| //! A module for propagating forward dataflow information. The analysis |
| //! assumes that the items to be propagated can be represented as bits |
| //! and thus uses bitvectors. Your job is simply to specify the so-called |
| //! GEN and KILL bits for each expression. |
| |
| use rustc::cfg; |
| use rustc::cfg::CFGIndex; |
| use rustc::ty::TyCtxt; |
| use std::io; |
| use std::mem; |
| use std::usize; |
| use syntax::print::pprust::PrintState; |
| use log::debug; |
| |
| use rustc_data_structures::graph::implementation::OUTGOING; |
| |
| use rustc::util::nodemap::FxHashMap; |
| use rustc::hir; |
| use rustc::hir::intravisit; |
| use rustc::hir::print as pprust; |
| |
| #[derive(Copy, Clone, Debug)] |
| pub enum EntryOrExit { |
| Entry, |
| Exit, |
| } |
| |
| #[derive(Clone)] |
| pub struct DataFlowContext<'tcx, O> { |
| tcx: TyCtxt<'tcx>, |
| |
| /// a name for the analysis using this dataflow instance |
| analysis_name: &'static str, |
| |
| /// the data flow operator |
| oper: O, |
| |
| /// number of bits to propagate per id |
| bits_per_id: usize, |
| |
| /// number of words we will use to store bits_per_id. |
| /// equal to bits_per_id/usize::BITS rounded up. |
| words_per_id: usize, |
| |
| // mapping from node to cfg node index |
| // FIXME (#6298): Shouldn't this go with CFG? |
| local_id_to_index: FxHashMap<hir::ItemLocalId, Vec<CFGIndex>>, |
| |
| // Bit sets per cfg node. The following three fields (`gens`, `kills`, |
| // and `on_entry`) all have the same structure. For each id in |
| // `id_range`, there is a range of words equal to `words_per_id`. |
| // So, to access the bits for any given id, you take a slice of |
| // the full vector (see the method `compute_id_range()`). |
| /// bits generated as we exit the cfg node. Updated by `add_gen()`. |
| gens: Vec<usize>, |
| |
| /// bits killed as we exit the cfg node, or non-locally jump over |
| /// it. Updated by `add_kill(KillFrom::ScopeEnd)`. |
| scope_kills: Vec<usize>, |
| |
| /// bits killed as we exit the cfg node directly; if it is jumped |
| /// over, e.g., via `break`, the kills are not reflected in the |
| /// jump's effects. Updated by `add_kill(KillFrom::Execution)`. |
| action_kills: Vec<usize>, |
| |
| /// bits that are valid on entry to the cfg node. Updated by |
| /// `propagate()`. |
| on_entry: Vec<usize>, |
| } |
| |
| pub trait BitwiseOperator { |
| /// Joins two predecessor bits together, typically either `|` or `&` |
| fn join(&self, succ: usize, pred: usize) -> usize; |
| } |
| |
| /// Parameterization for the precise form of data flow that is used. |
| pub trait DataFlowOperator : BitwiseOperator { |
| /// Specifies the initial value for each bit in the `on_entry` set |
| fn initial_value(&self) -> bool; |
| } |
| |
| struct PropagationContext<'a, 'tcx, O> { |
| dfcx: &'a mut DataFlowContext<'tcx, O>, |
| changed: bool, |
| } |
| |
| fn get_cfg_indices<'a>(id: hir::ItemLocalId, |
| index: &'a FxHashMap<hir::ItemLocalId, Vec<CFGIndex>>) |
| -> &'a [CFGIndex] { |
| index.get(&id).map_or(&[], |v| &v[..]) |
| } |
| |
| impl<'tcx, O: DataFlowOperator> DataFlowContext<'tcx, O> { |
| fn has_bitset_for_local_id(&self, n: hir::ItemLocalId) -> bool { |
| assert!(n != hir::DUMMY_ITEM_LOCAL_ID); |
| self.local_id_to_index.contains_key(&n) |
| } |
| } |
| |
| impl<'tcx, O: DataFlowOperator> pprust::PpAnn for DataFlowContext<'tcx, O> { |
| fn nested(&self, state: &mut pprust::State<'_>, nested: pprust::Nested) -> io::Result<()> { |
| pprust::PpAnn::nested(self.tcx.hir(), state, nested) |
| } |
| fn pre(&self, |
| ps: &mut pprust::State<'_>, |
| node: pprust::AnnNode<'_>) -> io::Result<()> { |
| let id = match node { |
| pprust::AnnNode::Name(_) => return Ok(()), |
| pprust::AnnNode::Expr(expr) => expr.hir_id.local_id, |
| pprust::AnnNode::Block(blk) => blk.hir_id.local_id, |
| pprust::AnnNode::Item(_) | |
| pprust::AnnNode::SubItem(_) => return Ok(()), |
| pprust::AnnNode::Pat(pat) => pat.hir_id.local_id |
| }; |
| |
| if !self.has_bitset_for_local_id(id) { |
| return Ok(()); |
| } |
| |
| assert!(self.bits_per_id > 0); |
| let indices = get_cfg_indices(id, &self.local_id_to_index); |
| for &cfgidx in indices { |
| let (start, end) = self.compute_id_range(cfgidx); |
| let on_entry = &self.on_entry[start.. end]; |
| let entry_str = bits_to_string(on_entry); |
| |
| let gens = &self.gens[start.. end]; |
| let gens_str = if gens.iter().any(|&u| u != 0) { |
| format!(" gen: {}", bits_to_string(gens)) |
| } else { |
| String::new() |
| }; |
| |
| let action_kills = &self.action_kills[start .. end]; |
| let action_kills_str = if action_kills.iter().any(|&u| u != 0) { |
| format!(" action_kill: {}", bits_to_string(action_kills)) |
| } else { |
| String::new() |
| }; |
| |
| let scope_kills = &self.scope_kills[start .. end]; |
| let scope_kills_str = if scope_kills.iter().any(|&u| u != 0) { |
| format!(" scope_kill: {}", bits_to_string(scope_kills)) |
| } else { |
| String::new() |
| }; |
| |
| ps.synth_comment( |
| format!("id {}: {}{}{}{}", id.as_usize(), entry_str, |
| gens_str, action_kills_str, scope_kills_str))?; |
| ps.s.space()?; |
| } |
| Ok(()) |
| } |
| } |
| |
| fn build_local_id_to_index(body: Option<&hir::Body>, |
| cfg: &cfg::CFG) |
| -> FxHashMap<hir::ItemLocalId, Vec<CFGIndex>> { |
| let mut index = FxHashMap::default(); |
| |
| // FIXME(#15020) Would it be better to fold formals from decl |
| // into cfg itself? i.e., introduce a fn-based flow-graph in |
| // addition to the current block-based flow-graph, rather than |
| // have to put traversals like this here? |
| if let Some(body) = body { |
| add_entries_from_fn_body(&mut index, body, cfg.entry); |
| } |
| |
| cfg.graph.each_node(|node_idx, node| { |
| if let cfg::CFGNodeData::AST(id) = node.data { |
| index.entry(id).or_default().push(node_idx); |
| } |
| true |
| }); |
| |
| return index; |
| |
| /// Adds mappings from the ast nodes for the formal bindings to |
| /// the entry-node in the graph. |
| fn add_entries_from_fn_body(index: &mut FxHashMap<hir::ItemLocalId, Vec<CFGIndex>>, |
| body: &hir::Body, |
| entry: CFGIndex) { |
| use rustc::hir::intravisit::Visitor; |
| |
| struct Formals<'a> { |
| entry: CFGIndex, |
| index: &'a mut FxHashMap<hir::ItemLocalId, Vec<CFGIndex>>, |
| } |
| let mut formals = Formals { entry: entry, index: index }; |
| for arg in &body.arguments { |
| formals.visit_pat(&arg.pat); |
| } |
| impl<'a, 'v> Visitor<'v> for Formals<'a> { |
| fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'v> { |
| intravisit::NestedVisitorMap::None |
| } |
| |
| fn visit_pat(&mut self, p: &hir::Pat) { |
| self.index.entry(p.hir_id.local_id).or_default().push(self.entry); |
| intravisit::walk_pat(self, p) |
| } |
| } |
| } |
| } |
| |
| /// Flag used by `add_kill` to indicate whether the provided kill |
| /// takes effect only when control flows directly through the node in |
| /// question, or if the kill's effect is associated with any |
| /// control-flow directly through or indirectly over the node. |
| #[derive(Copy, Clone, PartialEq, Debug)] |
| pub enum KillFrom { |
| /// A `ScopeEnd` kill is one that takes effect when any control |
| /// flow goes over the node. A kill associated with the end of the |
| /// scope of a variable declaration `let x;` is an example of a |
| /// `ScopeEnd` kill. |
| ScopeEnd, |
| |
| /// An `Execution` kill is one that takes effect only when control |
| /// flow goes through the node to completion. A kill associated |
| /// with an assignment statement `x = expr;` is an example of an |
| /// `Execution` kill. |
| Execution, |
| } |
| |
| impl<'tcx, O: DataFlowOperator> DataFlowContext<'tcx, O> { |
| pub fn new( |
| tcx: TyCtxt<'tcx>, |
| analysis_name: &'static str, |
| body: Option<&hir::Body>, |
| cfg: &cfg::CFG, |
| oper: O, |
| bits_per_id: usize, |
| ) -> DataFlowContext<'tcx, O> { |
| let usize_bits = mem::size_of::<usize>() * 8; |
| let words_per_id = (bits_per_id + usize_bits - 1) / usize_bits; |
| let num_nodes = cfg.graph.all_nodes().len(); |
| |
| debug!("DataFlowContext::new(analysis_name: {}, \ |
| bits_per_id={}, words_per_id={}) \ |
| num_nodes: {}", |
| analysis_name, bits_per_id, words_per_id, |
| num_nodes); |
| |
| let entry = if oper.initial_value() { usize::MAX } else {0}; |
| |
| let zeroes = vec![0; num_nodes * words_per_id]; |
| let gens = zeroes.clone(); |
| let kills1 = zeroes.clone(); |
| let kills2 = zeroes; |
| let on_entry = vec![entry; num_nodes * words_per_id]; |
| |
| let local_id_to_index = build_local_id_to_index(body, cfg); |
| |
| DataFlowContext { |
| tcx, |
| analysis_name, |
| words_per_id, |
| local_id_to_index, |
| bits_per_id, |
| oper, |
| gens, |
| action_kills: kills1, |
| scope_kills: kills2, |
| on_entry, |
| } |
| } |
| |
| pub fn add_gen(&mut self, id: hir::ItemLocalId, bit: usize) { |
| //! Indicates that `id` generates `bit` |
| debug!("{} add_gen(id={:?}, bit={})", |
| self.analysis_name, id, bit); |
| assert!(self.local_id_to_index.contains_key(&id)); |
| assert!(self.bits_per_id > 0); |
| |
| let indices = get_cfg_indices(id, &self.local_id_to_index); |
| for &cfgidx in indices { |
| let (start, end) = self.compute_id_range(cfgidx); |
| let gens = &mut self.gens[start.. end]; |
| set_bit(gens, bit); |
| } |
| } |
| |
| pub fn add_kill(&mut self, kind: KillFrom, id: hir::ItemLocalId, bit: usize) { |
| //! Indicates that `id` kills `bit` |
| debug!("{} add_kill(id={:?}, bit={})", |
| self.analysis_name, id, bit); |
| assert!(self.local_id_to_index.contains_key(&id)); |
| assert!(self.bits_per_id > 0); |
| |
| let indices = get_cfg_indices(id, &self.local_id_to_index); |
| for &cfgidx in indices { |
| let (start, end) = self.compute_id_range(cfgidx); |
| let kills = match kind { |
| KillFrom::Execution => &mut self.action_kills[start.. end], |
| KillFrom::ScopeEnd => &mut self.scope_kills[start.. end], |
| }; |
| set_bit(kills, bit); |
| } |
| } |
| |
| fn apply_gen_kill(&self, cfgidx: CFGIndex, bits: &mut [usize]) { |
| //! Applies the gen and kill sets for `cfgidx` to `bits` |
| debug!("{} apply_gen_kill(cfgidx={:?}, bits={}) [before]", |
| self.analysis_name, cfgidx, mut_bits_to_string(bits)); |
| assert!(self.bits_per_id > 0); |
| |
| let (start, end) = self.compute_id_range(cfgidx); |
| let gens = &self.gens[start.. end]; |
| bitwise(bits, gens, &Union); |
| let kills = &self.action_kills[start.. end]; |
| bitwise(bits, kills, &Subtract); |
| let kills = &self.scope_kills[start.. end]; |
| bitwise(bits, kills, &Subtract); |
| |
| debug!("{} apply_gen_kill(cfgidx={:?}, bits={}) [after]", |
| self.analysis_name, cfgidx, mut_bits_to_string(bits)); |
| } |
| |
| fn compute_id_range(&self, cfgidx: CFGIndex) -> (usize, usize) { |
| let n = cfgidx.node_id(); |
| let start = n * self.words_per_id; |
| let end = start + self.words_per_id; |
| |
| assert!(start < self.gens.len()); |
| assert!(end <= self.gens.len()); |
| assert!(self.gens.len() == self.action_kills.len()); |
| assert!(self.gens.len() == self.scope_kills.len()); |
| assert!(self.gens.len() == self.on_entry.len()); |
| |
| (start, end) |
| } |
| |
| |
| pub fn each_bit_on_entry<F>(&self, id: hir::ItemLocalId, mut f: F) -> bool where |
| F: FnMut(usize) -> bool, |
| { |
| //! Iterates through each bit that is set on entry to `id`. |
| //! Only useful after `propagate()` has been called. |
| if !self.has_bitset_for_local_id(id) { |
| return true; |
| } |
| let indices = get_cfg_indices(id, &self.local_id_to_index); |
| for &cfgidx in indices { |
| if !self.each_bit_for_node(EntryOrExit::Entry, cfgidx, |i| f(i)) { |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| pub fn each_bit_for_node<F>(&self, e: EntryOrExit, cfgidx: CFGIndex, f: F) -> bool where |
| F: FnMut(usize) -> bool, |
| { |
| //! Iterates through each bit that is set on entry/exit to `cfgidx`. |
| //! Only useful after `propagate()` has been called. |
| |
| if self.bits_per_id == 0 { |
| // Skip the surprisingly common degenerate case. (Note |
| // compute_id_range requires self.words_per_id > 0.) |
| return true; |
| } |
| |
| let (start, end) = self.compute_id_range(cfgidx); |
| let on_entry = &self.on_entry[start.. end]; |
| let temp_bits; |
| let slice = match e { |
| EntryOrExit::Entry => on_entry, |
| EntryOrExit::Exit => { |
| let mut t = on_entry.to_vec(); |
| self.apply_gen_kill(cfgidx, &mut t); |
| temp_bits = t; |
| &temp_bits[..] |
| } |
| }; |
| debug!("{} each_bit_for_node({:?}, cfgidx={:?}) bits={}", |
| self.analysis_name, e, cfgidx, bits_to_string(slice)); |
| self.each_bit(slice, f) |
| } |
| |
| pub fn each_gen_bit<F>(&self, id: hir::ItemLocalId, mut f: F) -> bool where |
| F: FnMut(usize) -> bool, |
| { |
| //! Iterates through each bit in the gen set for `id`. |
| if !self.has_bitset_for_local_id(id) { |
| return true; |
| } |
| |
| if self.bits_per_id == 0 { |
| // Skip the surprisingly common degenerate case. (Note |
| // compute_id_range requires self.words_per_id > 0.) |
| return true; |
| } |
| |
| let indices = get_cfg_indices(id, &self.local_id_to_index); |
| for &cfgidx in indices { |
| let (start, end) = self.compute_id_range(cfgidx); |
| let gens = &self.gens[start.. end]; |
| debug!("{} each_gen_bit(id={:?}, gens={})", |
| self.analysis_name, id, bits_to_string(gens)); |
| if !self.each_bit(gens, |i| f(i)) { |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| fn each_bit<F>(&self, words: &[usize], mut f: F) -> bool where |
| F: FnMut(usize) -> bool, |
| { |
| //! Helper for iterating over the bits in a bit set. |
| //! Returns false on the first call to `f` that returns false; |
| //! if all calls to `f` return true, then returns true. |
| |
| let usize_bits = mem::size_of::<usize>() * 8; |
| for (word_index, &word) in words.iter().enumerate() { |
| if word != 0 { |
| let base_index = word_index * usize_bits; |
| for offset in 0..usize_bits { |
| let bit = 1 << offset; |
| if (word & bit) != 0 { |
| // N.B., we round up the total number of bits |
| // that we store in any given bit set so that |
| // it is an even multiple of usize::BITS. This |
| // means that there may be some stray bits at |
| // the end that do not correspond to any |
| // actual value. So before we callback, check |
| // whether the bit_index is greater than the |
| // actual value the user specified and stop |
| // iterating if so. |
| let bit_index = base_index + offset as usize; |
| if bit_index >= self.bits_per_id { |
| return true; |
| } else if !f(bit_index) { |
| return false; |
| } |
| } |
| } |
| } |
| } |
| return true; |
| } |
| |
| pub fn add_kills_from_flow_exits(&mut self, cfg: &cfg::CFG) { |
| //! Whenever you have a `break` or `continue` statement, flow |
| //! exits through any number of enclosing scopes on its way to |
| //! the new destination. This function infers the kill bits of |
| //! those control operators based on the kill bits associated |
| //! with those scopes. |
| //! |
| //! This is usually called (if it is called at all), after |
| //! all add_gen and add_kill calls, but before propagate. |
| |
| debug!("{} add_kills_from_flow_exits", self.analysis_name); |
| if self.bits_per_id == 0 { |
| // Skip the surprisingly common degenerate case. (Note |
| // compute_id_range requires self.words_per_id > 0.) |
| return; |
| } |
| cfg.graph.each_edge(|_edge_index, edge| { |
| let flow_exit = edge.source(); |
| let (start, end) = self.compute_id_range(flow_exit); |
| let mut orig_kills = self.scope_kills[start.. end].to_vec(); |
| |
| let mut changed = false; |
| for &id in &edge.data.exiting_scopes { |
| let opt_cfg_idx = self.local_id_to_index.get(&id); |
| match opt_cfg_idx { |
| Some(indices) => { |
| for &cfg_idx in indices { |
| let (start, end) = self.compute_id_range(cfg_idx); |
| let kills = &self.scope_kills[start.. end]; |
| if bitwise(&mut orig_kills, kills, &Union) { |
| debug!("scope exits: scope id={:?} \ |
| (node={:?} of {:?}) added killset: {}", |
| id, cfg_idx, indices, |
| bits_to_string(kills)); |
| changed = true; |
| } |
| } |
| } |
| None => { |
| debug!("{} add_kills_from_flow_exits flow_exit={:?} \ |
| no cfg_idx for exiting_scope={:?}", |
| self.analysis_name, flow_exit, id); |
| } |
| } |
| } |
| |
| if changed { |
| let bits = &mut self.scope_kills[start.. end]; |
| debug!("{} add_kills_from_flow_exits flow_exit={:?} bits={} [before]", |
| self.analysis_name, flow_exit, mut_bits_to_string(bits)); |
| bits.copy_from_slice(&orig_kills[..]); |
| debug!("{} add_kills_from_flow_exits flow_exit={:?} bits={} [after]", |
| self.analysis_name, flow_exit, mut_bits_to_string(bits)); |
| } |
| true |
| }); |
| } |
| } |
| |
| // N.B. `Clone + 'static` only needed for pretty printing. |
| impl<'tcx, O: DataFlowOperator + Clone + 'static> DataFlowContext<'tcx, O> { |
| pub fn propagate(&mut self, cfg: &cfg::CFG, body: &hir::Body) { |
| //! Performs the data flow analysis. |
| |
| if self.bits_per_id == 0 { |
| // Optimize the surprisingly common degenerate case. |
| return; |
| } |
| |
| { |
| let words_per_id = self.words_per_id; |
| let mut propcx = PropagationContext { |
| dfcx: &mut *self, |
| changed: true |
| }; |
| |
| let nodes_po = cfg.graph.nodes_in_postorder(OUTGOING, cfg.entry); |
| let mut temp = vec![0; words_per_id]; |
| let mut num_passes = 0; |
| while propcx.changed { |
| num_passes += 1; |
| propcx.changed = false; |
| propcx.reset(&mut temp); |
| propcx.walk_cfg(cfg, &nodes_po, &mut temp); |
| } |
| debug!("finished in {} iterations", num_passes); |
| } |
| |
| debug!("Dataflow result for {}:", self.analysis_name); |
| debug!("{}", pprust::to_string(self, |s| { |
| s.cbox(pprust::indent_unit)?; |
| s.ibox(0)?; |
| s.print_expr(&body.value) |
| })); |
| } |
| } |
| |
| impl<O: DataFlowOperator> PropagationContext<'_, 'tcx, O> { |
| fn walk_cfg(&mut self, |
| cfg: &cfg::CFG, |
| nodes_po: &[CFGIndex], |
| in_out: &mut [usize]) { |
| debug!("DataFlowContext::walk_cfg(in_out={}) {}", |
| bits_to_string(in_out), self.dfcx.analysis_name); |
| assert!(self.dfcx.bits_per_id > 0); |
| |
| // Iterate over nodes in reverse post-order. |
| for &node_index in nodes_po.iter().rev() { |
| let node = cfg.graph.node(node_index); |
| debug!("DataFlowContext::walk_cfg idx={:?} id={:?} begin in_out={}", |
| node_index, node.data.id(), bits_to_string(in_out)); |
| |
| let (start, end) = self.dfcx.compute_id_range(node_index); |
| |
| // Initialize local bitvector with state on-entry. |
| in_out.copy_from_slice(&self.dfcx.on_entry[start.. end]); |
| |
| // Compute state on-exit by applying transfer function to |
| // state on-entry. |
| self.dfcx.apply_gen_kill(node_index, in_out); |
| |
| // Propagate state on-exit from node into its successors. |
| self.propagate_bits_into_graph_successors_of(in_out, cfg, node_index); |
| } |
| } |
| |
| fn reset(&mut self, bits: &mut [usize]) { |
| let e = if self.dfcx.oper.initial_value() {usize::MAX} else {0}; |
| for b in bits { |
| *b = e; |
| } |
| } |
| |
| fn propagate_bits_into_graph_successors_of(&mut self, |
| pred_bits: &[usize], |
| cfg: &cfg::CFG, |
| cfgidx: CFGIndex) { |
| for (_, edge) in cfg.graph.outgoing_edges(cfgidx) { |
| self.propagate_bits_into_entry_set_for(pred_bits, edge); |
| } |
| } |
| |
| fn propagate_bits_into_entry_set_for(&mut self, |
| pred_bits: &[usize], |
| edge: &cfg::CFGEdge) { |
| let source = edge.source(); |
| let cfgidx = edge.target(); |
| debug!("{} propagate_bits_into_entry_set_for(pred_bits={}, {:?} to {:?})", |
| self.dfcx.analysis_name, bits_to_string(pred_bits), source, cfgidx); |
| assert!(self.dfcx.bits_per_id > 0); |
| |
| let (start, end) = self.dfcx.compute_id_range(cfgidx); |
| let changed = { |
| // (scoping mutable borrow of self.dfcx.on_entry) |
| let on_entry = &mut self.dfcx.on_entry[start.. end]; |
| bitwise(on_entry, pred_bits, &self.dfcx.oper) |
| }; |
| if changed { |
| debug!("{} changed entry set for {:?} to {}", |
| self.dfcx.analysis_name, cfgidx, |
| bits_to_string(&self.dfcx.on_entry[start.. end])); |
| self.changed = true; |
| } |
| } |
| } |
| |
| fn mut_bits_to_string(words: &mut [usize]) -> String { |
| bits_to_string(words) |
| } |
| |
| fn bits_to_string(words: &[usize]) -> String { |
| let mut result = String::new(); |
| let mut sep = '['; |
| |
| // Note: this is a little endian printout of bytes. |
| |
| for &word in words { |
| let mut v = word; |
| for _ in 0..mem::size_of::<usize>() { |
| result.push(sep); |
| result.push_str(&format!("{:02x}", v & 0xFF)); |
| v >>= 8; |
| sep = '-'; |
| } |
| } |
| result.push(']'); |
| return result |
| } |
| |
| #[inline] |
| fn bitwise<Op: BitwiseOperator>(out_vec: &mut [usize], |
| in_vec: &[usize], |
| op: &Op) -> bool { |
| assert_eq!(out_vec.len(), in_vec.len()); |
| let mut changed = false; |
| for (out_elt, in_elt) in out_vec.iter_mut().zip(in_vec) { |
| let old_val = *out_elt; |
| let new_val = op.join(old_val, *in_elt); |
| *out_elt = new_val; |
| changed |= old_val != new_val; |
| } |
| changed |
| } |
| |
| fn set_bit(words: &mut [usize], bit: usize) -> bool { |
| debug!("set_bit: words={} bit={}", |
| mut_bits_to_string(words), bit_str(bit)); |
| let usize_bits = mem::size_of::<usize>() * 8; |
| let word = bit / usize_bits; |
| let bit_in_word = bit % usize_bits; |
| let bit_mask = 1 << bit_in_word; |
| debug!("word={} bit_in_word={} bit_mask={}", word, bit_in_word, bit_mask); |
| let oldv = words[word]; |
| let newv = oldv | bit_mask; |
| words[word] = newv; |
| oldv != newv |
| } |
| |
| fn bit_str(bit: usize) -> String { |
| let byte = bit >> 3; |
| let lobits = 1 << (bit & 0b111); |
| format!("[{}:{}-{:02x}]", bit, byte, lobits) |
| } |
| |
| struct Union; |
| impl BitwiseOperator for Union { |
| fn join(&self, a: usize, b: usize) -> usize { a | b } |
| } |
| struct Subtract; |
| impl BitwiseOperator for Subtract { |
| fn join(&self, a: usize, b: usize) -> usize { a & !b } |
| } |