nodemap.rs
160 lines
| 4.7 KiB
| application/rls-services+xml
|
RustLexer
Georges Racinet
|
r44600 | // Copyright 2018-2020 Georges Racinet <georges.racinet@octobus.net> | ||
// and Mercurial contributors | ||||
// | ||||
// This software may be used and distributed according to the terms of the | ||||
// GNU General Public License version 2 or any later version. | ||||
//! Indexing facilities for fast retrieval of `Revision` from `Node` | ||||
//! | ||||
//! This provides a variation on the 16-ary radix tree that is | ||||
//! provided as "nodetree" in revlog.c, ready for append-only persistence | ||||
//! on disk. | ||||
//! | ||||
//! Following existing implicit conventions, the "nodemap" terminology | ||||
//! is used in a more abstract context. | ||||
use super::Revision; | ||||
use std::fmt; | ||||
/// Low level NodeTree [`Blocks`] elements | ||||
/// | ||||
/// These are exactly as for instance on persistent storage. | ||||
type RawElement = i32; | ||||
/// High level representation of values in NodeTree | ||||
/// [`Blocks`](struct.Block.html) | ||||
/// | ||||
/// This is the high level representation that most algorithms should | ||||
/// use. | ||||
#[derive(Clone, Debug, Eq, PartialEq)] | ||||
enum Element { | ||||
Rev(Revision), | ||||
Block(usize), | ||||
None, | ||||
} | ||||
impl From<RawElement> for Element { | ||||
/// Conversion from low level representation, after endianness conversion. | ||||
/// | ||||
/// See [`Block`](struct.Block.html) for explanation about the encoding. | ||||
fn from(raw: RawElement) -> Element { | ||||
if raw >= 0 { | ||||
Element::Block(raw as usize) | ||||
} else if raw == -1 { | ||||
Element::None | ||||
} else { | ||||
Element::Rev(-raw - 2) | ||||
} | ||||
} | ||||
} | ||||
impl From<Element> for RawElement { | ||||
fn from(element: Element) -> RawElement { | ||||
match element { | ||||
Element::None => 0, | ||||
Element::Block(i) => i as RawElement, | ||||
Element::Rev(rev) => -rev - 2, | ||||
} | ||||
} | ||||
} | ||||
/// A logical block of the `NodeTree`, packed with a fixed size. | ||||
/// | ||||
/// These are always used in container types implementing `Index<Block>`, | ||||
/// such as `&Block` | ||||
/// | ||||
/// As an array of integers, its ith element encodes that the | ||||
/// ith potential edge from the block, representing the ith hexadecimal digit | ||||
/// (nybble) `i` is either: | ||||
/// | ||||
/// - absent (value -1) | ||||
/// - another `Block` in the same indexable container (value ≥ 0) | ||||
/// - a `Revision` leaf (value ≤ -2) | ||||
/// | ||||
/// Endianness has to be fixed for consistency on shared storage across | ||||
/// different architectures. | ||||
/// | ||||
/// A key difference with the C `nodetree` is that we need to be | ||||
/// able to represent the [`Block`] at index 0, hence -1 is the empty marker | ||||
/// rather than 0 and the `Revision` range upper limit of -2 instead of -1. | ||||
/// | ||||
/// Another related difference is that `NULL_REVISION` (-1) is not | ||||
/// represented at all, because we want an immutable empty nodetree | ||||
/// to be valid. | ||||
#[derive(Clone, PartialEq)] | ||||
pub struct Block([RawElement; 16]); | ||||
impl Block { | ||||
fn new() -> Self { | ||||
Block([-1; 16]) | ||||
} | ||||
fn get(&self, nybble: u8) -> Element { | ||||
Element::from(RawElement::from_be(self.0[nybble as usize])) | ||||
} | ||||
fn set(&mut self, nybble: u8, element: Element) { | ||||
self.0[nybble as usize] = RawElement::to_be(element.into()) | ||||
} | ||||
} | ||||
impl fmt::Debug for Block { | ||||
/// sparse representation for testing and debugging purposes | ||||
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||||
f.debug_map() | ||||
.entries((0..16).filter_map(|i| match self.get(i) { | ||||
Element::None => None, | ||||
element => Some((i, element)), | ||||
})) | ||||
.finish() | ||||
} | ||||
} | ||||
#[cfg(test)] | ||||
mod tests { | ||||
use super::*; | ||||
/// Creates a `Block` using a syntax close to the `Debug` output | ||||
macro_rules! block { | ||||
{$($nybble:tt : $variant:ident($val:tt)),*} => ( | ||||
{ | ||||
let mut block = Block::new(); | ||||
$(block.set($nybble, Element::$variant($val)));*; | ||||
block | ||||
} | ||||
) | ||||
} | ||||
#[test] | ||||
fn test_block_debug() { | ||||
let mut block = Block::new(); | ||||
block.set(1, Element::Rev(3)); | ||||
block.set(10, Element::Block(0)); | ||||
assert_eq!(format!("{:?}", block), "{1: Rev(3), 10: Block(0)}"); | ||||
} | ||||
#[test] | ||||
fn test_block_macro() { | ||||
let block = block! {5: Block(2)}; | ||||
assert_eq!(format!("{:?}", block), "{5: Block(2)}"); | ||||
let block = block! {13: Rev(15), 5: Block(2)}; | ||||
assert_eq!(format!("{:?}", block), "{5: Block(2), 13: Rev(15)}"); | ||||
} | ||||
#[test] | ||||
fn test_raw_block() { | ||||
let mut raw = [-1; 16]; | ||||
raw[0] = 0; | ||||
raw[1] = RawElement::to_be(15); | ||||
raw[2] = RawElement::to_be(-2); | ||||
raw[3] = RawElement::to_be(-1); | ||||
raw[4] = RawElement::to_be(-3); | ||||
let block = Block(raw); | ||||
assert_eq!(block.get(0), Element::Block(0)); | ||||
assert_eq!(block.get(1), Element::Block(15)); | ||||
assert_eq!(block.get(3), Element::None); | ||||
assert_eq!(block.get(2), Element::Rev(0)); | ||||
assert_eq!(block.get(4), Element::Rev(1)); | ||||
} | ||||
} | ||||