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Merge branch 'master' of github.com:gavofyork/ethcore-util

This commit is contained in:
Gav Wood 2015-11-29 20:11:12 +01:00
parent 06bbefd07b d23b8d9a74
commit f1315cff71
4 changed files with 259 additions and 137 deletions
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34
src/bytes.rs
View File

@ -23,7 +23,7 @@
//! use util::bytes::FromBytes;
//!
//! let a = String::from_bytes(&[b'd', b'o', b'g']);
//! let b = u8::from_bytes(&[0xfa]);
//! let b = u16::from_bytes(&[0xfa]);
//! let c = u64::from_bytes(&[0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]);
//! }
//!
@ -104,28 +104,6 @@ impl ToBytes for String {
fn to_bytes_len(&self) -> usize { self.len() }
}
impl ToBytes for u8 {
fn to_bytes(&self) -> Vec<u8> {
match *self {
0 => vec![],
_ => vec![*self]
}
}
fn to_bytes_len(&self) -> usize {
match *self {
0 => 0,
_ => 1
}
}
fn first_byte(&self) -> Option<u8> {
match *self {
0 => None,
_ => Some(*self)
}
}
}
impl ToBytes for u64 {
fn to_bytes(&self) -> Vec<u8> {
let mut res= vec![];
@ -223,15 +201,6 @@ impl FromBytes for String {
}
}
impl FromBytes for u8 {
fn from_bytes(bytes: &[u8]) -> FromBytesResult<u8> {
match bytes.len() {
0 => Ok(0),
_ => Ok(bytes[0])
}
}
}
impl FromBytes for u64 {
fn from_bytes(bytes: &[u8]) -> FromBytesResult<u64> {
match bytes.len() {
@ -293,3 +262,4 @@ impl <T>FromBytes for T where T: FixedHash {
}
}
}

165
src/rlp.rs
View File

@ -61,11 +61,11 @@
//! // [ [], [[]], [ [], [[]] ] ]
//! let data = vec![0xc7, 0xc0, 0xc1, 0xc0, 0xc3, 0xc0, 0xc1, 0xc0];
//! let rlp = Rlp::new(&data);
//! let _v0: Vec<u8> = Decodable::decode(&rlp.at(0));
//! let _v1: Vec<Vec<u8>> = Decodable::decode(&rlp.at(1));
//! let _v0: Vec<u16> = Decodable::decode(&rlp.at(0));
//! let _v1: Vec<Vec<u16>> = Decodable::decode(&rlp.at(1));
//! let nested_rlp = rlp.at(2);
//! let _v2a: Vec<u8> = Decodable::decode(&nested_rlp.at(0));
//! let _v2b: Vec<Vec<u8>> = Decodable::decode(&nested_rlp.at(1));
//! let _v2a: Vec<u16> = Decodable::decode(&nested_rlp.at(0));
//! let _v2b: Vec<Vec<u16>> = Decodable::decode(&nested_rlp.at(1));
//! }
//!
//! fn main() {
@ -343,9 +343,7 @@ pub fn decode<T>(bytes: &[u8]) -> T where T: Decodable {
}
/// shortcut function to decode UntrustedRlp `&[u8]` into an object
pub fn decode_untrusted<T>(bytes: &[u8]) -> Result<T, DecoderError>
where T: Decodable
{
pub fn decode_untrusted<T>(bytes: &[u8]) -> Result<T, DecoderError> where T: Decodable {
let rlp = UntrustedRlp::new(bytes);
T::decode_untrusted(&rlp)
}
@ -357,18 +355,18 @@ pub trait Decodable: Sized {
}
}
impl<T> Decodable for T where T: FromBytes
{
impl<T> Decodable for T where T: FromBytes {
fn decode_untrusted(rlp: &UntrustedRlp) -> Result<Self, DecoderError> {
match rlp.is_value() {
true => BasicDecoder::read_value(rlp.bytes),
true => BasicDecoder::read_value(rlp.bytes, | bytes | {
Ok(try!(T::from_bytes(bytes)))
}),
false => Err(DecoderError::UntrustedRlpExpectedToBeValue),
}
}
}
impl<T> Decodable for Vec<T> where T: Decodable
{
impl<T> Decodable for Vec<T> where T: Decodable {
fn decode_untrusted(rlp: &UntrustedRlp) -> Result<Self, DecoderError> {
match rlp.is_list() {
true => rlp.iter().map(|rlp| T::decode_untrusted(&rlp)).collect(),
@ -377,29 +375,40 @@ impl<T> Decodable for Vec<T> where T: Decodable
}
}
impl Decodable for Vec<u8> {
fn decode_untrusted(rlp: &UntrustedRlp) -> Result<Self, DecoderError> {
match rlp.is_value() {
true => BasicDecoder::read_value(rlp.bytes, | bytes | {
let mut res = vec![];
res.extend(bytes);
Ok(res)
}),
false => Err(DecoderError::UntrustedRlpExpectedToBeValue),
}
}
}
pub trait Decoder {
fn read_value<T>(bytes: &[u8]) -> Result<T, DecoderError> where T: FromBytes;
fn read_value<T, F>(bytes: &[u8], f: F) -> Result<T, DecoderError> where F: FnOnce(&[u8]) -> Result<T, DecoderError>;
}
struct BasicDecoder;
impl Decoder for BasicDecoder {
fn read_value<T>(bytes: &[u8]) -> Result<T, DecoderError>
where T: FromBytes
{
fn read_value<T, F>(bytes: &[u8], f: F) -> Result<T, DecoderError> where F: FnOnce(&[u8]) -> Result<T, DecoderError> {
match bytes.first().map(|&x| x) {
// rlp is too short
None => Err(DecoderError::UntrustedRlpIsTooShort),
// single byt value
Some(l @ 0...0x7f) => Ok(try!(T::from_bytes(&[l]))),
Some(l @ 0...0x7f) => Ok(try!(f(&[l]))),
// 0-55 bytes
Some(l @ 0x80...0xb7) => Ok(try!(T::from_bytes(&bytes[1..(1 + l as usize - 0x80)]))),
Some(l @ 0x80...0xb7) => Ok(try!(f(&bytes[1..(1 + l as usize - 0x80)]))),
// longer than 55 bytes
Some(l @ 0xb8...0xbf) => {
let len_of_len = l as usize - 0xb7;
let begin_of_value = 1 as usize + len_of_len;
let len = try!(usize::from_bytes(&bytes[1..begin_of_value]));
Ok(try!(T::from_bytes(&bytes[begin_of_value..begin_of_value + len])))
Ok(try!(f(&bytes[begin_of_value..begin_of_value + len])))
}
_ => Err(DecoderError::BadUntrustedRlp),
}
@ -478,7 +487,7 @@ impl RlpStream {
}
/// Appends raw (pre-serialised) RLP data. Use with caution. Chainable.
pub fn append_raw<'a>(&'a mut self, bytes: &[u8], item_count: usize) -> &'a RlpStream {
pub fn append_raw<'a>(&'a mut self, bytes: &[u8], item_count: usize) -> &'a mut RlpStream {
// push raw items
self.encoder.bytes.extend(bytes);
@ -525,8 +534,7 @@ impl RlpStream {
}
/// shortcut function to encode a `T: Encodable` into a UntrustedRlp `Vec<u8>`
pub fn encode<E>(object: &E) -> Vec<u8>
where E: Encodable
pub fn encode<E>(object: &E) -> Vec<u8> where E: Encodable
{
let mut encoder = BasicEncoder::new();
object.encode(&mut encoder);
@ -559,20 +567,14 @@ pub trait Encoder {
fn emit_list<F>(&mut self, f: F) -> () where F: FnOnce(&mut Self) -> ();
}
impl<T> Encodable for T where T: ToBytes
{
fn encode<E>(&self, encoder: &mut E) -> ()
where E: Encoder
{
impl<T> Encodable for T where T: ToBytes {
fn encode<E>(&self, encoder: &mut E) -> () where E: Encoder {
encoder.emit_value(&self.to_bytes())
}
}
impl<'a, T> Encodable for &'a [T] where T: Encodable + 'a
{
fn encode<E>(&self, encoder: &mut E) -> ()
where E: Encoder
{
impl<'a, T> Encodable for &'a [T] where T: Encodable + 'a {
fn encode<E>(&self, encoder: &mut E) -> () where E: Encoder {
encoder.emit_list(|e| {
// insert all list elements
for el in self.iter() {
@ -582,16 +584,29 @@ impl<'a, T> Encodable for &'a [T] where T: Encodable + 'a
}
}
impl<T> Encodable for Vec<T> where T: Encodable
{
fn encode<E>(&self, encoder: &mut E) -> ()
where E: Encoder
{
impl<T> Encodable for Vec<T> where T: Encodable {
fn encode<E>(&self, encoder: &mut E) -> () where E: Encoder {
let r: &[T] = self.as_ref();
r.encode(encoder)
}
}
/// lets treat bytes differently than other lists
/// they are a single value
impl<'a> Encodable for &'a [u8] {
fn encode<E>(&self, encoder: &mut E) -> () where E: Encoder {
encoder.emit_value(self)
}
}
/// lets treat bytes differently than other lists
/// they are a single value
impl Encodable for Vec<u8> {
fn encode<E>(&self, encoder: &mut E) -> () where E: Encoder {
encoder.emit_value(self)
}
}
struct BasicEncoder {
bytes: Vec<u8>,
}
@ -744,21 +759,7 @@ mod tests {
assert_eq!(res, &t.1[..]);
}
}
#[test]
fn encode_u8() {
let tests = vec![
ETestPair(0u8, vec![0x80u8]),
ETestPair(15, vec![15]),
ETestPair(55, vec![55]),
ETestPair(56, vec![56]),
ETestPair(0x7f, vec![0x7f]),
ETestPair(0x80, vec![0x81, 0x80]),
ETestPair(0xff, vec![0x81, 0xff]),
];
run_encode_tests(tests);
}
#[test]
fn encode_u16() {
let tests = vec![
@ -835,13 +836,15 @@ mod tests {
run_encode_tests(tests);
}
/// Vec<u8> is treated as a single value
#[test]
fn encode_vector_u8() {
let tests = vec![
ETestPair(vec![], vec![0xc0]),
ETestPair(vec![15u8], vec![0xc1, 0x0f]),
ETestPair(vec![1, 2, 3, 7, 0xff], vec![0xc6, 1, 2, 3, 7, 0x81, 0xff]),
];
ETestPair(vec![], vec![0x80]),
ETestPair(vec![0u8], vec![0]),
ETestPair(vec![0x15], vec![0x15]),
ETestPair(vec![0x40, 0x00], vec![0x82, 0x40, 0x00]),
];
run_encode_tests(tests);
}
@ -890,27 +893,23 @@ mod tests {
struct DTestPair<T>(T, Vec<u8>) where T: rlp::Decodable + fmt::Debug + cmp::Eq;
fn run_decode_untrusted_tests<T>(tests: Vec<DTestPair<T>>)
where T: rlp::Decodable + fmt::Debug + cmp::Eq
{
fn run_decode_tests<T>(tests: Vec<DTestPair<T>>) where T: rlp::Decodable + fmt::Debug + cmp::Eq {
for t in &tests {
let res: T = rlp::decode_untrusted(&t.1).unwrap();
assert_eq!(res, t.0);
}
}
/// Vec<u8> is treated as a single value
#[test]
fn decode_untrusted_u8() {
fn decode_vector_u8() {
let tests = vec![
DTestPair(0u8, vec![0u8]),
DTestPair(15, vec![15]),
DTestPair(55, vec![55]),
DTestPair(56, vec![56]),
DTestPair(0x7f, vec![0x7f]),
DTestPair(0x80, vec![0x81, 0x80]),
DTestPair(0xff, vec![0x81, 0xff]),
];
run_decode_untrusted_tests(tests);
DTestPair(vec![], vec![0x80]),
DTestPair(vec![0u8], vec![0]),
DTestPair(vec![0x15], vec![0x15]),
DTestPair(vec![0x40, 0x00], vec![0x82, 0x40, 0x00]),
];
run_decode_tests(tests);
}
#[test]
@ -920,7 +919,7 @@ mod tests {
DTestPair(0x100, vec![0x82, 0x01, 0x00]),
DTestPair(0xffff, vec![0x82, 0xff, 0xff]),
];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
@ -930,7 +929,7 @@ mod tests {
DTestPair(0x10000, vec![0x83, 0x01, 0x00, 0x00]),
DTestPair(0xffffff, vec![0x83, 0xff, 0xff, 0xff]),
];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
@ -940,7 +939,7 @@ mod tests {
DTestPair(0x1000000, vec![0x84, 0x01, 0x00, 0x00, 0x00]),
DTestPair(0xFFFFFFFF, vec![0x84, 0xff, 0xff, 0xff, 0xff]),
];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
@ -956,7 +955,7 @@ mod tests {
0x09, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x77, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x12, 0xf0])];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
@ -975,7 +974,7 @@ mod tests {
b't', b'e', b't', b'u', b'r', b' ', b'a', b'd', b'i',
b'p', b'i', b's', b'i', b'c', b'i', b'n', b'g', b' ',
b'e', b'l', b'i', b't'])];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
@ -988,17 +987,7 @@ mod tests {
0x36, 0xe0, 0xda, 0xbf, 0xce, 0x45, 0xd0, 0x46,
0xb3, 0x7d, 0x11, 0x06])
];
run_decode_untrusted_tests(tests);
}
#[test]
fn decode_untrusted_vector_u8() {
let tests = vec![
DTestPair(vec![] as Vec<u8>, vec![0xc0]),
DTestPair(vec![15u8], vec![0xc1, 0x0f]),
DTestPair(vec![1u8, 2, 3, 7, 0xff], vec![0xc6, 1, 2, 3, 7, 0x81, 0xff]),
];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
@ -1009,20 +998,20 @@ mod tests {
DTestPair(vec![1, 2, 3, 7, 0xff], vec![0xc6, 1, 2, 3, 7, 0x81, 0xff]),
DTestPair(vec![0xffffffff, 1, 2, 3, 7, 0xff], vec![0xcb, 0x84, 0xff, 0xff, 0xff, 0xff, 1, 2, 3, 7, 0x81, 0xff]),
];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
fn decode_untrusted_vector_str() {
let tests = vec![DTestPair(vec!["cat".to_string(), "dog".to_string()],
vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g'])];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
#[test]
fn decode_untrusted_vector_of_vectors_str() {
let tests = vec![DTestPair(vec![vec!["cat".to_string()]],
vec![0xc5, 0xc4, 0x83, b'c', b'a', b't'])];
run_decode_untrusted_tests(tests);
run_decode_tests(tests);
}
}

160
src/triehash.rs
View File

@ -6,6 +6,7 @@ use hash::*;
use sha3::*;
use rlp;
use rlp::RlpStream;
use vector::SharedPrefix;
/// Hex-prefix Notation. First nibble has flags: oddness = 2^0 & termination = 2^1.
///
@ -56,6 +57,11 @@ use rlp::RlpStream;
/// let e = vec![0x00, 0x12, 0x34];
/// let h = hex_prefix_encode(&v, false);
/// assert_eq!(h, e);
///
/// let v = vec![4, 1];
/// let e = vec![0x20, 0x41];
/// let h = hex_prefix_encode(&v, true);
/// assert_eq!(h, e);
/// }
/// ```
///
@ -97,6 +103,11 @@ pub fn hex_prefix_encode(nibbles: &[u8], leaf: bool) -> Vec<u8> {
/// let v = vec![0x31, 0x23, 0x45];
/// let e = vec![3, 1, 2, 3, 4, 5];
/// assert_eq!(as_nibbles(&v), e);
///
/// // A => 65 => 0x41 => [4, 1]
/// let v: Vec<u8> = From::from("A");
/// let e = vec![4, 1];
/// assert_eq!(as_nibbles(&v), e);
/// }
/// ```
pub fn as_nibbles(bytes: &[u8]) -> Vec<u8> {
@ -109,11 +120,25 @@ pub fn as_nibbles(bytes: &[u8]) -> Vec<u8> {
res
}
struct NibblePair {
#[derive(Debug)]
pub struct NibblePair {
nibble: Vec<u8>,
data: Vec<u8>
}
impl NibblePair {
pub fn new(nibble: Vec<u8>, data: Vec<u8>) -> NibblePair {
NibblePair {
nibble: nibble,
data: data
}
}
pub fn new_raw(to_nibble: Vec<u8>, data: Vec<u8>) -> NibblePair {
NibblePair::new(as_nibbles(&to_nibble), data)
}
}
pub fn ordered_trie_root(data: Vec<Vec<u8>>) -> H256 {
let vec: Vec<NibblePair> = data
// first put elements into btree to sort them by nibbles
@ -126,9 +151,13 @@ pub fn ordered_trie_root(data: Vec<Vec<u8>>) -> H256 {
})
// then move them to a vector
.into_iter()
.map(|(k, v)| NibblePair { nibble: k, data: v } )
.map(|(k, v)| NibblePair::new(k, v) )
.collect();
hash256(&vec)
}
pub fn hash256(vec: &[NibblePair]) -> H256 {
let out = match vec.len() {
0 => rlp::encode(&""),
_ => {
@ -138,34 +167,133 @@ pub fn ordered_trie_root(data: Vec<Vec<u8>>) -> H256 {
}
};
println!("out: {:?}", out);
out.sha3()
}
fn shared_prefix_length<T>(v1: &[T], v2: &[T]) -> usize where T: Eq {
let len = cmp::min(v1.len(), v2.len());
(0..len).take_while(|&i| v1[i] == v2[i]).count()
}
fn hash256rlp(vec: &[NibblePair], pre_len: usize, stream: &mut RlpStream) {
match vec.len() {
0 => stream.append(&""),
1 => stream.append_list(2).append(&hex_prefix_encode(&vec[0].nibble, true)).append(&vec[0].data),
0 => {
stream.append(&"");
},
1 => {
stream.append_list(2);
stream.append(&hex_prefix_encode(&vec[0].nibble[pre_len..], true));
stream.append(&vec[0].data);
},
_ => {
let shared_prefix = vec.iter()
// skip first element
.skip(1)
// get minimum number of shared nibbles between first string and each successive
.fold(usize::max_value(), | acc, pair | cmp::min(shared_prefix_length(&vec[0].nibble, &pair.nibble), acc) );
//match shared_prefix > pre_len {
// get minimum number of shared nibbles between first and each successive
.fold(usize::max_value(), | acc, pair | {
cmp::min(vec[0].nibble.shared_prefix_len(&pair.nibble), acc)
});
//true => hex_prefix_encode(&vec[0].nibble
//}
panic!();
match shared_prefix > pre_len {
true => {
stream.append_list(2);
stream.append(&hex_prefix_encode(&vec[0].nibble[pre_len..shared_prefix], false));
hash256aux(vec, shared_prefix, stream);
},
false => {
stream.append_list(17);
// every nibble is longer then previous one
let iter = vec.iter()
// move to first element with len different then pre_len
.take_while(| pair | { pair.nibble.len() == pre_len });
let mut begin = iter.count();
for i in 0..16 {
// cout how many successive elements have same next nibble
let len = vec[begin..].iter()
.map(| pair | pair.nibble[pre_len] )
.take_while(|&q| q == i).count();
match len {
0 => { stream.append(&""); },
_ => hash256aux(&vec[begin..begin + len], pre_len + 1, stream)
}
begin += len;
}
match pre_len == vec[0].nibble.len() {
true => stream.append(&vec[0].data),
false => stream.append(&"")
};
}
}
}
};
}
fn hash256aux(vec: &[NibblePair], pre_len: usize, stream: &mut RlpStream) {
let mut s = RlpStream::new();
hash256rlp(vec, pre_len, &mut s);
let out = s.out().unwrap();
match out.len() {
0...31 => stream.append_raw(&out, 1),
_ => stream.append(&out.sha3())
};
}
#[cfg(test)]
mod tests {
use std::str::FromStr;
use rustc_serialize::hex::FromHex;
use hash::*;
use triehash::*;
#[test]
fn empty_trie_root() {
assert_eq!(hash256(&vec![]), H256::from_str("56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421").unwrap());
}
#[test]
fn single_trie_item() {
let v = vec![
NibblePair::new_raw(From::from("A"),
From::from("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"))
];
assert_eq!(hash256(&v), H256::from_str("d23786fb4a010da3ce639d66d5e904a11dbc02746d1ce25029e53290cabf28ab").unwrap());
}
#[test]
fn test_trie_root() {
let _v = vec![
NibblePair::new_raw("0000000000000000000000000000000000000000000000000000000000000045".from_hex().unwrap(),
"22b224a1420a802ab51d326e29fa98e34c4f24ea".from_hex().unwrap()),
NibblePair::new_raw("0000000000000000000000000000000000000000000000000000000000000046".from_hex().unwrap(),
"67706c2076330000000000000000000000000000000000000000000000000000".from_hex().unwrap()),
NibblePair::new_raw("000000000000000000000000697c7b8c961b56f675d570498424ac8de1a918f6".from_hex().unwrap(),
"6f6f6f6820736f2067726561742c207265616c6c6c793f000000000000000000".from_hex().unwrap()),
NibblePair::new_raw("0000000000000000000000007ef9e639e2733cb34e4dfc576d4b23f72db776b2".from_hex().unwrap(),
"4655474156000000000000000000000000000000000000000000000000000000".from_hex().unwrap()),
NibblePair::new_raw("000000000000000000000000ec4f34c97e43fbb2816cfd95e388353c7181dab1".from_hex().unwrap(),
"4e616d6552656700000000000000000000000000000000000000000000000000".from_hex().unwrap()),
NibblePair::new_raw("4655474156000000000000000000000000000000000000000000000000000000".from_hex().unwrap(),
"7ef9e639e2733cb34e4dfc576d4b23f72db776b2".from_hex().unwrap()),
NibblePair::new_raw("4e616d6552656700000000000000000000000000000000000000000000000000".from_hex().unwrap(),
"ec4f34c97e43fbb2816cfd95e388353c7181dab1".from_hex().unwrap()),
NibblePair::new_raw("6f6f6f6820736f2067726561742c207265616c6c6c793f000000000000000000".from_hex().unwrap(),
"697c7b8c961b56f675d570498424ac8de1a918f6".from_hex().unwrap())
];
let _root = H256::from_str("9f6221ebb8efe7cff60a716ecb886e67dd042014be444669f0159d8e68b42100").unwrap();
//let res = hash256(&v);
//println!("{:?}", res);
//assert_eq!(res, root);
}
}

37
src/vector.rs
View File

@ -1,3 +1,5 @@
//! vector util functions
use std::ptr;
pub trait InsertSlice<T> {
@ -32,5 +34,38 @@ impl<T> InsertSlice<T> for Vec<T> {
}
}
pub trait SharedPreifx {
/// Returns len of prefix shared with elem
///
/// ```rust
/// extern crate ethcore_util as util;
/// use util::vector::SharedPrefix;
///
/// fn main () {
/// let a = vec![1,2,3,3,5];
/// let b = vec![1,2,3];
/// assert_eq!(a.shared_prefix_len(&b), 3);
/// }
/// ```
pub trait SharedPrefix <T> {
fn shared_prefix_len(&self, elem: &[T]) -> usize;
}
impl <T> SharedPrefix<T> for Vec<T> where T: Eq {
fn shared_prefix_len(&self, elem: &[T]) -> usize {
use std::cmp;
let len = cmp::min(self.len(), elem.len());
(0..len).take_while(|&i| self[i] == elem[i]).count()
}
}
#[cfg(test)]
mod test {
use vector::SharedPrefix;
#[test]
fn test_shared_prefix() {
let a = vec![1,2,3,3,5];
let b = vec![1,2,3];
assert_eq!(a.shared_prefix_len(&b), 3);
}
}