diff --git a/CHANGELOG.md b/CHANGELOG.md
index 82459e469..2681f6d6f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,17 @@
+Tantivy 0.4.0
+==========================
+
+- Removed u32 fields. They are replaced by u64 and i64 fields (#65)
+- 
+
+
+Tantivy 0.3.1
+==========================
+
+- Expose a method to trigger files garbage collection
+- Raise the limit of number of fields (previously 256 fields)
+
+
 Tantivy 0.3
 ==========================
 
diff --git a/Cargo.toml b/Cargo.toml
index 4316fcbda..274c442b8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "tantivy"
-version = "0.3.1"
+version = "0.4.0-alpha"
 authors = ["Paul Masurel <paul.masurel@gmail.com>"]
 build = "build.rs"
 license = "MIT"
diff --git a/src/core/searcher.rs b/src/core/searcher.rs
index 839e00172..fe54d1a5f 100644
--- a/src/core/searcher.rs
+++ b/src/core/searcher.rs
@@ -68,8 +68,8 @@ impl Searcher {
     }
     
     /// Returns the segment_reader associated with the given segment_ordinal
-    pub fn segment_reader(&self, segment_ord: usize) -> &SegmentReader {
-        &self.segment_readers[segment_ord]
+    pub fn segment_reader(&self, segment_ord: u32) -> &SegmentReader {
+        &self.segment_readers[segment_ord as usize]
     }
        
     /// Runs a query on the segment readers wrapped by the searcher
@@ -78,6 +78,7 @@ impl Searcher {
     }
 }
 
+
 impl From<Vec<SegmentReader>> for Searcher {
     fn from(segment_readers: Vec<SegmentReader>) -> Searcher {
         Searcher {
diff --git a/src/fastfield/error.rs b/src/fastfield/error.rs
index 71497a315..f9f0be0d6 100644
--- a/src/fastfield/error.rs
+++ b/src/fastfield/error.rs
@@ -10,6 +10,10 @@ pub struct FastFieldNotAvailableError {
 }
 
 impl FastFieldNotAvailableError {
+
+    /// Creates a `FastFieldNotAvailable` error.
+    /// `field_entry` is the configuration of the field 
+    /// for which fast fields are not available.
     pub fn new(field_entry: &FieldEntry) -> FastFieldNotAvailableError {
         FastFieldNotAvailableError {
             field_name: field_entry.name().clone(),
diff --git a/src/fastfield/writer.rs b/src/fastfield/writer.rs
index f606b8176..9c85fa146 100644
--- a/src/fastfield/writer.rs
+++ b/src/fastfield/writer.rs
@@ -46,7 +46,7 @@ impl FastFieldsWriter {
             field_writers: field_writers,
         }
     }
-
+    
     pub fn new(fields: Vec<Field>) -> FastFieldsWriter {
         FastFieldsWriter {
             field_writers: fields
@@ -56,6 +56,7 @@ impl FastFieldsWriter {
         }
     }
     
+    /// Get the `FastFieldWriter` associated to a field.
     pub fn get_field_writer(&mut self, field: Field) -> Option<&mut IntFastFieldWriter> {
         // TODO optimize
         self.field_writers
@@ -63,15 +64,19 @@ impl FastFieldsWriter {
             .find(|field_writer| field_writer.field == field)
     }
     
+
+    /// Indexes all of the fastfields of a new document.
     pub fn add_document(&mut self, doc: &Document) {
         for field_writer in &mut self.field_writers {
             field_writer.add_document(doc);
         }
     }
 
+    /// Serializes all of the `FastFieldWriter`s by pushing them in 
+    /// order to the fast field serializer.
     pub fn serialize(&self, serializer: &mut FastFieldSerializer) -> io::Result<()> {
         for field_writer in &self.field_writers {
-            try!(field_writer.serialize(serializer));
+            field_writer.serialize(serializer)?;
         }
         Ok(())
     }
@@ -84,7 +89,6 @@ impl FastFieldsWriter {
         for field_writer in &mut self.field_writers {
             field_writer.fill_val_up_to(doc);
         }
-            
     }
 }
 
@@ -140,7 +144,12 @@ impl IntFastFieldWriter {
             self.add_val(val_if_missing);
         }
     }
-    
+
+    /// Records a new value.
+    ///
+    /// The n-th value being recorded is implicitely
+    /// associated to the document with the `DocId` n.
+    /// (Well, `n-1` actually because of 0-indexing)
     pub fn add_val(&mut self, val: u64) {
         self.vals.push(val);
     }