prep for debray allocation

src/prolog/indexing.rs

@@ -0,0 +1,247 @@
+use prolog::ast::*;
+
+use std::collections::{HashMap, VecDeque};
+use std::hash::Hash;
+
+#[derive(Clone, Copy)]
+enum IntIndex {
+    External(usize), Fail, Internal(usize)
+}
+
+pub struct CodeOffsets {
+    pub constants:  HashMap<Constant, ThirdLevelIndex>,
+    pub lists: ThirdLevelIndex,
+    pub structures: HashMap<(Atom, usize), ThirdLevelIndex>
+}
+
+impl CodeOffsets {
+    pub fn new() -> Self {
+        CodeOffsets {
+            constants: HashMap::new(),
+            lists: Vec::new(),
+            structures: HashMap::new()
+        }
+    }
+
+    fn cap_choice_seq_with_trust(prelude: &mut ThirdLevelIndex) {
+        prelude.last_mut().map(|instr| {
+            match instr {
+                &mut IndexedChoiceInstruction::Retry(i) =>
+                    *instr = IndexedChoiceInstruction::Trust(i),
+                _ => {}
+            };
+        });
+    }
+
+    fn add_index(is_first_index: bool, index: usize) -> IndexedChoiceInstruction {
+        if is_first_index {
+            IndexedChoiceInstruction::Try(index)
+        } else {
+            IndexedChoiceInstruction::Retry(index)
+        }
+    }
+
+    pub fn index_term(&mut self, first_arg: &Term, index: usize)
+    {
+        match first_arg {
+            &Term::Clause(_, ref name, ref terms) => {
+                let code = self.structures.entry((name.clone(), terms.len()))
+                               .or_insert(Vec::new());
+
+                let is_initial_index = code.is_empty();
+                code.push(Self::add_index(is_initial_index, index));
+            },
+            &Term::Cons(_, _, _) => {
+                let is_initial_index = self.lists.is_empty();
+                self.lists.push(Self::add_index(is_initial_index, index));
+            },
+            &Term::Constant(_, ref constant) => {
+                let code = self.constants.entry(constant.clone())
+                               .or_insert(Vec::new());
+
+                let is_initial_index = code.is_empty();
+                code.push(Self::add_index(is_initial_index, index));
+            },
+            _ => {}
+        };
+    }
+
+    fn second_level_index<Index>(indices: HashMap<Index, ThirdLevelIndex>,
+                                 prelude: &mut CodeDeque)
+                                 -> HashMap<Index, IntIndex>
+        where Index: Eq + Hash
+    {
+        let mut index_locs = HashMap::new();
+
+        for (key, mut code) in indices.into_iter() {
+            if code.len() > 1 {
+                index_locs.insert(key, IntIndex::Internal(prelude.len()));
+                Self::cap_choice_seq_with_trust(&mut code);
+                prelude.extend(code.into_iter().map(|code| Line::from(code)));
+            } else {
+                code.first().map(|i| {
+                    index_locs.insert(key, IntIndex::External(i.offset()));
+                });
+            }
+        }
+
+        index_locs
+    }
+
+    fn no_indices(&self) -> bool {
+        let no_constants = self.constants.is_empty();
+        let no_structures = self.structures.is_empty();
+        let no_lists = self.lists.is_empty();
+
+        no_constants && no_structures && no_lists
+    }
+
+    fn flatten_index<Index>(index: HashMap<Index, IntIndex>, len: usize)
+                            -> HashMap<Index, usize>
+        where Index: Eq + Hash
+    {
+        let mut flattened_index = HashMap::new();
+
+        for (key, int_index) in index.into_iter() {
+            match int_index {
+                IntIndex::External(offset) => {
+                    flattened_index.insert(key, offset + len + 1);
+                },
+                IntIndex::Internal(offset) => {
+                    flattened_index.insert(key, offset + 1);
+                },
+                _ => {}
+            };
+        }
+
+        flattened_index
+    }
+
+    fn switch_on_constant(con_ind: HashMap<Constant, ThirdLevelIndex>,
+                          prelude: &mut CodeDeque)
+                          -> IntIndex
+    {
+        let con_ind = Self::second_level_index(con_ind, prelude);
+
+        if con_ind.len() > 1 {
+            let index = Self::flatten_index(con_ind, prelude.len());
+            let instr = IndexingInstruction::SwitchOnConstant(index.len(), index);
+
+            prelude.push_front(Line::from(instr));
+
+            IntIndex::Internal(1)
+        } else {
+            con_ind.values().next()
+                   .map(|i| *i)
+                   .unwrap_or(IntIndex::Fail)
+        }
+    }
+
+    fn switch_on_list(mut lists: ThirdLevelIndex, prelude: &mut CodeDeque) -> IntIndex
+    {
+        if lists.len() > 1 {
+            Self::cap_choice_seq_with_trust(&mut lists);
+            prelude.extend(lists.into_iter().map(|i| Line::from(i)));
+            IntIndex::Internal(0)
+        } else {
+            lists.first()
+                 .map(|i| IntIndex::External(i.offset()))
+                 .unwrap_or(IntIndex::Fail)
+        }
+    }
+
+    fn switch_on_structure(str_ind: HashMap<(Atom, usize), ThirdLevelIndex>,
+                           prelude: &mut CodeDeque)
+                           -> IntIndex
+    {
+        let str_ind = Self::second_level_index(str_ind, prelude);
+
+        if str_ind.len() > 1 {
+            let index = Self::flatten_index(str_ind, prelude.len());
+            let instr = IndexingInstruction::SwitchOnStructure(index.len(), index);
+
+            prelude.push_front(Line::from(instr));
+
+            IntIndex::Internal(1)
+        } else {
+            str_ind.values().next()
+                   .map(|i| *i)
+                   .unwrap_or(IntIndex::Fail)
+        }
+    }
+
+
+    fn switch_on_str_offset_from(str_loc: IntIndex, prelude_len: usize, con_loc: IntIndex)
+                                 -> usize
+    {
+        match str_loc {
+            IntIndex::External(o) => o + prelude_len + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(_) => match con_loc {
+                IntIndex::Internal(_) => 2,
+                _ => 1
+            }
+        }
+    }
+
+    fn switch_on_con_offset_from(con_loc: IntIndex, prelude_len: usize) -> usize
+    {
+        match con_loc {
+            IntIndex::External(offset) => offset + prelude_len + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(offset) => offset,
+        }
+    }
+
+    fn switch_on_lst_offset_from(lst_loc: IntIndex, prelude_len: usize, lst_offset: usize)
+                                 -> usize
+    {
+        match lst_loc {
+            IntIndex::External(o) => o + prelude_len + 1,
+            IntIndex::Fail => 0,
+            IntIndex::Internal(_) => prelude_len - lst_offset + 1
+        }
+    }
+
+    pub fn add_indices(self, code: &mut Code, mut code_body: Code)
+    {
+        if self.no_indices() {
+            *code = code_body;
+            return;
+        }
+
+        let mut prelude = VecDeque::new();
+
+        let lst_loc = Self::switch_on_list(self.lists, &mut prelude);
+        let lst_offset = prelude.len();
+
+        let str_loc = Self::switch_on_structure(self.structures, &mut prelude);
+        let con_loc = Self::switch_on_constant(self.constants, &mut prelude);
+
+        let prelude_length = prelude.len();
+
+        for (index, line) in prelude.iter_mut().enumerate() {
+            match line {
+                  &mut Line::IndexedChoice(IndexedChoiceInstruction::Try(ref mut i))
+                | &mut Line::IndexedChoice(IndexedChoiceInstruction::Retry(ref mut i))
+                | &mut Line::IndexedChoice(IndexedChoiceInstruction::Trust(ref mut i)) =>
+                    *i += prelude_length - index,
+                _ => {}
+            }
+        }
+
+        let str_loc = Self::switch_on_str_offset_from(str_loc, prelude.len(), con_loc);
+        let con_loc = Self::switch_on_con_offset_from(con_loc, prelude.len());
+        let lst_loc = Self::switch_on_lst_offset_from(lst_loc, prelude.len(), lst_offset);
+
+        let switch_instr = IndexingInstruction::SwitchOnTerm(prelude.len() + 1,
+                                                             con_loc,
+                                                             lst_loc,
+                                                             str_loc);
+
+        prelude.push_front(Line::from(switch_instr));
+
+        *code = Vec::from(prelude);
+        code.append(&mut code_body);
+    }
+}