Sort directory children in case-agnostic alphabetic order

1 files changed, 37 insertions, 10 deletions

diff --git a/src/devices/file/directory_entry.rs b/src/devices/file/directory_entry.rs
index c4ce146..7f0e69b 100644
--- a/src/devices/file/directory_entry.rs
+++ b/src/devices/file/directory_entry.rs
@@ -10,21 +10,48 @@ pub struct DirectoryChild {
 
 impl PartialOrd for DirectoryChild {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
-        let entry_type_ord = self.entry_type.cmp(&other.entry_type);
-        let final_order = match entry_type_ord {
-            Ordering::Equal => self.byte_path.cmp(&other.byte_path),
-            _ => entry_type_ord,
-        };
-        Some(final_order)
+        Some(self.cmp(other))
     }
 }
 
 impl Ord for DirectoryChild {
     fn cmp(&self, other: &Self) -> Ordering {
-        let entry_type_ord = self.entry_type.cmp(&other.entry_type);
-        match entry_type_ord {
-            Ordering::Equal => self.byte_path.cmp(&other.byte_path),
-            _ => entry_type_ord,
+        match self.entry_type.cmp(&other.entry_type) {
+            Ordering::Equal =>
+                compare_ascii_arrays(&self.byte_path,&other.byte_path),
+            other => other,
         }
     }
 }
+
+// Compare two ASCII arrays in case-agnostic alphabetic order.
+fn compare_ascii_arrays(left: &[u8], right: &[u8]) -> Ordering {
+    let l = std::cmp::min(left.len(), right.len());
+    let lhs = &left[..l];
+    let rhs = &right[..l];
+
+    for i in 0..l {
+        let a = remap_ascii(lhs[i]);
+        let b = remap_ascii(rhs[i]);
+        match a.cmp(&b) {
+            Ordering::Equal => (),
+            non_eq => return non_eq,
+        }
+    }
+
+    left.len().cmp(&right.len())
+}
+
+// Remap ASCII values so that they sort in case-agnostic alphabetic order:
+//    !"#$%&'()*+,-./0123456789:;<=>?
+//   @`AaBbCcDdEeFfGgHhIiJjKkLlMmNnOo
+//   PpQqRrSsTtUuVvWwXxYyZz[{\|]}^~_
+fn remap_ascii(c: u8) -> u8 {
+    if 0x40 <= c && c <= 0x5F {
+        (c - 0x40) * 2 + 0x40
+    } else if 0x60 <= c && c <= 0x7F {
+        (c - 0x60) * 2 + 0x41
+    } else {
+        c
+    }
+}