Removes unsafe vector allocators

Note to self: before merging this, we should do a bit
more benchmarking to see how this actually affects perf.

From #163, it seems negligble.

src/backing_store/bump_table.rs

@@ -1,7 +1,7 @@
 //! A unique table based on a bump allocator and robin-hood hashing
 //! this is the primary unique table for storing all nodes
 
-use crate::{backing_store::UniqueTable, util::*};
+use crate::backing_store::UniqueTable;
 use bumpalo::Bump;
 use rustc_hash::FxHasher;
 use std::{
@@ -105,7 +105,7 @@ where
 {
     /// reserve a robin-hood table capable of holding at least `sz` elements
     pub fn new() -> BackedRobinhoodTable<'a, T> {
-        let v: Vec<HashTableElement<T>> = zero_vec(DEFAULT_SIZE);
+        let v: Vec<HashTableElement<T>> = vec![HashTableElement::default(); DEFAULT_SIZE];
 
         BackedRobinhoodTable {
             tbl: v,
@@ -135,7 +135,7 @@ where
     pub fn grow(&mut self) {
         let new_sz = (self.cap + 1).next_power_of_two();
         self.cap = new_sz;
-        let old = mem::replace(&mut self.tbl, zero_vec(new_sz));
+        let old = mem::replace(&mut self.tbl, vec![HashTableElement::default(); new_sz]);
         let c = self.cap;
         for i in old.iter() {
             propagate(&mut self.tbl, self.cap, i.clone(), (i.hash as usize) % c);

src/repr/var_order.rs

@@ -2,7 +2,7 @@
 //! in the order occur first in the BDD, starting from the root.
 //! Lower numbers occur first in the order (i.e., closer to the root)
 
-use crate::{repr::var_label::VarLabel, util};
+use crate::repr::var_label::VarLabel;
 use std::fmt::{Debug, Display};
 
 #[derive(Debug, Clone)]
@@ -19,7 +19,7 @@ impl VarOrder {
     /// Creates a new variable order (elements that occur first in the vector
     /// occur first in the order)
     pub fn new(order: Vec<VarLabel>) -> VarOrder {
-        let mut v = util::malloc_vec(order.len());
+        let mut v = vec![0; order.len()];
         let mut pos_to_var = Vec::new();
         for i in 0..order.len() {
             v[order[i].value() as usize] = i;

src/util/mod.rs

@@ -5,8 +5,6 @@ pub mod hypergraph;
 pub mod lru;
 pub mod semirings;
 
-use std::ptr;
-
 /// A generic bit-field which makes it easier to get and set
 /// bit-level fields
 #[macro_export]
@@ -30,24 +28,3 @@ macro_rules! BITFIELD {
         )+}
     }
 }
-
-/// custom allocations for zeroed vectors
-pub fn zero_vec<T>(sz: usize) -> Vec<T> {
-    let mut v: Vec<T> = Vec::with_capacity(sz);
-    unsafe {
-        let vec_ptr = v.as_mut_ptr();
-        ptr::write_bytes(vec_ptr, 0, sz);
-        v.set_len(sz);
-    }
-    v
-}
-
-/// custom allocation of a non-initialized vector
-#[allow(clippy::uninit_vec)] // intentional!
-pub fn malloc_vec<T>(sz: usize) -> Vec<T> {
-    let mut v: Vec<T> = Vec::with_capacity(sz);
-    unsafe {
-        v.set_len(sz);
-    }
-    v
-}