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//! Computation of clause hashes.
use std::mem::take;
use partial_ref::{partial, PartialRef};
use rustc_hash::FxHashMap as HashMap;
use varisat_formula::{Lit, Var};
use varisat_internal_proof::{lit_code_hash, lit_hash, ClauseHash};
use crate::context::{parts::*, Context};
pub struct ClauseHasher {
/// How many bits are used for storing clause hashes.
pub hash_bits: u32,
/// Changed solver names that are not yet reflected in the checkers current clause hashes.
pub buffered_solver_var_names: Vec<(Var, Option<Var>)>,
/// Does buffered_solver_var_names contain a new name?
///
/// If it contains only deletes, there is no need to rehash
pub rename_in_buffered_solver_var_names: bool,
/// Current mapping from global var names to solver var names, used for hashing.
solver_var_names: HashMap<Var, Var>,
}
impl Default for ClauseHasher {
fn default() -> ClauseHasher {
ClauseHasher {
hash_bits: 64,
buffered_solver_var_names: vec![],
rename_in_buffered_solver_var_names: false,
solver_var_names: Default::default(),
}
}
}
impl ClauseHasher {
/// Compute a clause hash of the current bit size
pub fn clause_hash(&self, lits: &[Lit]) -> ClauseHash {
let shift_bits = ClauseHash::max_value().count_ones() - self.hash_bits;
let mut hash = 0;
for &lit in lits.iter() {
match self.solver_var_names.get(&lit.var()) {
Some(var) => hash ^= lit_hash(var.lit(lit.is_positive())),
None => hash ^= lit_code_hash(lit.code() + Var::max_count() * 2),
}
}
hash >> shift_bits
}
}
/// Recompute all clause hashes if necessary
pub fn rehash(mut ctx: partial!(Context, mut ClauseHasherP, mut ClausesP)) {
let (hasher, mut ctx) = ctx.split_part_mut(ClauseHasherP);
let clauses = ctx.part_mut(ClausesP);
for (global, solver) in hasher.buffered_solver_var_names.drain(..) {
if let Some(solver) = solver {
hasher.solver_var_names.insert(global, solver);
} else {
hasher.solver_var_names.remove(&global);
}
}
hasher.rename_in_buffered_solver_var_names = false;
let mut old_clauses = take(&mut clauses.clauses);
for (_, mut candidates) in old_clauses.drain() {
for clause in candidates.drain(..) {
let hash = hasher.clause_hash(clause.lits.slice(&clauses.literal_buffer));
let candidates = clauses.clauses.entry(hash).or_default();
candidates.push(clause);
}
}
}
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