diff --git a/2025/01/all.rs b/2025/01/all.rs
new file mode 100644
index 0000000..8b69daa
--- /dev/null
+++ b/2025/01/all.rs
@@ -0,0 +1,34 @@
+type SmolI = i32;
+
+#[unsafe(no_mangle)]
+unsafe extern "Rust" fn challenge_isize_duple(buf: &[u8]) -> (isize, isize) {
+    let mut count_p1 = 0;
+    let mut count_p2 = 0;
+    let mut pos = 50;
+
+    let buf = unsafe { str::from_utf8_unchecked(buf.get_unchecked(..(buf.len() - 1))) };
+
+    for ln in buf.split('\n') {
+        let (dir, amt) = unsafe { (*ln.as_bytes().get_unchecked(0), ln.get_unchecked(1..)) };
+
+        let amt: SmolI = unsafe { amt.parse().unwrap_unchecked() };
+        if amt == 0 { continue; }
+        let prev_pos = pos;
+        pos += ((((dir == b'R') as SmolI) << 1) - 1) * amt;
+
+        count_p2 += if pos < 0 {
+            if prev_pos == 0 {
+                count_p2 -= 1;
+            };
+            (pos - 1).div_euclid(100).abs()
+        } else if pos > 0 {
+            pos.div_euclid(100)
+        } else {
+            1
+        };
+        pos = pos.rem_euclid(100);
+        count_p1 += (pos == 0) as SmolI;
+    }
+
+    (count_p1 as isize, count_p2 as isize)
+}
diff --git a/2025/README.md b/2025/README.md
index f98098a..68f684c 100644
--- a/2025/README.md
+++ b/2025/README.md
@@ -1,3 +1,5 @@
 All this year is going to be firstly made in rust, I will do performance too. For that I'ma make a general helper that compiles each rust file into an `.so` file with a common exported main function that takes the input byte buffer and returns a solution (hoping all of them will be integers).
 
 I will make an external rust program that takes the day to run and the input, it will buffer and measure the execution speed.
+
+Performance is critical so we can break behavior with UB for the sake of correct data.
diff --git a/2025/tester.rs b/2025/tester.rs
index 092d4f8..04e8efd 100644
--- a/2025/tester.rs
+++ b/2025/tester.rs
@@ -31,7 +31,11 @@ pub mod dl {
         /// To get the error call [`ffi::error()`].
         pub fn try_drop(self) -> Result<(), (Self, i32)> {
             let err = unsafe { ffi::close(self.0) };
-            if err == 0 { Ok(()) } else { Err((self, err)) }
+            if err == 0 {
+                Ok(())
+            } else {
+                Err((self, err))
+            }
         }
 
         /// # Safety
@@ -176,8 +180,8 @@ pub mod loader {
         // drop.
         untry!(unsafe { handle.symfn::<C<isize>>(c"challenge_isize") }.map(V::Isize));
         untry!(unsafe { handle.symfn::<C<usize>>(c"challenge_isize") }.map(V::Usize));
-        untry!(unsafe { handle.symfn::<C<(usize, usize)>>(c"challenge_isize") }.map(V::UsizeDuple));
-        untry!(unsafe { handle.symfn::<C<(isize, isize)>>(c"challenge_isize") }.map(V::IsizeDuple));
+        untry!(unsafe { handle.symfn::<C<(usize, usize)>>(c"challenge_isize_duple") }.map(V::UsizeDuple));
+        untry!(unsafe { handle.symfn::<C<(isize, isize)>>(c"challenge_isize_duple") }.map(V::IsizeDuple));
 
         None
     }