rust/src/lib/rope.rs

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2011-11-04 12:38:42 -05:00
/*
Module: rope
High-level text containers.
Ropes are a high-level representation of text that offers
much better performance than strings for common operations,
and generally reduce memory allocations and copies, while only
entailing a small degradation of less common operations.
More precisely, where a string is represented as a memory buffer,
a rope is a tree structure whose leaves are slices of immutable
strings. Therefore, concatenation, appending, prepending, substrings,
etc. are operations that require only trivial tree manipulation,
generally without having to copy memory. In addition, the tree
structure of ropes makes them suitable as a form of index to speed-up
access to Unicode characters by index in long chunks of text.
The following operations are algorithmically faster in ropes:
- extracting a subrope is logarithmic (linear in strings);
- appending/prepending is near-constant time (linear in strings);
- concatenation is near-constant time (linear in strings);
- char length is constant-time (linear in strings);
- access to a character by index is logarithmic (linear in strings);
*/
/*
Type: rope
The type of ropes.
*/
type rope = node::root;
/*
Section: Creating a rope
*/
/*
Function:empty
Create an empty rope
*/
fn empty() -> rope {
ret node::empty;
}
/*
Function: of_str
Adopt a string as a rope.
Parameters:
str - A valid string.
Returns:
A rope representing the same string as `str`. Depending of the length
of `str`, this rope may be empty, flat or complex.
Performance notes:
- this operation does not copy the string;
- the function runs in linear time.
*/
fn of_str(str: @str) -> rope {
ret of_substr(str, 0u, str::byte_len(*str));
}
/*
Function: of_substr
As `of_str` but for a substring.
Performance note:
- this operation does not copy the substring.
Parameters:
byte_offset - The offset of `str` at which the rope starts.
byte_len - The number of bytes of `str` to use.
Returns:
A rope representing the same string as
`str::substr(str, byte_offset, byte_len)`.
Depending on `byte_len`, this rope may be empty, flat or complex.
Safety notes:
- this function does _not_ check the validity of the substring;
- this function fails if `byte_offset` or `byte_len` do not match `str`.
*/
fn of_substr(str: @str, byte_offset: uint, byte_len: uint) -> rope {
if byte_len == 0u { ret node::empty; }
ret node::content(node::of_substr(str, byte_offset, byte_len));
}
/*
Section: Adding things to a rope
*/
/*
Function: append_char
Add one char to the end of the rope
Performance note:
- this function executes in near-constant time
*/
fn append_char(rope: rope, char: char) -> rope {
ret append_str(rope, @str::from_chars([char]));
}
/*
Function: append_str
Add one string to the end of the rope
Performance note:
- this function executes in near-linear time
*/
fn append_str(rope: rope, str: @str) -> rope {
ret append_rope(rope, of_str(str))
}
/*
Function: prepend_char
Add one char to the beginning of the rope
Performance note:
- this function executes in near-constant time
*/
fn prepend_char(rope: rope, char: char) -> rope {
ret prepend_str(rope, @str::from_chars([char]));
}
/*
Function: prepend_str
Add one string to the beginning of the rope
Performance note:
- this function executes in near-linear time
*/
fn prepend_str(rope: rope, str: @str) -> rope {
ret append_rope(of_str(str), rope)
}
/*
Function: append_rope
Concatenate two ropes
*/
fn append_rope(left: rope, right: rope) -> rope {
alt(left) {
node::empty. { ret right; }
node::content(left_content) {
alt(right) {
node::empty. { ret left; }
node::content(right_content) {
ret node::content(node::concat2(left_content, right_content));
}
}
}
}
}
/*
Function: concat
Concatenate many ropes
*/
fn concat(v: [rope]) -> rope {
let acc = node::empty;
for r: rope in v {
acc = append_rope(acc, r);
}
ret bal(acc);
}
/*
Section: Keeping ropes healthy
*/
/*
Function: bal
Balance a rope.
Returns:
A copy of the rope in which small nodes have been grouped in memory,
and with a reduced height.
If you perform numerous rope concatenations, it is generally a good idea
to rebalance your rope at some point, before using it for other purposes.
*/
fn bal(rope:rope) -> rope {
alt(rope) {
node::empty. { ret rope }
node::content(x) {
alt(node::bal(x)) {
option::none. { rope }
option::some(y) { node::content(y) }
}
}
}
}
/*
Section: Transforming ropes
*/
/*
Function: sub_chars
Extract a subrope from a rope.
Performance note:
- on a balanced rope, this operation takes algorithmic time;
- this operation does not involve any copying
Safety note:
- this function fails if char_offset/char_len do not represent
valid positions in rope
*/
fn sub_chars(rope: rope, char_offset: uint, char_len: uint) -> rope {
if char_len == 0u { ret node::empty; }
alt(rope) {
node::empty. { fail }
node::content(node) {
if char_len > node::char_len(node) { fail }
else {
ret node::content(node::sub_chars(node, char_offset, char_len))
}
}
}
}
/*
Function:sub_bytes
Extract a subrope from a rope.
Performance note:
- on a balanced rope, this operation takes algorithmic time;
- this operation does not involve any copying
Safety note:
- this function fails if byte_offset/byte_len do not represent
valid positions in rope
*/
fn sub_bytes(rope: rope, byte_offset: uint, byte_len: uint) -> rope {
if byte_len == 0u { ret node::empty; }
alt(rope) {
node::empty. { fail }
node::content(node) {
if byte_len > node::byte_len(node) { fail }
else {
ret node::content(node::sub_bytes(node, byte_offset, byte_len))
}
}
}
}
/*
Section: Comparing ropes
*/
/*
Function: cmp
Compare two ropes by Unicode lexicographical order.
This function compares only the contents of the rope, not their structure.
Returns:
A negative value if `left < right`, 0 if eq(left, right) or a positive
value if `left > right`
*/
fn cmp(left: rope, right: rope) -> int {
alt((left, right)) {
(node::empty., node::empty.) { ret 0; }
(node::empty., _) { ret -1;}
(_, node::empty.) { ret 1;}
(node::content(a), node::content(b)) {
ret node::cmp(a, b);
}
}
}
fn eq(left: rope, right: rope) -> bool {
ret cmp(left, right) == 0;
}
fn leq(left: rope, right: rope) -> bool {
ret cmp(left, right) <= 0;
}
fn lt(left: rope, right: rope) -> bool {
ret cmp(left, right) < 0;
}
fn geq(left: rope, right: rope) -> bool {
ret cmp(left, right) >= 0;
}
fn gt(left: rope, right: rope) -> bool {
ret cmp(left, right) > 0;
}
/*
Section: Iterating
*/
/*
Function: loop_chars
Loop through a rope, char by char
While other mechanisms are available, this is generally the best manner
of looping through the contents of a rope char by char. If you prefer a
loop that iterates through the contents string by string (e.g. to print
the contents of the rope or output it to the system), however,
you should rather use `traverse_components`.
Parameters:
rope - A rope to traverse. It may be empty.
it - A block to execute with each consecutive character of the rope.
Return `true` to continue, `false` to stop.
Returns:
`true` If execution proceeded correctly, `false` if it was interrupted,
that is if `it` returned `false` at any point.
*/
fn loop_chars(rope: rope, it: block(char) -> bool) -> bool {
alt(rope) {
node::empty. { ret true }
node::content(x) { ret node::loop_chars(x, it) }
}
}
fn iter_chars(rope: rope, it: block(char)) {
loop_chars(rope) {|x|
it(x);
ret true
}
}
/*
Function: loop_leaves
Loop through a rope, string by string
While other mechanisms are available, this is generally the best manner of
looping through the contents of a rope string by string, which may be useful
e.g. to print strings as you see them (without having to copy their
contents into a new string), to send them to then network, to write them to
a file, etc.. If you prefer a loop that iterates through the contents
char by char (e.g. to search for a char), however, you should rather
use `traverse`.
Parameters:
rope - A rope to traverse. It may be empty.
it - A block to execute with each consecutive string component of the rope.
Return `true` to continue, `false` to stop.
Returns:
`true` If execution proceeded correctly, `false` if it was interrupted,
that is if `it` returned `false` at any point.
*/
fn loop_leaves(rope: rope, it: block(node::leaf) -> bool) -> bool{
alt(rope) {
node::empty. { ret true }
node::content(x) {ret node::loop_leaves(x, it)}
}
}
mod iterator {
mod leaf {
fn start(rope: rope) -> node::leaf_iterator::t {
alt(rope) {
node::empty. { ret node::leaf_iterator::empty() }
node::content(x) { ret node::leaf_iterator::start(x) }
}
}
fn next(it: node::leaf_iterator::t) -> option::t<node::leaf> {
ret node::leaf_iterator::next(it);
}
}
mod char {
fn start(rope: rope) -> node::char_iterator::t {
alt(rope) {
node::empty. { ret node::char_iterator::empty() }
node::content(x) { ret node::char_iterator::start(x) }
}
}
fn next(it: node::char_iterator::t) -> option::t<char> {
ret node::char_iterator::next(it)
}
}
}
/*
Section: Rope properties
*/
/*
Function: height
Returns: The height of the rope, i.e. a bound on the number of
operations which must be performed during a character access before
finding the leaf in which a character is contained.
Performance note: Constant time.
*/
fn height(rope: rope) -> uint {
alt(rope) {
node::empty. { ret 0u; }
node::content(x) { ret node::height(x); }
}
}
/*
Function: char_len
Returns: The number of character in the rope
Performance note: Constant time.
*/
pure fn char_len(rope: rope) -> uint {
alt(rope) {
node::empty. { ret 0u; }
node::content(x) { ret node::char_len(x) }
}
}
/*
Function: char_len
Returns: The number of bytes in the rope
Performance note: Constant time.
*/
pure fn byte_len(rope: rope) -> uint {
alt(rope) {
node::empty. { ret 0u; }
node::content(x) { ret node::byte_len(x) }
}
}
/*
Function: char_at
Parameters:
pos - A position in the rope
Returns: The character at position `pos`
Safety notes: The function will fail if `pos`
is not a valid position in the rope.
Performance note: This function executes in a time
proportional to the height of the rope + the (bounded)
length of the largest leaf.
*/
fn char_at(rope: rope, pos: uint) -> char {
alt(rope) {
node::empty. { fail }
node::content(x) { ret node::char_at(x, pos) }
}
}
/*
Section: Implementation
*/
mod node {
/*
Enum: node::root
Implementation of type `rope`
Constants:
empty - An empty rope
content - A non-empty rope
*/
tag root {
empty;
content(@node);
}
/*
Struct: node::leaf
A text component in a rope.
This is actually a slice in a rope, so as to ensure maximal sharing.
*/
type leaf = {
/*
Field: byte_offset
The number of bytes skipped in `content`
*/
byte_offset: uint,
/*
Field: byte_len
The number of bytes of `content` to use
*/
byte_len: uint,
/*
Field: char_len
The number of chars in the leaf.
*/
char_len: uint,
/*
Field: content
Contents of the leaf.
Note that we can have `char_len < str::char_len(content)`, if this
leaf is only a subset of the string. Also note that the string
can be shared between several ropes, e.g. for indexing purposes.
*/
content: @str
};
/*
Struct node::concat
A node obtained from the concatenation of two other nodes
*/
type concat = {
/*
Field: left
The node containing the beginning of the text.
*/
left: @node,//TODO: Perhaps a `vec` instead of `left`/`right`
/*
Field: right
The node containing the end of the text.
*/
right: @node,
/*
Field: char_len
The number of chars contained in all leaves of this node.
*/
char_len: uint,
/*
Field: byte_len
The number of bytes in the subrope.
Used to pre-allocate the correct amount of storage for serialization.
*/
byte_len: uint,
/*
Field: height
Height of the subrope.
Used for rebalancing and to allocate stacks for
traversals.
*/
height: uint
};
/*
Enum: node::node
leaf - A leaf consisting in a `str`
concat - The concatenation of two ropes
*/
tag node {
leaf(leaf);
concat(concat);
}
/*
The maximal number of chars that _should_ be permitted in a single node.
This is not a strict value
*/
const hint_max_leaf_char_len: uint = 256u;
/*
The maximal height that _should_ be permitted in a tree.
This is not a strict value
*/
const hint_max_node_height: uint = 16u;
/*
Adopt a string as a node.
If the string is longer than `max_leaf_char_len`, it is
logically split between as many leaves as necessary. Regardless,
the string itself is not copied.
Performance note: The complexity of this function is linear in
the length of `str`.
*/
fn of_str(str: @str) -> @node {
ret of_substr(str, 0u, str::byte_len(*str));
}
/*
Adopt a slice of a string as a node.
If the slice is longer than `max_leaf_char_len`, it is logically split
between as many leaves as necessary. Regardless, the string itself
is not copied.
@param byte_start The byte offset where the slice of `str` starts.
@param byte_len The number of bytes from `str` to use.
*/
fn of_substr(str: @str, byte_start: uint, byte_len: uint) -> @node {
assert (byte_len > 0u);
let char_len = str::char_len_range(*str, byte_start, byte_len);
let candidate = @leaf({
byte_offset: byte_start,
byte_len: byte_len,
char_len: char_len,
content: str});
if char_len <= hint_max_leaf_char_len {
ret candidate;
} else {
//Firstly, split `str` in slices of hint_max_leaf_char_len
let leaves = uint::div_ceil(char_len, hint_max_leaf_char_len);
//Number of leaves
let nodes = vec::init_elt_mut(candidate, leaves);
let i = 0u;
let offset = byte_start;
let first_leaf_char_len =
if char_len%hint_max_leaf_char_len == 0u {
hint_max_leaf_char_len
} else {
char_len%hint_max_leaf_char_len
};
while i < leaves {
let chunk_char_len: uint =
if i == 0u { first_leaf_char_len }
else { hint_max_leaf_char_len };
let chunk_byte_len =
str::byte_len_range(*str, offset, chunk_char_len);
nodes[i] = @leaf({
byte_offset: offset,
byte_len: chunk_byte_len,
char_len: chunk_char_len,
content: str
});
offset += chunk_byte_len;
i += 1u;
}
//Then, build a tree from these slices by collapsing them
while leaves > 1u {
i = 0u;
while i < leaves - 1u {//Concat nodes 0 with 1, 2 with 3 etc.
nodes[i/2u] = concat2(nodes[i], nodes[i + 1u]);
i += 2u;
}
if i == leaves - 1u {
//And don't forget the last node if it is in even position
nodes[i/2u] = nodes[i];
}
leaves = uint::div_ceil(leaves, 2u);
}
ret nodes[0u];
}
}
pure fn byte_len(node: @node) -> uint {
alt(*node) {//TODO: Could we do this without the pattern-matching?
leaf(y) { ret y.byte_len; }
concat(y){ ret y.byte_len; }
}
}
pure fn char_len(node: @node) -> uint {
alt(*node) {
leaf(y) { ret y.char_len; }
concat(y) { ret y.char_len; }
}
}
fn tree_from_forest_destructive(forest: [mutable @node]) -> @node {
let i = 0u;
let len = vec::len(forest);
while len > 1u {
i = 0u;
while i < len - 1u {//Concat nodes 0 with 1, 2 with 3 etc.
let left = forest[i];
let right = forest[i+1u];
let left_len = char_len(left);
let right_len= char_len(right);
let left_height= height(left);
let right_height=height(right);
if left_len + right_len > hint_max_leaf_char_len
//TODO: Improve strategy
|| left_height >= hint_max_node_height
|| right_height >= hint_max_node_height {
if left_len <= hint_max_leaf_char_len {
left = flatten(left);
}
if right_len <= hint_max_leaf_char_len {
right = flatten(right);
}
}
forest[i/2u] = concat2(left, right);
i += 2u;
}
if i == len - 1u {
//And don't forget the last node if it is in even position
forest[i/2u] = forest[i];
}
len = uint::div_ceil(len, 2u);
}
ret forest[0];
}
fn serialize_node(node: @node) -> str unsafe {
let buf = vec::init_elt_mut(0u8, byte_len(node));
let offset = 0u;//Current position in the buffer
let it = leaf_iterator::start(node);
while true {
alt(leaf_iterator::next(it)) {
option::none. { break; }
option::some(x) {
//TODO: Replace with memcpy or something similar
let local_buf: [u8] = unsafe::reinterpret_cast(*x.content);
let i = x.byte_offset;
while i < x.byte_len {
buf[offset] = local_buf[i];
offset += 1u;
i += 1u;
}
unsafe::leak(local_buf);
}
}
}
let str : str = unsafe::reinterpret_cast(buf);
unsafe::leak(buf);//TODO: Check if this is correct
ret str;
}
/*
Replace a subtree by a single leaf with the same contents.
*/
fn flatten(node: @node) -> @node unsafe {
alt(*node) {
leaf(_) { ret node }
concat(x) {
ret @leaf({
byte_offset: 0u,
byte_len: x.byte_len,
char_len: x.char_len,
content: @serialize_node(node)
})
}
}
}
fn bal(node: @node) -> option::t<@node> {
if height(node) < hint_max_node_height { ret option::none }
else {
//1. Gather all leaves as a forest
let forest = [mutable];
let it = leaf_iterator::start(node);
while true {
alt (leaf_iterator::next(it)) {
option::none. { break; }
option::some(x) { forest += [mutable @leaf(x)]; }
}
}
//2. Rebuild tree from forest
let root = @*tree_from_forest_destructive(forest);
ret option::some(root);
}
}
fn sub_bytes(node: @node, byte_offset: uint, byte_len: uint) -> @node {
let node = node;
let result = node;//Arbitrary value
let byte_offset = byte_offset;
let byte_len = byte_len;
while true {
if byte_offset == 0u && byte_len == node::byte_len(node) {
result = node;
break;
}
alt(*node) {
node::leaf(x) {
let char_len =
str::char_len_range(*x.content, byte_offset, byte_len);
result = @leaf({byte_offset: byte_offset,
byte_len: byte_len,
char_len: char_len,
content: x.content});
break;
}
node::concat(x) {
let left_len: uint = node::byte_len(x.left);
if byte_offset <= left_len {
if byte_offset + byte_len <= left_len {
//Case 1: Everything fits in x.left, tail-call
node = x.left;
} else {
//Case 2: A (non-empty, possibly full) suffix
//of x.left and a (non-empty, possibly full) prefix
//of x.right
let left_result =
sub_bytes(x.left, byte_offset, left_len);
let right_result =
sub_bytes(x.right, 0u, left_len - byte_offset);
result = concat2(left_result, right_result);
break;
}
} else {
//Case 3: Everything fits in x.right
byte_offset -= left_len;
node = x.right;
}
}
}
}
ret result;
}
fn sub_chars(node: @node, char_offset: uint, char_len: uint) -> @node {
alt(*node) {
node::leaf(x) {
if char_offset == 0u && char_len == x.char_len {
ret node;
}
let byte_offset =
str::byte_len_range(*x.content, 0u, char_offset);
let byte_len =
str::byte_len_range(*x.content, byte_offset, char_len);
ret @leaf({byte_offset: byte_offset,
byte_len: byte_len,
char_len: char_len,
content: x.content});
}
node::concat(x) {
if char_offset == 0u && char_len == x.char_len {ret node;}
let left_len : uint = node::char_len(x.left);
if char_offset <= left_len {
if char_offset + char_len <= left_len {
//Case 1: Everything fits in x.left
ret sub_chars(x.left, char_offset, char_len);
//TODO: Optimize manually this tail call?
} else {
//Case 2: A (non-empty, possibly full) suffix
//of x.left and a (non-empty, possibly full) prefix
//of x.right
let left_result =
sub_chars(x.left, char_offset, left_len);
let right_result =
sub_chars(x.right, 0u, left_len - char_offset);
ret concat2(left_result, right_result)
}
} else {
//Case 3: Everything fits in x.right
ret sub_chars(x.right, char_offset - left_len, char_len);
//TODO: Optimize manually this tail call?
}
}
}
}
fn concat2(left: @node, right: @node) -> @node {
ret @concat({left : left,
right : right,
char_len: char_len(left) + char_len(right),
byte_len: byte_len(left) + byte_len(right),
height: math::max(height(left), height(right)) + 1u
})
}
fn height(node: @node) -> uint {
alt(*node) {
leaf(_) { ret 0u; }
concat(x) { ret x.height; }
}
}
fn cmp(a: @node, b: @node) -> int {
let ita = char_iterator::start(a);
let itb = char_iterator::start(b);
let result = 0;
let pos = 0u;
while result == 0 {
alt((char_iterator::next(ita), char_iterator::next(itb))) {
(option::none., option::none.) {
break;
}
(option::some(chara), option::some(charb)) {
result = char::cmp(chara, charb);
}
(option::some(_), _) {
result = 1;
}
(_, option::some(_)) {
result = -1;
}
}
pos += 1u;
}
ret result;
}
fn loop_chars(node: @node, it: block(char) -> bool) -> bool {
ret loop_leaves(node, {|leaf|
ret str::loop_chars_sub(*leaf.content,
leaf.byte_offset,
leaf.byte_len, it)
})
}
fn loop_leaves(node: @node, it: block(leaf) -> bool) -> bool{
let result = true;
let current = node;
while true {
alt(*current) {
leaf(x) {
result = it(x);
break;
}
concat(x) {
if loop_leaves(x.left, it) { //non tail call
current = x.right; //tail call
} else {
result = false;
break;
}
}
}
}
ret result;
}
fn char_at(node: @node, pos: uint) -> char {
let node = node;
let pos = pos;
let result = '0';
while true {
alt(*node) {
leaf(x) {
result = str::char_at(*x.content, pos);
break;
}
concat({left: left,
right: right,
char_len: _,
byte_len: _,
height: _}) {
let left_len = char_len(left);
if left_len > pos {
node = left;
} else {
node = right;
pos = pos - left_len;
}
}
}
};
ret result;
}
mod leaf_iterator {
type t = {
stack: [mutable @node],
mutable stackpos: int
};
fn empty() -> t {
let stack : [mutable @node] = [mutable];
ret {stack: stack, mutable stackpos: -1}
}
fn start(node: @node) -> t {
let stack = vec::init_elt_mut(node, height(node)+1u);
ret {
stack: stack,
mutable stackpos: 0
}
}
fn next(it: t) -> option::t<leaf> {
if it.stackpos < 0 { ret option::none; }
let result = option::none;
while true {
let current = it.stack[it.stackpos];
it.stackpos -= 1;
alt(*current) {
concat(x) {
it.stackpos += 1;
it.stack[it.stackpos] = x.right;
it.stackpos += 1;
it.stack[it.stackpos] = x.left;
}
leaf(x) {
result = option::some(x);
break;
}
}
}
ret result;
}
}
mod char_iterator {
type t = {
leaf_iterator: leaf_iterator::t,
mutable leaf: option::t<leaf>,
mutable leaf_byte_pos: uint
};
fn start(node: @node) -> t {
ret {
leaf_iterator: leaf_iterator::start(node),
mutable leaf: option::none,
mutable leaf_byte_pos: 0u
}
}
fn empty() -> t {
ret {
leaf_iterator: leaf_iterator::empty(),
mutable leaf: option::none,
mutable leaf_byte_pos: 0u
}
}
fn next(it: t) -> option::t<char> {
let result = option::none;
while true {
alt(get_current_or_next_leaf(it)) {
option::none. {
break;
}
option::some(leaf) {
let next_char = get_next_char_in_leaf(it);
alt(next_char) {
option::none. {
cont;
}
option::some(_) {
result = next_char;
break;
}
}
}
}
}
ret result;
}
fn get_current_or_next_leaf(it: t) -> option::t<leaf> {
alt(it.leaf) {
option::some(_) { ret it.leaf }
option::none. {
let next = leaf_iterator::next(it.leaf_iterator);
alt(next) {
option::none. { ret option::none }
option::some(leaf) {
it.leaf = next;
it.leaf_byte_pos = 0u;
ret next;
}
}
}
}
}
fn get_next_char_in_leaf(it: t) -> option::t<char> {
alt(it.leaf) {
option::none. { ret option::none }
option::some(leaf) {
if it.leaf_byte_pos >= leaf.byte_len {
//We are actually past the end of the leaf
it.leaf = option::none;
ret option::none
} else {
let {ch, next} =
str::char_range_at(*leaf.content,
it.leaf_byte_pos + leaf.byte_offset);
it.leaf_byte_pos = next - leaf.byte_offset;
ret option::some(ch)
}
}
}
}
}
}