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io/region: return sorted Vec instead of HashMap from parse_header()

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Instead of counting and looking up indices in the HashMap, we can just
iterate over all offsets in the returned Vec.
This commit is contained in:
Matthias Schiffer 2023-01-30 19:08:51 +01:00
parent 6186a0d916
commit 8c34f74952
Signed by: neocturne
GPG key ID: 16EF3F64CB201D9C
1 changed files with 29 additions and 25 deletions
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54
src/io/region.rs
View file

@ -1,5 +1,4 @@
use std::{ use std::{
collections::HashMap,
fs::File, fs::File,
io::{prelude::*, SeekFrom}, io::{prelude::*, SeekFrom},
path::Path, path::Path,
@ -15,27 +14,35 @@ const BLOCKSIZE: usize = 4096;
#[derive(Debug)] #[derive(Debug)]
struct ChunkDesc { struct ChunkDesc {
coords: ChunkCoords, offset: u32,
len: u8, len: u8,
coords: ChunkCoords,
} }
fn parse_header(header: &ChunkArray<u32>) -> HashMap<u32, ChunkDesc> { fn parse_header(header: &ChunkArray<u32>) -> Vec<ChunkDesc> {
let mut map = HashMap::new(); let mut chunks: Vec<_> = header
.iter()
.filter_map(|(coords, &chunk)| {
let offset_len = u32::from_be(chunk);
for (coords, &chunk) in header.iter() { let offset = offset_len >> 8;
let offset_len = u32::from_be(chunk); let len = offset_len as u8;
let offset = offset_len >> 8; if offset == 0 || len == 0 {
let len = offset_len as u8; return None;
}
if offset == 0 || len == 0 { Some(ChunkDesc {
continue; offset,
} len,
coords,
})
})
.collect();
map.insert(offset, ChunkDesc { coords, len }); chunks.sort_by_key(|chunk| chunk.offset);
}
map chunks
} }
fn decode_chunk<T>(buf: &[u8]) -> Result<T> fn decode_chunk<T>(buf: &[u8]) -> Result<T>
@ -70,7 +77,7 @@ impl<R: Read + Seek> Region<R> {
{ {
let Region { mut reader } = self; let Region { mut reader } = self;
let mut chunk_map = { let chunks = {
let mut header = ChunkArray::<u32>::default(); let mut header = ChunkArray::<u32>::default();
reader reader
.read_exact(bytemuck::cast_mut::<_, [u8; BLOCKSIZE]>(&mut header.0)) .read_exact(bytemuck::cast_mut::<_, [u8; BLOCKSIZE]>(&mut header.0))
@ -79,22 +86,21 @@ impl<R: Read + Seek> Region<R> {
parse_header(&header) parse_header(&header)
}; };
let mut index = 1;
let mut seen = ChunkArray::<bool>::default(); let mut seen = ChunkArray::<bool>::default();
while !chunk_map.is_empty() { for ChunkDesc {
let Some(ChunkDesc { coords, len }) = chunk_map.remove(&index) else { offset,
index += 1; len,
continue; coords,
}; } in chunks
{
if seen[coords] { if seen[coords] {
bail!("Duplicate chunk {:?}", coords); bail!("Duplicate chunk {:?}", coords);
} }
seen[coords] = true; seen[coords] = true;
reader reader
.seek(SeekFrom::Start(index as u64 * BLOCKSIZE as u64)) .seek(SeekFrom::Start(offset as u64 * BLOCKSIZE as u64))
.context("Failed to seek chunk data")?; .context("Failed to seek chunk data")?;
let mut len_buf = [0u8; 4]; let mut len_buf = [0u8; 4];
@ -114,8 +120,6 @@ impl<R: Read + Seek> Region<R> {
.with_context(|| format!("Failed to decode data for chunk {:?}", coords))?; .with_context(|| format!("Failed to decode data for chunk {:?}", coords))?;
f(coords, chunk); f(coords, chunk);
index += len as u32;
} }
Ok(()) Ok(())