pull extra::{serialize, ebml} into a separate libserialize crate

- `extra::json` didn't make the cut, because of `extra::json` required
   dep on `extra::TreeMap`. If/when `extra::TreeMap` moves out of `extra`,
   then `extra::json` could move into `serialize`
- `libextra`, `libsyntax` and `librustc` depend on the newly created
  `libserialize`
- The extensions to various `extra` types like `DList`, `RingBuf`, `TreeMap`
  and `TreeSet` for `Encodable`/`Decodable` were moved into the respective
  modules in `extra`
- There is some trickery, evident in `src/libextra/lib.rs` where a stub
  of `extra::serialize` is set up (in `src/libextra/serialize.rs`) for
  use in the stage0 build, where the snapshot rustc is still making
  deriving for `Encodable` and `Decodable` point at extra. Big props to
  @huonw for help working out the re-export solution for this

extra: inline extra::serialize stub

fix stuff clobbered in rebase + don't reexport serialize::serialize

no more globs in libserialize

syntax: fix import of libserialize traits

librustc: fix bad imports in encoder/decoder

add serialize dep to librustdoc

fix failing run-pass tests w/ serialize dep

adjust uuid dep

more rebase de-clobbering for libserialize

fixing tests, pushing libextra dep into cfg(test)

fix doc code in extra::json

adjust index.md links to serialize and uuid library

1 files changed, 1121 insertions, 0 deletions

diff --git a/src/libserialize/ebml.rs b/src/libserialize/ebml.rs
new file mode 100644
index 00000000000..9d1c099c6f0
--- /dev/null
+++ b/src/libserialize/ebml.rs
@@ -0,0 +1,1121 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[allow(missing_doc)];
+
+use std::str;
+
+macro_rules! if_ok( ($e:expr) => (
+    match $e { Ok(e) => e, Err(e) => { self.last_error = Err(e); return } }
+) )
+
+// Simple Extensible Binary Markup Language (ebml) reader and writer on a
+// cursor model. See the specification here:
+//     http://www.matroska.org/technical/specs/rfc/index.html
+
+// Common data structures
+#[deriving(Clone)]
+pub struct Doc<'a> {
+    data: &'a [u8],
+    start: uint,
+    end: uint,
+}
+
+impl<'doc> Doc<'doc> {
+    pub fn get<'a>(&'a self, tag: uint) -> Doc<'a> {
+        reader::get_doc(*self, tag)
+    }
+
+    pub fn as_str_slice<'a>(&'a self) -> &'a str {
+        str::from_utf8(self.data.slice(self.start, self.end)).unwrap()
+    }
+
+    pub fn as_str(&self) -> ~str {
+        self.as_str_slice().to_owned()
+    }
+}
+
+pub struct TaggedDoc<'a> {
+    priv tag: uint,
+    doc: Doc<'a>,
+}
+
+pub enum EbmlEncoderTag {
+    EsUint,     // 0
+    EsU64,      // 1
+    EsU32,      // 2
+    EsU16,      // 3
+    EsU8,       // 4
+    EsInt,      // 5
+    EsI64,      // 6
+    EsI32,      // 7
+    EsI16,      // 8
+    EsI8,       // 9
+    EsBool,     // 10
+    EsChar,     // 11
+    EsStr,      // 12
+    EsF64,      // 13
+    EsF32,      // 14
+    EsFloat,    // 15
+    EsEnum,     // 16
+    EsEnumVid,  // 17
+    EsEnumBody, // 18
+    EsVec,      // 19
+    EsVecLen,   // 20
+    EsVecElt,   // 21
+    EsMap,      // 22
+    EsMapLen,   // 23
+    EsMapKey,   // 24
+    EsMapVal,   // 25
+
+    EsOpaque,
+
+    EsLabel, // Used only when debugging
+}
+// --------------------------------------
+
+pub mod reader {
+    use std::char;
+
+    use std::cast::transmute;
+    use std::int;
+    use std::option::{None, Option, Some};
+    use std::io::extensions::u64_from_be_bytes;
+
+    use serialize;
+
+    use super::{ EsVec, EsMap, EsEnum, EsVecLen, EsVecElt, EsMapLen, EsMapKey,
+        EsEnumVid, EsU64, EsU32, EsU16, EsU8, EsInt, EsI64, EsI32, EsI16, EsI8,
+        EsBool, EsF64, EsF32, EsChar, EsStr, EsMapVal, EsEnumBody, EsUint,
+        EsOpaque, EsLabel, EbmlEncoderTag, Doc, TaggedDoc };
+
+    // ebml reading
+
+    pub struct Res {
+        val: uint,
+        next: uint
+    }
+
+    #[inline(never)]
+    fn vuint_at_slow(data: &[u8], start: uint) -> Res {
+        let a = data[start];
+        if a & 0x80u8 != 0u8 {
+            return Res {val: (a & 0x7fu8) as uint, next: start + 1u};
+        }
+        if a & 0x40u8 != 0u8 {
+            return Res {val: ((a & 0x3fu8) as uint) << 8u |
+                        (data[start + 1u] as uint),
+                    next: start + 2u};
+        }
+        if a & 0x20u8 != 0u8 {
+            return Res {val: ((a & 0x1fu8) as uint) << 16u |
+                        (data[start + 1u] as uint) << 8u |
+                        (data[start + 2u] as uint),
+                    next: start + 3u};
+        }
+        if a & 0x10u8 != 0u8 {
+            return Res {val: ((a & 0x0fu8) as uint) << 24u |
+                        (data[start + 1u] as uint) << 16u |
+                        (data[start + 2u] as uint) << 8u |
+                        (data[start + 3u] as uint),
+                    next: start + 4u};
+        }
+        fail!("vint too big");
+    }
+
+    pub fn vuint_at(data: &[u8], start: uint) -> Res {
+        use std::ptr::offset;
+        use std::unstable::intrinsics::from_be32;
+
+        if data.len() - start < 4 {
+            return vuint_at_slow(data, start);
+        }
+
+        // Lookup table for parsing EBML Element IDs as per http://ebml.sourceforge.net/specs/
+        // The Element IDs are parsed by reading a big endian u32 positioned at data[start].
+        // Using the four most significant bits of the u32 we lookup in the table below how the
+        // element ID should be derived from it.
+        //
+        // The table stores tuples (shift, mask) where shift is the number the u32 should be right
+        // shifted with and mask is the value the right shifted value should be masked with.
+        // If for example the most significant bit is set this means it's a class A ID and the u32
+        // should be right shifted with 24 and masked with 0x7f. Therefore we store (24, 0x7f) at
+        // index 0x8 - 0xF (four bit numbers where the most significant bit is set).
+        //
+        // By storing the number of shifts and masks in a table instead of checking in order if
+        // the most significant bit is set, the second most significant bit is set etc. we can
+        // replace up to three "and+branch" with a single table lookup which gives us a measured
+        // speedup of around 2x on x86_64.
+        static SHIFT_MASK_TABLE: [(u32, u32), ..16] = [
+            (0, 0x0), (0, 0x0fffffff),
+            (8, 0x1fffff), (8, 0x1fffff),
+            (16, 0x3fff), (16, 0x3fff), (16, 0x3fff), (16, 0x3fff),
+            (24, 0x7f), (24, 0x7f), (24, 0x7f), (24, 0x7f),
+            (24, 0x7f), (24, 0x7f), (24, 0x7f), (24, 0x7f)
+        ];
+
+        unsafe {
+            let (ptr, _): (*u8, uint) = transmute(data);
+            let ptr = offset(ptr, start as int);
+            let ptr: *i32 = transmute(ptr);
+            let val = from_be32(*ptr) as u32;
+
+            let i = (val >> 28u) as uint;
+            let (shift, mask) = SHIFT_MASK_TABLE[i];
+            Res {
+                val: ((val >> shift) & mask) as uint,
+                next: start + (((32 - shift) >> 3) as uint)
+            }
+        }
+    }
+
+    pub fn Doc<'a>(data: &'a [u8]) -> Doc<'a> {
+        Doc { data: data, start: 0u, end: data.len() }
+    }
+
+    pub fn doc_at<'a>(data: &'a [u8], start: uint) -> TaggedDoc<'a> {
+        let elt_tag = vuint_at(data, start);
+        let elt_size = vuint_at(data, elt_tag.next);
+        let end = elt_size.next + elt_size.val;
+        TaggedDoc {
+            tag: elt_tag.val,
+            doc: Doc { data: data, start: elt_size.next, end: end }
+        }
+    }
+
+    pub fn maybe_get_doc<'a>(d: Doc<'a>, tg: uint) -> Option<Doc<'a>> {
+        let mut pos = d.start;
+        while pos < d.end {
+            let elt_tag = vuint_at(d.data, pos);
+            let elt_size = vuint_at(d.data, elt_tag.next);
+            pos = elt_size.next + elt_size.val;
+            if elt_tag.val == tg {
+                return Some(Doc { data: d.data, start: elt_size.next,
+                                  end: pos });
+            }
+        }
+        None
+    }
+
+    pub fn get_doc<'a>(d: Doc<'a>, tg: uint) -> Doc<'a> {
+        match maybe_get_doc(d, tg) {
+            Some(d) => d,
+            None => {
+                error!("failed to find block with tag {}", tg);
+                fail!();
+            }
+        }
+    }
+
+    pub fn docs<'a>(d: Doc<'a>, it: |uint, Doc<'a>| -> bool) -> bool {
+        let mut pos = d.start;
+        while pos < d.end {
+            let elt_tag = vuint_at(d.data, pos);
+            let elt_size = vuint_at(d.data, elt_tag.next);
+            pos = elt_size.next + elt_size.val;
+            let doc = Doc { data: d.data, start: elt_size.next, end: pos };
+            if !it(elt_tag.val, doc) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    pub fn tagged_docs<'a>(d: Doc<'a>, tg: uint, it: |Doc<'a>| -> bool) -> bool {
+        let mut pos = d.start;
+        while pos < d.end {
+            let elt_tag = vuint_at(d.data, pos);
+            let elt_size = vuint_at(d.data, elt_tag.next);
+            pos = elt_size.next + elt_size.val;
+            if elt_tag.val == tg {
+                let doc = Doc { data: d.data, start: elt_size.next,
+                                end: pos };
+                if !it(doc) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    pub fn with_doc_data<'a, T>(d: Doc<'a>, f: |x: &'a [u8]| -> T) -> T {
+        f(d.data.slice(d.start, d.end))
+    }
+
+
+    pub fn doc_as_u8(d: Doc) -> u8 {
+        assert_eq!(d.end, d.start + 1u);
+        d.data[d.start]
+    }
+
+    pub fn doc_as_u16(d: Doc) -> u16 {
+        assert_eq!(d.end, d.start + 2u);
+        u64_from_be_bytes(d.data, d.start, 2u) as u16
+    }
+
+    pub fn doc_as_u32(d: Doc) -> u32 {
+        assert_eq!(d.end, d.start + 4u);
+        u64_from_be_bytes(d.data, d.start, 4u) as u32
+    }
+
+    pub fn doc_as_u64(d: Doc) -> u64 {
+        assert_eq!(d.end, d.start + 8u);
+        u64_from_be_bytes(d.data, d.start, 8u)
+    }
+
+    pub fn doc_as_i8(d: Doc) -> i8 { doc_as_u8(d) as i8 }
+    pub fn doc_as_i16(d: Doc) -> i16 { doc_as_u16(d) as i16 }
+    pub fn doc_as_i32(d: Doc) -> i32 { doc_as_u32(d) as i32 }
+    pub fn doc_as_i64(d: Doc) -> i64 { doc_as_u64(d) as i64 }
+
+    pub struct Decoder<'a> {
+        priv parent: Doc<'a>,
+        priv pos: uint,
+    }
+
+    pub fn Decoder<'a>(d: Doc<'a>) -> Decoder<'a> {
+        Decoder {
+            parent: d,
+            pos: d.start
+        }
+    }
+
+    impl<'doc> Decoder<'doc> {
+        fn _check_label(&mut self, lbl: &str) {
+            if self.pos < self.parent.end {
+                let TaggedDoc { tag: r_tag, doc: r_doc } =
+                    doc_at(self.parent.data, self.pos);
+
+                if r_tag == (EsLabel as uint) {
+                    self.pos = r_doc.end;
+                    let str = r_doc.as_str_slice();
+                    if lbl != str {
+                        fail!("Expected label {} but found {}", lbl, str);
+                    }
+                }
+            }
+        }
+
+        fn next_doc(&mut self, exp_tag: EbmlEncoderTag) -> Doc<'doc> {
+            debug!(". next_doc(exp_tag={:?})", exp_tag);
+            if self.pos >= self.parent.end {
+                fail!("no more documents in current node!");
+            }
+            let TaggedDoc { tag: r_tag, doc: r_doc } =
+                doc_at(self.parent.data, self.pos);
+            debug!("self.parent={}-{} self.pos={} r_tag={} r_doc={}-{}",
+                   self.parent.start,
+                   self.parent.end,
+                   self.pos,
+                   r_tag,
+                   r_doc.start,
+                   r_doc.end);
+            if r_tag != (exp_tag as uint) {
+                fail!("expected EBML doc with tag {:?} but found tag {:?}",
+                       exp_tag, r_tag);
+            }
+            if r_doc.end > self.parent.end {
+                fail!("invalid EBML, child extends to {:#x}, parent to {:#x}",
+                      r_doc.end, self.parent.end);
+            }
+            self.pos = r_doc.end;
+            r_doc
+        }
+
+        fn push_doc<T>(&mut self, exp_tag: EbmlEncoderTag,
+                       f: |&mut Decoder<'doc>| -> T) -> T {
+            let d = self.next_doc(exp_tag);
+            let old_parent = self.parent;
+            let old_pos = self.pos;
+            self.parent = d;
+            self.pos = d.start;
+            let r = f(self);
+            self.parent = old_parent;
+            self.pos = old_pos;
+            r
+        }
+
+        fn _next_uint(&mut self, exp_tag: EbmlEncoderTag) -> uint {
+            let r = doc_as_u32(self.next_doc(exp_tag));
+            debug!("_next_uint exp_tag={:?} result={}", exp_tag, r);
+            r as uint
+        }
+
+        pub fn read_opaque<R>(&mut self, op: |&mut Decoder<'doc>, Doc| -> R) -> R {
+            let doc = self.next_doc(EsOpaque);
+
+            let (old_parent, old_pos) = (self.parent, self.pos);
+            self.parent = doc;
+            self.pos = doc.start;
+
+            let result = op(self, doc);
+
+            self.parent = old_parent;
+            self.pos = old_pos;
+            result
+        }
+    }
+
+    impl<'doc> serialize::Decoder for Decoder<'doc> {
+        fn read_nil(&mut self) -> () { () }
+
+        fn read_u64(&mut self) -> u64 { doc_as_u64(self.next_doc(EsU64)) }
+        fn read_u32(&mut self) -> u32 { doc_as_u32(self.next_doc(EsU32)) }
+        fn read_u16(&mut self) -> u16 { doc_as_u16(self.next_doc(EsU16)) }
+        fn read_u8 (&mut self) -> u8  { doc_as_u8 (self.next_doc(EsU8 )) }
+        fn read_uint(&mut self) -> uint {
+            let v = doc_as_u64(self.next_doc(EsUint));
+            if v > (::std::uint::MAX as u64) {
+                fail!("uint {} too large for this architecture", v);
+            }
+            v as uint
+        }
+
+        fn read_i64(&mut self) -> i64 {
+            doc_as_u64(self.next_doc(EsI64)) as i64
+        }
+        fn read_i32(&mut self) -> i32 {
+            doc_as_u32(self.next_doc(EsI32)) as i32
+        }
+        fn read_i16(&mut self) -> i16 {
+            doc_as_u16(self.next_doc(EsI16)) as i16
+        }
+        fn read_i8 (&mut self) -> i8 {
+            doc_as_u8(self.next_doc(EsI8 )) as i8
+        }
+        fn read_int(&mut self) -> int {
+            let v = doc_as_u64(self.next_doc(EsInt)) as i64;
+            if v > (int::MAX as i64) || v < (int::MIN as i64) {
+                debug!("FIXME \\#6122: Removing this makes this function miscompile");
+                fail!("int {} out of range for this architecture", v);
+            }
+            v as int
+        }
+
+        fn read_bool(&mut self) -> bool {
+            doc_as_u8(self.next_doc(EsBool)) != 0
+        }
+
+        fn read_f64(&mut self) -> f64 {
+            let bits = doc_as_u64(self.next_doc(EsF64));
+            unsafe { transmute(bits) }
+        }
+        fn read_f32(&mut self) -> f32 {
+            let bits = doc_as_u32(self.next_doc(EsF32));
+            unsafe { transmute(bits) }
+        }
+        fn read_char(&mut self) -> char {
+            char::from_u32(doc_as_u32(self.next_doc(EsChar))).unwrap()
+        }
+        fn read_str(&mut self) -> ~str {
+            self.next_doc(EsStr).as_str()
+        }
+
+        // Compound types:
+        fn read_enum<T>(&mut self, name: &str, f: |&mut Decoder<'doc>| -> T) -> T {
+            debug!("read_enum({})", name);
+            self._check_label(name);
+
+            let doc = self.next_doc(EsEnum);
+
+            let (old_parent, old_pos) = (self.parent, self.pos);
+            self.parent = doc;
+            self.pos = self.parent.start;
+
+            let result = f(self);
+
+            self.parent = old_parent;
+            self.pos = old_pos;
+            result
+        }
+
+        fn read_enum_variant<T>(&mut self,
+                                _: &[&str],
+                                f: |&mut Decoder<'doc>, uint| -> T)
+                                -> T {
+            debug!("read_enum_variant()");
+            let idx = self._next_uint(EsEnumVid);
+            debug!("  idx={}", idx);
+
+            let doc = self.next_doc(EsEnumBody);
+
+            let (old_parent, old_pos) = (self.parent, self.pos);
+            self.parent = doc;
+            self.pos = self.parent.start;
+
+            let result = f(self, idx);
+
+            self.parent = old_parent;
+            self.pos = old_pos;
+            result
+        }
+
+        fn read_enum_variant_arg<T>(&mut self,
+                                    idx: uint,
+                                    f: |&mut Decoder<'doc>| -> T) -> T {
+            debug!("read_enum_variant_arg(idx={})", idx);
+            f(self)
+        }
+
+        fn read_enum_struct_variant<T>(&mut self,
+                                       _: &[&str],
+                                       f: |&mut Decoder<'doc>, uint| -> T)
+                                       -> T {
+            debug!("read_enum_struct_variant()");
+            let idx = self._next_uint(EsEnumVid);
+            debug!("  idx={}", idx);
+
+            let doc = self.next_doc(EsEnumBody);
+
+            let (old_parent, old_pos) = (self.parent, self.pos);
+            self.parent = doc;
+            self.pos = self.parent.start;
+
+            let result = f(self, idx);
+
+            self.parent = old_parent;
+            self.pos = old_pos;
+            result
+        }
+
+        fn read_enum_struct_variant_field<T>(&mut self,
+                                             name: &str,
+                                             idx: uint,
+                                             f: |&mut Decoder<'doc>| -> T)
+                                             -> T {
+            debug!("read_enum_struct_variant_arg(name={}, idx={})", name, idx);
+            f(self)
+        }
+
+        fn read_struct<T>(&mut self,
+                          name: &str,
+                          _: uint,
+                          f: |&mut Decoder<'doc>| -> T)
+                          -> T {
+            debug!("read_struct(name={})", name);
+            f(self)
+        }
+
+        fn read_struct_field<T>(&mut self,
+                                name: &str,
+                                idx: uint,
+                                f: |&mut Decoder<'doc>| -> T)
+                                -> T {
+            debug!("read_struct_field(name={}, idx={})", name, idx);
+            self._check_label(name);
+            f(self)
+        }
+
+        fn read_tuple<T>(&mut self, f: |&mut Decoder<'doc>, uint| -> T) -> T {
+            debug!("read_tuple()");
+            self.read_seq(f)
+        }
+
+        fn read_tuple_arg<T>(&mut self, idx: uint, f: |&mut Decoder<'doc>| -> T)
+                             -> T {
+            debug!("read_tuple_arg(idx={})", idx);
+            self.read_seq_elt(idx, f)
+        }
+
+        fn read_tuple_struct<T>(&mut self,
+                                name: &str,
+                                f: |&mut Decoder<'doc>, uint| -> T)
+                                -> T {
+            debug!("read_tuple_struct(name={})", name);
+            self.read_tuple(f)
+        }
+
+        fn read_tuple_struct_arg<T>(&mut self,
+                                    idx: uint,
+                                    f: |&mut Decoder<'doc>| -> T)
+                                    -> T {
+            debug!("read_tuple_struct_arg(idx={})", idx);
+            self.read_tuple_arg(idx, f)
+        }
+
+        fn read_option<T>(&mut self, f: |&mut Decoder<'doc>, bool| -> T) -> T {
+            debug!("read_option()");
+            self.read_enum("Option", |this| {
+                this.read_enum_variant(["None", "Some"], |this, idx| {
+                    match idx {
+                        0 => f(this, false),
+                        1 => f(this, true),
+                        _ => fail!(),
+                    }
+                })
+            })
+        }
+
+        fn read_seq<T>(&mut self, f: |&mut Decoder<'doc>, uint| -> T) -> T {
+            debug!("read_seq()");
+            self.push_doc(EsVec, |d| {
+                let len = d._next_uint(EsVecLen);
+                debug!("  len={}", len);
+                f(d, len)
+            })
+        }
+
+        fn read_seq_elt<T>(&mut self, idx: uint, f: |&mut Decoder<'doc>| -> T)
+                           -> T {
+            debug!("read_seq_elt(idx={})", idx);
+            self.push_doc(EsVecElt, f)
+        }
+
+        fn read_map<T>(&mut self, f: |&mut Decoder<'doc>, uint| -> T) -> T {
+            debug!("read_map()");
+            self.push_doc(EsMap, |d| {
+                let len = d._next_uint(EsMapLen);
+                debug!("  len={}", len);
+                f(d, len)
+            })
+        }
+
+        fn read_map_elt_key<T>(&mut self, idx: uint, f: |&mut Decoder<'doc>| -> T)
+                               -> T {
+            debug!("read_map_elt_key(idx={})", idx);
+            self.push_doc(EsMapKey, f)
+        }
+
+        fn read_map_elt_val<T>(&mut self, idx: uint, f: |&mut Decoder<'doc>| -> T)
+                               -> T {
+            debug!("read_map_elt_val(idx={})", idx);
+            self.push_doc(EsMapVal, f)
+        }
+    }
+}
+
+pub mod writer {
+    use std::cast;
+    use std::clone::Clone;
+    use std::io;
+    use std::io::{Writer, Seek};
+    use std::io::MemWriter;
+    use std::io::extensions::u64_to_be_bytes;
+
+    use super::{ EsVec, EsMap, EsEnum, EsVecLen, EsVecElt, EsMapLen, EsMapKey,
+        EsEnumVid, EsU64, EsU32, EsU16, EsU8, EsInt, EsI64, EsI32, EsI16, EsI8,
+        EsBool, EsF64, EsF32, EsChar, EsStr, EsMapVal, EsEnumBody, EsUint,
+        EsOpaque, EsLabel, EbmlEncoderTag };
+
+    use serialize;
+
+    // ebml writing
+    pub struct Encoder<'a> {
+        // FIXME(#5665): this should take a trait object. Note that if you
+        //               delete this comment you should consider removing the
+        //               unwrap()'s below of the results of the calls to
+        //               write(). We're guaranteed that writing into a MemWriter
+        //               won't fail, but this is not true for all I/O streams in
+        //               general.
+        writer: &'a mut MemWriter,
+        priv size_positions: ~[uint],
+        last_error: io::IoResult<()>,
+    }
+
+    fn write_sized_vuint(w: &mut MemWriter, n: uint, size: uint) {
+        match size {
+            1u => w.write(&[0x80u8 | (n as u8)]),
+            2u => w.write(&[0x40u8 | ((n >> 8_u) as u8), n as u8]),
+            3u => w.write(&[0x20u8 | ((n >> 16_u) as u8), (n >> 8_u) as u8,
+                            n as u8]),
+            4u => w.write(&[0x10u8 | ((n >> 24_u) as u8), (n >> 16_u) as u8,
+                            (n >> 8_u) as u8, n as u8]),
+            _ => fail!("vint to write too big: {}", n)
+        }.unwrap()
+    }
+
+    fn write_vuint(w: &mut MemWriter, n: uint) {
+        if n < 0x7f_u { write_sized_vuint(w, n, 1u); return; }
+        if n < 0x4000_u { write_sized_vuint(w, n, 2u); return; }
+        if n < 0x200000_u { write_sized_vuint(w, n, 3u); return; }
+        if n < 0x10000000_u { write_sized_vuint(w, n, 4u); return; }
+        fail!("vint to write too big: {}", n);
+    }
+
+    pub fn Encoder<'a>(w: &'a mut MemWriter) -> Encoder<'a> {
+        let size_positions: ~[uint] = ~[];
+        Encoder {
+            writer: w,
+            size_positions: size_positions,
+            last_error: Ok(()),
+        }
+    }
+
+    // FIXME (#2741): Provide a function to write the standard ebml header.
+    impl<'a> Encoder<'a> {
+        /// FIXME(pcwalton): Workaround for badness in trans. DO NOT USE ME.
+        pub unsafe fn unsafe_clone(&self) -> Encoder<'a> {
+            Encoder {
+                writer: cast::transmute_copy(&self.writer),
+                size_positions: self.size_positions.clone(),
+                last_error: Ok(()),
+            }
+        }
+
+        pub fn start_tag(&mut self, tag_id: uint) {
+            debug!("Start tag {}", tag_id);
+
+            // Write the enum ID:
+            write_vuint(self.writer, tag_id);
+
+            // Write a placeholder four-byte size.
+            self.size_positions.push(if_ok!(self.writer.tell()) as uint);
+            let zeroes: &[u8] = &[0u8, 0u8, 0u8, 0u8];
+            if_ok!(self.writer.write(zeroes));
+        }
+
+        pub fn end_tag(&mut self) {
+            let last_size_pos = self.size_positions.pop().unwrap();
+            let cur_pos = if_ok!(self.writer.tell());
+            if_ok!(self.writer.seek(last_size_pos as i64, io::SeekSet));
+            let size = (cur_pos as uint - last_size_pos - 4);
+            write_sized_vuint(self.writer, size, 4u);
+            if_ok!(self.writer.seek(cur_pos as i64, io::SeekSet));
+
+            debug!("End tag (size = {})", size);
+        }
+
+        pub fn wr_tag(&mut self, tag_id: uint, blk: ||) {
+            self.start_tag(tag_id);
+            blk();
+            self.end_tag();
+        }
+
+        pub fn wr_tagged_bytes(&mut self, tag_id: uint, b: &[u8]) {
+            write_vuint(self.writer, tag_id);
+            write_vuint(self.writer, b.len());
+            self.writer.write(b).unwrap();
+        }
+
+        pub fn wr_tagged_u64(&mut self, tag_id: uint, v: u64) {
+            u64_to_be_bytes(v, 8u, |v| {
+                self.wr_tagged_bytes(tag_id, v);
+            })
+        }
+
+        pub fn wr_tagged_u32(&mut self, tag_id: uint, v: u32) {
+            u64_to_be_bytes(v as u64, 4u, |v| {
+                self.wr_tagged_bytes(tag_id, v);
+            })
+        }
+
+        pub fn wr_tagged_u16(&mut self, tag_id: uint, v: u16) {
+            u64_to_be_bytes(v as u64, 2u, |v| {
+                self.wr_tagged_bytes(tag_id, v);
+            })
+        }
+
+        pub fn wr_tagged_u8(&mut self, tag_id: uint, v: u8) {
+            self.wr_tagged_bytes(tag_id, &[v]);
+        }
+
+        pub fn wr_tagged_i64(&mut self, tag_id: uint, v: i64) {
+            u64_to_be_bytes(v as u64, 8u, |v| {
+                self.wr_tagged_bytes(tag_id, v);
+            })
+        }
+
+        pub fn wr_tagged_i32(&mut self, tag_id: uint, v: i32) {
+            u64_to_be_bytes(v as u64, 4u, |v| {
+                self.wr_tagged_bytes(tag_id, v);
+            })
+        }
+
+        pub fn wr_tagged_i16(&mut self, tag_id: uint, v: i16) {
+            u64_to_be_bytes(v as u64, 2u, |v| {
+                self.wr_tagged_bytes(tag_id, v);
+            })
+        }
+
+        pub fn wr_tagged_i8(&mut self, tag_id: uint, v: i8) {
+            self.wr_tagged_bytes(tag_id, &[v as u8]);
+        }
+
+        pub fn wr_tagged_str(&mut self, tag_id: uint, v: &str) {
+            self.wr_tagged_bytes(tag_id, v.as_bytes());
+        }
+
+        pub fn wr_bytes(&mut self, b: &[u8]) {
+            debug!("Write {} bytes", b.len());
+            self.writer.write(b).unwrap();
+        }
+
+        pub fn wr_str(&mut self, s: &str) {
+            debug!("Write str: {}", s);
+            self.writer.write(s.as_bytes()).unwrap();
+        }
+    }
+
+    // FIXME (#2743): optionally perform "relaxations" on end_tag to more
+    // efficiently encode sizes; this is a fixed point iteration
+
+    // Set to true to generate more debugging in EBML code.
+    // Totally lame approach.
+    static DEBUG: bool = true;
+
+    impl<'a> Encoder<'a> {
+        // used internally to emit things like the vector length and so on
+        fn _emit_tagged_uint(&mut self, t: EbmlEncoderTag, v: uint) {
+            assert!(v <= 0xFFFF_FFFF_u);
+            self.wr_tagged_u32(t as uint, v as u32);
+        }
+
+        fn _emit_label(&mut self, label: &str) {
+            // There are various strings that we have access to, such as
+            // the name of a record field, which do not actually appear in
+            // the encoded EBML (normally).  This is just for
+            // efficiency.  When debugging, though, we can emit such
+            // labels and then they will be checked by decoder to
+            // try and check failures more quickly.
+            if DEBUG { self.wr_tagged_str(EsLabel as uint, label) }
+        }
+
+        pub fn emit_opaque(&mut self, f: |&mut Encoder|) {
+            self.start_tag(EsOpaque as uint);
+            f(self);
+            self.end_tag();
+        }
+    }
+
+    impl<'a> serialize::Encoder for Encoder<'a> {
+        fn emit_nil(&mut self) {}
+
+        fn emit_uint(&mut self, v: uint) {
+            self.wr_tagged_u64(EsUint as uint, v as u64);
+        }
+        fn emit_u64(&mut self, v: u64) {
+            self.wr_tagged_u64(EsU64 as uint, v);
+        }
+        fn emit_u32(&mut self, v: u32) {
+            self.wr_tagged_u32(EsU32 as uint, v);
+        }
+        fn emit_u16(&mut self, v: u16) {
+            self.wr_tagged_u16(EsU16 as uint, v);
+        }
+        fn emit_u8(&mut self, v: u8) {
+            self.wr_tagged_u8(EsU8 as uint, v);
+        }
+
+        fn emit_int(&mut self, v: int) {
+            self.wr_tagged_i64(EsInt as uint, v as i64);
+        }
+        fn emit_i64(&mut self, v: i64) {
+            self.wr_tagged_i64(EsI64 as uint, v);
+        }
+        fn emit_i32(&mut self, v: i32) {
+            self.wr_tagged_i32(EsI32 as uint, v);
+        }
+        fn emit_i16(&mut self, v: i16) {
+            self.wr_tagged_i16(EsI16 as uint, v);
+        }
+        fn emit_i8(&mut self, v: i8) {
+            self.wr_tagged_i8(EsI8 as uint, v);
+        }
+
+        fn emit_bool(&mut self, v: bool) {
+            self.wr_tagged_u8(EsBool as uint, v as u8)
+        }
+
+        fn emit_f64(&mut self, v: f64) {
+            let bits = unsafe { cast::transmute(v) };
+            self.wr_tagged_u64(EsF64 as uint, bits);
+        }
+        fn emit_f32(&mut self, v: f32) {
+            let bits = unsafe { cast::transmute(v) };
+            self.wr_tagged_u32(EsF32 as uint, bits);
+        }
+        fn emit_char(&mut self, v: char) {
+            self.wr_tagged_u32(EsChar as uint, v as u32);
+        }
+
+        fn emit_str(&mut self, v: &str) {
+            self.wr_tagged_str(EsStr as uint, v)
+        }
+
+        fn emit_enum(&mut self, name: &str, f: |&mut Encoder<'a>|) {
+            self._emit_label(name);
+            self.start_tag(EsEnum as uint);
+            f(self);
+            self.end_tag();
+        }
+
+        fn emit_enum_variant(&mut self,
+                             _: &str,
+                             v_id: uint,
+                             _: uint,
+                             f: |&mut Encoder<'a>|) {
+            self._emit_tagged_uint(EsEnumVid, v_id);
+            self.start_tag(EsEnumBody as uint);
+            f(self);
+            self.end_tag();
+        }
+
+        fn emit_enum_variant_arg(&mut self, _: uint, f: |&mut Encoder<'a>|) {
+            f(self)
+        }
+
+        fn emit_enum_struct_variant(&mut self,
+                                    v_name: &str,
+                                    v_id: uint,
+                                    cnt: uint,
+                                    f: |&mut Encoder<'a>|) {
+            self.emit_enum_variant(v_name, v_id, cnt, f)
+        }
+
+        fn emit_enum_struct_variant_field(&mut self,
+                                          _: &str,
+                                          idx: uint,
+                                          f: |&mut Encoder<'a>|) {
+            self.emit_enum_variant_arg(idx, f)
+        }
+
+        fn emit_struct(&mut self,
+                       _: &str,
+                       _len: uint,
+                       f: |&mut Encoder<'a>|) {
+            f(self)
+        }
+
+        fn emit_struct_field(&mut self,
+                             name: &str,
+                             _: uint,
+                             f: |&mut Encoder<'a>|) {
+            self._emit_label(name);
+            f(self)
+        }
+
+        fn emit_tuple(&mut self, len: uint, f: |&mut Encoder<'a>|) {
+            self.emit_seq(len, f)
+        }
+        fn emit_tuple_arg(&mut self, idx: uint, f: |&mut Encoder<'a>|) {
+            self.emit_seq_elt(idx, f)
+        }
+
+        fn emit_tuple_struct(&mut self,
+                             _: &str,
+                             len: uint,
+                             f: |&mut Encoder<'a>|) {
+            self.emit_seq(len, f)
+        }
+        fn emit_tuple_struct_arg(&mut self,
+                                 idx: uint,
+                                 f: |&mut Encoder<'a>|) {
+            self.emit_seq_elt(idx, f)
+        }
+
+        fn emit_option(&mut self, f: |&mut Encoder<'a>|) {
+            self.emit_enum("Option", f);
+        }
+        fn emit_option_none(&mut self) {
+            self.emit_enum_variant("None", 0, 0, |_| ())
+        }
+        fn emit_option_some(&mut self, f: |&mut Encoder<'a>|) {
+            self.emit_enum_variant("Some", 1, 1, f)
+        }
+
+        fn emit_seq(&mut self, len: uint, f: |&mut Encoder<'a>|) {
+            self.start_tag(EsVec as uint);
+            self._emit_tagged_uint(EsVecLen, len);
+            f(self);
+            self.end_tag();
+        }
+
+        fn emit_seq_elt(&mut self, _idx: uint, f: |&mut Encoder<'a>|) {
+            self.start_tag(EsVecElt as uint);
+            f(self);
+            self.end_tag();
+        }
+
+        fn emit_map(&mut self, len: uint, f: |&mut Encoder<'a>|) {
+            self.start_tag(EsMap as uint);
+            self._emit_tagged_uint(EsMapLen, len);
+            f(self);
+            self.end_tag();
+        }
+
+        fn emit_map_elt_key(&mut self, _idx: uint, f: |&mut Encoder<'a>|) {
+            self.start_tag(EsMapKey as uint);
+            f(self);
+            self.end_tag();
+        }
+
+        fn emit_map_elt_val(&mut self, _idx: uint, f: |&mut Encoder<'a>|) {
+            self.start_tag(EsMapVal as uint);
+            f(self);
+            self.end_tag();
+        }
+    }
+}
+
+// ___________________________________________________________________________
+// Testing
+
+#[cfg(test)]
+mod tests {
+    use ebml::reader;
+    use ebml::writer;
+    use {Encodable, Decodable};
+
+    use std::io::MemWriter;
+    use std::option::{None, Option, Some};
+
+    #[test]
+    fn test_vuint_at() {
+        let data = [
+            0x80,
+            0xff,
+            0x40, 0x00,
+            0x7f, 0xff,
+            0x20, 0x00, 0x00,
+            0x3f, 0xff, 0xff,
+            0x10, 0x00, 0x00, 0x00,
+            0x1f, 0xff, 0xff, 0xff
+        ];
+
+        let mut res: reader::Res;
+
+        // Class A
+        res = reader::vuint_at(data, 0);
+        assert_eq!(res.val, 0);
+        assert_eq!(res.next, 1);
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, (1 << 7) - 1);
+        assert_eq!(res.next, 2);
+
+        // Class B
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, 0);
+        assert_eq!(res.next, 4);
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, (1 << 14) - 1);
+        assert_eq!(res.next, 6);
+
+        // Class C
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, 0);
+        assert_eq!(res.next, 9);
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, (1 << 21) - 1);
+        assert_eq!(res.next, 12);
+
+        // Class D
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, 0);
+        assert_eq!(res.next, 16);
+        res = reader::vuint_at(data, res.next);
+        assert_eq!(res.val, (1 << 28) - 1);
+        assert_eq!(res.next, 20);
+    }
+
+    #[test]
+    fn test_option_int() {
+        fn test_v(v: Option<int>) {
+            debug!("v == {:?}", v);
+            let mut wr = MemWriter::new();
+            {
+                let mut ebml_w = writer::Encoder(&mut wr);
+                v.encode(&mut ebml_w);
+            }
+            let ebml_doc = reader::Doc(wr.get_ref());
+            let mut deser = reader::Decoder(ebml_doc);
+            let v1 = Decodable::decode(&mut deser);
+            debug!("v1 == {:?}", v1);
+            assert_eq!(v, v1);
+        }
+
+        test_v(Some(22));
+        test_v(None);
+        test_v(Some(3));
+    }
+}
+
+#[cfg(test)]
+mod bench {
+    use ebml::reader;
+    use extra::test::BenchHarness;
+
+    #[bench]
+    pub fn vuint_at_A_aligned(bh: &mut BenchHarness) {
+        use std::vec;
+        let data = vec::from_fn(4*100, |i| {
+            match i % 2 {
+              0 => 0x80u8,
+              _ => i as u8,
+            }
+        });
+        let mut sum = 0u;
+        bh.iter(|| {
+            let mut i = 0;
+            while i < data.len() {
+                sum += reader::vuint_at(data, i).val;
+                i += 4;
+            }
+        });
+    }
+
+    #[bench]
+    pub fn vuint_at_A_unaligned(bh: &mut BenchHarness) {
+        use std::vec;
+        let data = vec::from_fn(4*100+1, |i| {
+            match i % 2 {
+              1 => 0x80u8,
+              _ => i as u8
+            }
+        });
+        let mut sum = 0u;
+        bh.iter(|| {
+            let mut i = 1;
+            while i < data.len() {
+                sum += reader::vuint_at(data, i).val;
+                i += 4;
+            }
+        });
+    }
+
+    #[bench]
+    pub fn vuint_at_D_aligned(bh: &mut BenchHarness) {
+        use std::vec;
+        let data = vec::from_fn(4*100, |i| {
+            match i % 4 {
+              0 => 0x10u8,
+              3 => i as u8,
+              _ => 0u8
+            }
+        });
+        let mut sum = 0u;
+        bh.iter(|| {
+            let mut i = 0;
+            while i < data.len() {
+                sum += reader::vuint_at(data, i).val;
+                i += 4;
+            }
+        });
+    }
+
+    #[bench]
+    pub fn vuint_at_D_unaligned(bh: &mut BenchHarness) {
+        use std::vec;
+        let data = vec::from_fn(4*100+1, |i| {
+            match i % 4 {
+              1 => 0x10u8,
+              0 => i as u8,
+              _ => 0u8
+            }
+        });
+        let mut sum = 0u;
+        bh.iter(|| {
+            let mut i = 1;
+            while i < data.len() {
+                sum += reader::vuint_at(data, i).val;
+                i += 4;
+            }
+        });
+    }
+}