From cbc87b4b8046310d8f4559925332949bcf5a2815 Mon Sep 17 00:00:00 2001
From: Ben Ruijl <benruyl@gmail.com>
Date: Sat, 31 Aug 2024 09:42:53 +0200
Subject: [PATCH] Add method to merge evaluators

---
 src/evaluate.rs | 169 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 169 insertions(+)

diff --git a/src/evaluate.rs b/src/evaluate.rs
index 2977320..e3a4d49 100644
--- a/src/evaluate.rs
+++ b/src/evaluate.rs
@@ -976,6 +976,175 @@ impl<T: Default> ExpressionEvaluator<T> {
     }
 }
 
+impl<T: Default + Clone + Eq + Hash> ExpressionEvaluator<T> {
+    /// Merge evaluator `other` into `self`. The parameters must be the same.
+    pub fn merge(&mut self, mut other: Self, cpe_rounds: Option<usize>) -> Result<(), String> {
+        if self.param_count != other.param_count {
+            return Err("Parameter count is different".to_owned());
+        }
+
+        let mut constants = HashMap::default();
+
+        for (i, c) in self.stack[self.param_count..self.reserved_indices]
+            .iter()
+            .enumerate()
+        {
+            constants.insert(c.clone(), i);
+        }
+
+        let old_len = self.stack.len() - self.reserved_indices;
+
+        self.stack.truncate(self.reserved_indices);
+
+        for c in &other.stack[self.param_count..other.reserved_indices] {
+            if constants.get(c).is_none() {
+                let i = constants.len();
+                constants.insert(c.clone(), i);
+                self.stack.push(c.clone());
+            }
+        }
+
+        let new_reserved_indices = self.stack.len();
+        let mut delta = new_reserved_indices - self.reserved_indices;
+
+        // shift stack indices
+        if delta > 0 {
+            for i in &mut self.instructions {
+                match i {
+                    Instr::Add(r, a) | Instr::Mul(r, a) => {
+                        *r += delta;
+                        for aa in a {
+                            if *aa >= self.reserved_indices {
+                                *aa += delta;
+                            }
+                        }
+                    }
+                    Instr::Pow(r, b, _) | Instr::BuiltinFun(r, _, b) => {
+                        *r += delta;
+                        if *b >= self.reserved_indices {
+                            *b += delta;
+                        }
+                    }
+                    Instr::Powf(r, b, e) => {
+                        *r += delta;
+                        if *b >= self.reserved_indices {
+                            *b += delta;
+                        }
+                        if *e >= self.reserved_indices {
+                            *e += delta;
+                        }
+                    }
+                }
+            }
+
+            for x in &mut self.result_indices {
+                *x += delta;
+            }
+        }
+
+        delta = old_len + new_reserved_indices - other.reserved_indices;
+        for i in &mut other.instructions {
+            match i {
+                Instr::Add(r, a) | Instr::Mul(r, a) => {
+                    *r += delta;
+                    for aa in a {
+                        if *aa >= other.reserved_indices {
+                            *aa += delta;
+                        } else if *aa >= other.param_count {
+                            *aa = self.param_count + constants[&other.stack[*aa]];
+                        }
+                    }
+                }
+                Instr::Pow(r, b, _) | Instr::BuiltinFun(r, _, b) => {
+                    *r += delta;
+                    if *b >= other.reserved_indices {
+                        *b += delta;
+                    } else if *b >= other.param_count {
+                        *b = self.param_count + constants[&other.stack[*b]];
+                    }
+                }
+                Instr::Powf(r, b, e) => {
+                    *r += delta;
+                    if *b >= other.reserved_indices {
+                        *b += delta;
+                    } else if *b >= other.param_count {
+                        *b = self.param_count + constants[&other.stack[*b]];
+                    }
+                    if *e >= other.reserved_indices {
+                        *e += delta;
+                    } else if *e >= other.param_count {
+                        *e = self.param_count + constants[&other.stack[*e]];
+                    }
+                }
+            }
+        }
+
+        for x in &mut other.result_indices {
+            if *x >= other.reserved_indices {
+                *x += delta;
+            } else if *x >= other.param_count {
+                *x = self.param_count + constants[&other.stack[*x]];
+            }
+        }
+
+        self.instructions.extend(other.instructions.drain(..));
+        self.result_indices.extend(other.result_indices.drain(..));
+        self.reserved_indices = new_reserved_indices;
+
+        // undo the stack optimization
+        let mut unfold = HashMap::default();
+        for (index, i) in &mut self.instructions.iter_mut().enumerate() {
+            match i {
+                Instr::Add(r, a) | Instr::Mul(r, a) => {
+                    for aa in a {
+                        if *aa >= self.reserved_indices {
+                            *aa = unfold[aa];
+                        }
+                    }
+
+                    unfold.insert(*r, index + self.reserved_indices);
+                    *r = index + self.reserved_indices;
+                }
+                Instr::Pow(r, b, _) | Instr::BuiltinFun(r, _, b) => {
+                    if *b >= self.reserved_indices {
+                        *b = unfold[b];
+                    }
+                    unfold.insert(*r, index + self.reserved_indices);
+                    *r = index + self.reserved_indices;
+                }
+                Instr::Powf(r, b, e) => {
+                    if *b >= self.reserved_indices {
+                        *b = unfold[b];
+                    }
+                    if *e >= self.reserved_indices {
+                        *e = unfold[e];
+                    }
+                    unfold.insert(*r, index + self.reserved_indices);
+                    *r = index + self.reserved_indices;
+                }
+            }
+        }
+
+        for i in &mut self.result_indices {
+            *i = unfold[i];
+        }
+
+        for _ in 0..self.instructions.len() {
+            self.stack.push(T::default());
+        }
+
+        for _ in 0..cpe_rounds.unwrap_or(usize::MAX) {
+            if self.remove_common_pairs() == 0 {
+                break;
+            }
+        }
+
+        self.optimize_stack();
+
+        Ok(())
+    }
+}
+
 impl<T> ExpressionEvaluator<T> {
     pub fn optimize_stack(&mut self) {
         let mut last_use: Vec<usize> = vec![0; self.stack.len()];