src/catar/encoder.rs: correctly sort goodby items

src/catar/binary_search_tree.rs

@@ -0,0 +1,63 @@
+/// Helpers to generate a binary search tree stored in an array from a
+/// sorted array.
+///
+/// Specifically, for any given sorted * array 'input' permute the
+/// array so that the following rule holds:
+///
+/// For each array item with index i, the item at 2*i+1 is smaller and
+/// the item 2*i+2 is larger.
+///
+/// This structure permits efficient (meaning: O(log(n)) binary
+/// searches: start with item i=0 (i.e. the root of the BST), compare
+/// the value with the searched item, if smaller proceed at item
+/// i*2+1, if larger proceed at item i*2+2, and repeat, until either
+/// the item is found, or the indexes grow beyond the array size,
+/// which means the entry does not exist.
+///
+/// Effectively this implements bisection, but instead of jumping
+/// around wildly in the array during a single search we only search
+/// with strictly monotonically increasing indexes.
+///
+/// Algorithm is from casync (camakebst.c), simplified and optimized
+/// for rust. Permutation function originally by L. Bressel, 2017.
+///
+///
+
+fn copy_binary_search_tree_inner<F:  FnMut(usize, usize)>(
+    copy_func: &mut F,
+    n: usize,
+    o: usize, // Note: virtual offset for input array
+    e: usize,
+    i: usize,
+) {
+    let p = 1 << e;
+
+    let t = p + (p>>1) - 1;
+
+    let m = if n > t {
+        // |...........p.............t....n........(2p)|
+        p - 1
+    } else {
+        // |...........p.....n.......t.............(2p)|
+        p - 1 - (t-n)
+    };
+
+    (copy_func)(o+m, i);
+
+    if m > 0 {
+        copy_binary_search_tree_inner(copy_func, m, 0, e-1, i*2+1);
+    }
+
+    if (m + 1) < n {
+        copy_binary_search_tree_inner(copy_func, n-m-1, o+m+1, e-1, i*2+2);
+    }
+}
+
+pub fn copy_binary_search_tree<F:  FnMut(usize, usize)>(
+    n: usize,
+    mut copy_func: F,
+) {
+    if n == 0 { return };
+    let e = (64 - n.leading_zeros() - 1) as usize; // fast log2(n)
+    copy_binary_search_tree_inner(&mut copy_func, n, 0, e, 0);
+}

src/catar/encoder.rs

@@ -1,6 +1,7 @@
 use failure::*;
 
 use super::format_definition::*;
+use super::binary_search_tree::*;
 
 use std::io::Write;
 use std::os::unix::io::AsRawFd;
@@ -218,7 +219,9 @@ impl <W: Write> CaTarEncoder<W> {
         println!("encode_dir: {:?} end {}", self.current_path, self.writer_pos);
 
         let goodby_start = self.writer_pos as u64;
-        let goodby_table_size = (goodby_items.len() + 1)*std::mem::size_of::<CaFormatGoodbyeItem>();
+
+        let item_count = goodby_items.len();
+        let goodby_table_size = (item_count + 1)*std::mem::size_of::<CaFormatGoodbyeItem>();
 
         for item in &mut goodby_items {
             item.offset = goodby_start - item.offset;
@@ -228,13 +231,6 @@ impl <W: Write> CaTarEncoder<W> {
 
         let goodby_offset = self.writer_pos - dir_start_pos;
 
-        // append CaFormatGoodbyeTail as last item
-        goodby_items.push(CaFormatGoodbyeItem {
-            offset: goodby_offset as u64,
-            size: (goodby_table_size + std::mem::size_of::<CaFormatHeader>()) as u64,
-            hash: CA_FORMAT_GOODBYE_TAIL_MARKER,
-        });
-
         self.write_header(CA_FORMAT_GOODBYE, goodby_table_size as u64)?;
 
         if goodby_table_size > FILE_COPY_BUFFER_SIZE {
@@ -243,13 +239,22 @@ impl <W: Write> CaTarEncoder<W> {
 
         let buffer = &mut self.file_copy_buffer;
         let buffer_ptr = buffer.as_ptr();
-        for (i, item) in goodby_items.iter().enumerate() {
-            unsafe {
-                *(buffer_ptr.add(i*std::mem::size_of::<CaFormatGoodbyeItem>()) as *mut u64) = u64::to_le(item.offset);
-                *(buffer_ptr.add(i*std::mem::size_of::<CaFormatGoodbyeItem>()+8) as *mut u64) = u64::to_le(item.size);
-                *(buffer_ptr.add(i*std::mem::size_of::<CaFormatGoodbyeItem>()+16) as *mut u64) = u64::to_le(item.hash);
-            }
-        }
+
+        copy_binary_search_tree(item_count, |s, d| {
+            let item = &goodby_items[s];
+            let offset = d*std::mem::size_of::<CaFormatGoodbyeItem>();
+            let dest = crate::tools::map_struct_mut::<CaFormatGoodbyeItem>(&mut buffer[offset..]).unwrap();
+            dest.offset = u64::to_le(item.offset);
+            dest.size = u64::to_le(item.size);
+            dest.hash = u64::to_le(item.hash);
+        });
+
+        // append CaFormatGoodbyeTail as last item
+        let offset = item_count*std::mem::size_of::<CaFormatGoodbyeItem>();
+        let dest = crate::tools::map_struct_mut::<CaFormatGoodbyeItem>(&mut buffer[offset..]).unwrap();
+        dest.offset = u64::to_le(goodby_offset as u64);
+        dest.size = u64::to_le((goodby_table_size + std::mem::size_of::<CaFormatHeader>()) as u64);
+        dest.hash = u64::to_le(CA_FORMAT_GOODBYE_TAIL_MARKER);
 
         self.flush_copy_buffer(goodby_table_size)?;
 

src/lib.rs

@@ -32,6 +32,7 @@ pub mod server {
 
 pub mod catar {
 
+    pub mod binary_search_tree;
     pub mod format_definition;
     pub mod encoder;
 }

src/tools.rs

@@ -17,14 +17,14 @@ pub fn map_struct<T>(buffer: &[u8]) -> Result<&T, Error> {
     if buffer.len() < ::std::mem::size_of::<T>() {
         bail!("unable to map struct - buffer too small");
     }
-    return Ok(unsafe { & * (buffer.as_ptr() as *const T) });
+    Ok(unsafe { & * (buffer.as_ptr() as *const T) })
 }
 
 pub fn map_struct_mut<T>(buffer: &mut [u8]) -> Result<&mut T, Error> {
     if buffer.len() < ::std::mem::size_of::<T>() {
         bail!("unable to map struct - buffer too small");
     }
-    return Ok(unsafe { &mut * (buffer.as_ptr() as *mut T) });
+    Ok(unsafe { &mut * (buffer.as_ptr() as *mut T) })
 }