Merge pull request #2600 from lavafroth/offset-shortcircuit

refactor: short circuit for known constraints in position lookups

cli/src/parse.rs

@@ -370,10 +370,22 @@ fn parse_edit_flag(source_code: &Vec<u8>, flag: &str) -> Result<Edit> {
     })
 }
 
-fn offset_for_position(input: &Vec<u8>, position: Point) -> usize {
+fn offset_for_position(input: &[u8], position: Point) -> usize {
     let mut current_position = Point { row: 0, column: 0 };
-    for (i, c) in input.iter().enumerate() {
-        if *c as char == '\n' {
+    let mut it = input.iter().enumerate();
+
+    // Skip to where row equals position.row
+    for (_, &c) in &mut it {
+        if c == b'\n' {
+            current_position.row += 1;
+        }
+        if current_position.row == position.row {
+            break;
+        }
+    }
+
+    for (i, &c) in &mut it {
+        if c == b'\n' {
             current_position.row += 1;
             current_position.column = 0;
         } else {
@@ -383,18 +395,21 @@ fn offset_for_position(input: &Vec<u8>, position: Point) -> usize {
             return i;
         }
     }
-    return input.len();
+
+    input.len()
 }
 
-fn position_for_offset(input: &Vec<u8>, offset: usize) -> Point {
+fn position_for_offset(input: &[u8], offset: usize) -> Point {
     let mut result = Point { row: 0, column: 0 };
-    for c in &input[0..offset] {
-        if *c as char == '\n' {
-            result.row += 1;
-            result.column = 0;
-        } else {
+
+    for &c in input[0..offset].iter().rev() {
+        if c != b'\n' && result.row == 0 {
             result.column += 1;
         }
+        if c == b'\n' {
+            result.row += 1;
+        }
     }
+
     result
 }