2 files changed, 38 insertions, 0 deletions
diff --git a/src/main.rs b/src/main.rs
index 2b6a814..0dfe335 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,6 +20,25 @@ fn line_offset(
     line: &Rope,
     col: u16,
 ) -> Result<usize, Box<dyn Error>> {
+    let mut n = 0;
+    for i in 0.. {
+        if i == line.len() {
+            return Ok(i);
+        }
+        let c = line.byte(i);
+        if c > 127 {
+            break;
+        }
+        if n == col {
+            return Ok(i);
+        }
+        if c == b'\t' {
+            n += 8 - n % 8;
+        } else {
+            n += 1;
+        }
+    }
+
     // Binary search :D
     let mut lo = 0;
     let mut hi = line.len() + 1;
diff --git a/src/rope.rs b/src/rope.rs
index 31c3296..737d949 100644
--- a/src/rope.rs
+++ b/src/rope.rs
@@ -355,4 +355,23 @@ impl Rope {
             }
         }
     }
+
+    pub fn byte(&self, i: usize) -> u8 {
+        if i >= self.len() {
+            panic!("Index {} out of range 0..{}", i, self.len());
+        }
+        match self {
+            Rope(Node::Leaf(l)) => l.bytes()[i],
+            Rope(Node::Branch(b)) => {
+                let mut i = i;
+                for c in b.children().iter() {
+                    if i < c.len() {
+                        return c.byte(i);
+                    }
+                    i -= c.len();
+                }
+                panic!("unreachable");
+            }
+        }
+    }
 }