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use std::collections::BTreeSet; use std::io::{Seek, SeekFrom, Write}; use std::mem; use super::*; #[derive(Copy, Clone, Debug)] struct HashPos(Hash, u32); impl HashPos { #[inline] fn distance(self, tlen: usize, pos: usize) -> usize { let startslot = self.0.slot(tlen); pos.checked_sub(startslot) .unwrap_or_else(|| pos + tlen - startslot) } } const FILLFACTOR: usize = 2; pub struct Writer<T> { file: T, pos: u64, tables: Vec<Vec<HashPos>>, header: [PosLen; ENTRIES], } impl<T> Writer<T> where T: Write + Seek, { pub fn new(mut file: T) -> Result<Self, std::io::Error> { let pos = (ENTRIES * PAIR_SIZE) as u64; let tables = vec![Vec::new(); ENTRIES]; file.seek(SeekFrom::Start(pos))?; Ok(Writer { file, pos, tables, header: [PosLen { pos: 0, len: 0 }; ENTRIES], }) } fn write_kv(&mut self, k: &[u8], v: &[u8]) -> Result<(), std::io::Error> { self.file.write_all(&(k.len() as u32).to_le_bytes())?; self.file.write_all(&(v.len() as u32).to_le_bytes())?; self.file.write_all(k)?; self.file.write_all(v)?; self.pos += (PAIR_SIZE + k.len() + v.len()) as u64; Ok(()) } pub fn write(&mut self, k: &[u8], v: &[u8]) -> Result<(), std::io::Error> { let hash = Hash::new(k); let tableidx = hash.table(); self.tables[tableidx].push(HashPos(hash, self.pos as u32)); self.write_kv(k, v)?; Ok(()) } fn write_header(&mut self) -> Result<(), std::io::Error> { self.file.seek(SeekFrom::Start(0))?; for header in self.header.iter() { self.file.write_all(&(header.pos as u32).to_le_bytes())?; self.file.write_all(&(header.len as u32).to_le_bytes())?; } Ok(()) } fn finish_generic<F>(mut self, fill: F) -> Result<T, std::io::Error> where F: Fn(&[HashPos], &mut Vec<HashPos>), { let mut tout = Vec::new(); for (i, table) in self.tables.iter().enumerate() { fill(&table, &mut tout); self.header[i] = PosLen { pos: self.pos as usize, len: tout.len(), }; for row in &tout { let hash: u32 = row.0.into(); self.file.write_all(&hash.to_le_bytes())?; self.file.write_all(&row.1.to_le_bytes())?; } self.pos += (PAIR_SIZE * tout.len()) as u64; } self.write_header()?; self.file.flush()?; Ok(self.file) } pub fn finish(self) -> Result<T, std::io::Error> { self.finish_robinhood() } pub fn finish_naive(self) -> Result<T, std::io::Error> { self.finish_generic(fill_table_naive) } pub fn finish_btree(self) -> Result<T, std::io::Error> { self.finish_generic(fill_table_btree) } pub fn finish_robinhood(self) -> Result<T, std::io::Error> { self.finish_generic(fill_table_robinhood) } pub fn into_file(self) -> T { self.file } pub fn file(&self) -> &T { &self.file } } fn fill_table_naive(input: &[HashPos], output: &mut Vec<HashPos>) { let tlen = input.len() * FILLFACTOR; output.clear(); output.resize(tlen, HashPos(Hash(0), 0)); for hp in input { let (left, right) = output.split_at_mut(hp.0.slot(tlen)); for slot in right.iter_mut().chain(left.iter_mut()) { if slot.1 == 0 { *slot = *hp; break; } } } } fn fill_table_btree(input: &[HashPos], output: &mut Vec<HashPos>) { let mut cache = BTreeSet::new(); let tlen = input.len() * FILLFACTOR; output.clear(); output.resize(tlen, HashPos(Hash(0), 0)); cache.extend(0..tlen); for hp in input { let startpos = hp.0.slot(tlen); let idx = *cache .range(startpos..) .chain(cache.range(0..startpos)) .next() .unwrap(); cache.take(&idx); debug_assert_eq!(output[idx].1, 0); output[idx] = *hp; } } fn fill_table_robinhood(input: &[HashPos], output: &mut Vec<HashPos>) { let tlen = input.len() * FILLFACTOR; output.clear(); output.resize(tlen, HashPos(Hash(0), 0)); for mut hp in input.iter().cloned() { let startslot = hp.0.slot(tlen); let (left, right) = output.split_at_mut(startslot); let mut slotnum = startslot; let mut distance = 0; for slot in right.iter_mut().chain(left.iter_mut()) { if slot.1 == 0 { *slot = hp; break; } else if slot.distance(tlen, slotnum) < distance { mem::swap(slot, &mut hp); distance = hp.distance(tlen, slotnum); } distance += 1; slotnum = (slotnum + 1) % tlen; } } }