     fn log_ceil(&self) -> Self;
 }
 
@@ -25,10 +27,45 @@ impl LogCeil for u16 {
     fn log_ceil(&self) -> Self {
         let x = *self;
 
-        let bits_minus_one = u16::MAX.saturating_sub(1);
+        if x.is_zero() {
+            return One::one();
+        }
+
+        let bits_minus_one: u16 = u16::BITS.saturating_sub(1).saturated_into();
         let leading_zeros: u16 = x.leading_zeros().saturated_into();
         let floor_log2 = bits_minus_one.saturating_sub(leading_zeros);
 
         if x.is_power_of_two() { floor_log2 } else { floor_log2.saturating_add(1) }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use test_case::test_case;
+
+    #[test_case(0, 1)]
+    #[test_case(1, 0)]
+    #[test_case(2, 1)]
+    #[test_case(3, 2)]
+    #[test_case(4, 2)]
+    #[test_case(5, 3)]
+    #[test_case(6, 3)]
+    #[test_case(7, 3)]
+    #[test_case(8, 3)]
+    #[test_case(9, 4)]
+    #[test_case(15, 4)]
+    #[test_case(16, 4)]
+    #[test_case(17, 5)]
+    #[test_case(1023, 10)]
+    #[test_case(1024, 10)]
+    #[test_case(1025, 11)]
+    #[test_case(32767, 15)]
+    #[test_case(32768, 15)]
+    #[test_case(32769, 16)]
+    #[test_case(65535, 16)]
+    fn log_ceil_works(value: u16, expected: u16) {
+        let actual = value.log_ceil();
+        assert_eq!(actual, expected);
+    }
+}