Add dir entry operations

1 files changed, 47 insertions, 3 deletions

diff --git a/src/disk/block.rs b/src/disk/block.rs
index 0058b3e..be3d85a 100644
--- a/src/disk/block.rs
+++ b/src/disk/block.rs
@@ -49,7 +49,7 @@ impl Default for InodeBlock {
 
 impl Block for InodeBlock {}
 
-const FULL_MAP: u32 = 0b111_111_111_111_111;
+const FULL_MAP: u16 = 0b111_111_111_111_111;
 
 #[repr(C)]
 #[derive(Clone)]
@@ -84,7 +84,8 @@ impl Default for DirectoryEntry {
 #[derive(Clone)]
 pub struct DirectoryBlock {
     pub entries: [DirectoryEntry; 15],
-    reserved: [u8; 136],
+    pub occupancy: [u8; 2],
+    reserved: [u8; 134],
 }
 
 impl Default for DirectoryBlock {
@@ -107,7 +108,50 @@ impl Default for DirectoryBlock {
                 DirectoryEntry::default(),
                 DirectoryEntry::default(),
             ],
-            reserved: [0xFF; 136],
+            occupancy: [0x80, 0x00], // 0b1000_0000
+            reserved: [0xFF; 134],
+        }
+    }
+}
+
+impl DirectoryBlock {
+    pub(crate) fn is_full(&self) -> bool {
+        self.occupancy[0] == 0xFF && self.occupancy[1] == 0xFF
+    }
+
+    pub(crate) fn query(&self, mut index: usize) -> bool {
+        if index < 7 { // 0-6, first u8
+            index = index + 1;
+            self.occupancy[0] & (1 << (7 - index)) as u8 != 0
+        } else if index < 15 { // 7-14, second u8
+            index = index - 7;
+            self.occupancy[1] & (1 << (7 - index)) as u8 != 0
+        } else {
+            false
+        }
+    }
+
+    pub(crate) fn allocate(&mut self) -> Option<usize> {
+        if self.occupancy[0] != 0xFF {
+            let leading_ones = self.occupancy[0].leading_ones();
+            self.occupancy[0] |= (1 << (7 - leading_ones)) as u8;
+            Some(leading_ones as usize)
+        } else if self.occupancy[1] != 0xFF {
+            let leading_ones = self.occupancy[1].leading_ones();
+            self.occupancy[1] |= (1 << (7 - leading_ones)) as u8;
+            Some(7 + leading_ones as usize)
+        } else {
+            None
+        }
+    }
+
+    pub(crate) fn deallocate(&mut self, mut index: usize) {
+        if index < 7 {
+            index = index + 1;
+            self.occupancy[0] &= !((1 << (7 - index)) as u8);
+        } else if index < 15 { // 7-14, second u8
+            index = index - 7;
+            self.occupancy[1] &= !((1 << (7 - index)) as u8);
         }
     }
 }