Faster From<Vec<T>> for doubling SplitVec

Cargo.toml

@@ -19,6 +19,10 @@ orx-concurrent-iter = { version = "3.1.0", default-features = false }
 name = "serial_access"
 harness = false
 
+[[bench]]
+name = "from"
+harness = false
+
 [dev-dependencies]
 criterion = "0.7.0"
 rand = { version = "0.9.2", default-features = false }

benches/from.rs

@@ -0,0 +1,73 @@
+use criterion::{
+    BenchmarkGroup, BenchmarkId, Criterion, criterion_group, criterion_main, measurement::WallTime,
+};
+use orx_split_vec::{Doubling, Linear, Recursive, SplitVec};
+use std::hint::black_box;
+
+fn get_vec(len: usize) -> Vec<u64> {
+    let modulo = len % 3;
+    if modulo == 0 {
+        vec![len as u64; len]
+    } else if modulo == 1 {
+        vec![(len + 1) as u64; len]
+    } else {
+        vec![(len + 2) as u64; len]
+    }
+}
+
+fn doubling_from_std_vec<T>(std_vec: Vec<T>) -> SplitVec<T, Doubling> {
+    SplitVec::from(std_vec)
+}
+
+fn linear_from_std_vec<T>(std_vec: Vec<T>) -> SplitVec<T, Linear> {
+    SplitVec::from(std_vec)
+}
+
+fn recursive_from_std_vec<T>(
+    std_vec: Vec<T>
+) -> SplitVec<T, Recursive> {
+    SplitVec::from(std_vec)
+}
+
+fn test_for_type<T>(
+    group: &mut BenchmarkGroup<'_, WallTime>,
+    num_u64s: usize,
+    treatments: &[usize],
+    value: fn(usize) -> Vec<T>,
+) {
+    for n in treatments {
+        let treatment = format!("n={},elem-type=[u64;{}]", n, num_u64s);
+
+        group.bench_with_input(
+            BenchmarkId::new("doubling_from_std_vec", &treatment),
+            n,
+            |b, _| b.iter(|| doubling_from_std_vec(value(black_box(*n)))),
+        );
+
+        group.bench_with_input(
+            BenchmarkId::new("linear_from_std_vec", &treatment),
+            n,
+            |b, _| b.iter(|| linear_from_std_vec(value(black_box(*n)))),
+        );
+        group.bench_with_input(
+            BenchmarkId::new("recursive_from_std_vec", &treatment),
+            n,
+            |b, _| b.iter(|| recursive_from_std_vec(value(black_box(*n))),
+        ));
+    }
+}
+
+fn bench_from(c: &mut Criterion) {
+    let treatments = vec![1_024, 16_384, 262_144, 4_194_304];
+
+    let mut group = c.benchmark_group("from");
+
+    const N: usize = 16;
+
+    test_for_type(&mut group, N, &treatments, get_vec);
+
+    group.finish();
+}
+
+criterion_group!(benches, bench_from);
+criterion_main!(benches);

src/growth/doubling/from.rs

@@ -1,8 +1,10 @@
+use core::{cmp::min, mem::MaybeUninit, ptr::copy_nonoverlapping};
+
 use super::constants::CUMULATIVE_CAPACITIES;
-use crate::{Doubling, Fragment, SplitVec};
+use crate::{Doubling, Fragment, SplitVec, growth::doubling::constants::CAPACITIES};
 use alloc::vec::Vec;
 
-impl<T: Clone> From<Vec<T>> for SplitVec<T, Doubling> {
+impl<T> From<Vec<T>> for SplitVec<T, Doubling> {
     /// Converts a `Vec` into a `SplitVec`.
     ///
     /// # Examples
@@ -19,8 +21,9 @@ impl<T: Clone> From<Vec<T>> for SplitVec<T, Doubling> {
     /// assert_eq!(1, split_vec.fragments().len());
     /// assert!(vec_capacity <= split_vec.capacity());
     /// ```
-    fn from(value: Vec<T>) -> Self {
+    fn from(mut value: Vec<T>) -> Self {
         let len = value.len();
+        // Number of fragments to create
         let f = CUMULATIVE_CAPACITIES
             .iter()
             .enumerate()
@@ -29,26 +32,33 @@ impl<T: Clone> From<Vec<T>> for SplitVec<T, Doubling> {
             .expect("overflow");
 
         let mut fragments = Vec::with_capacity(f + 1);
-        let mut original_idx = 0;
+        let fragments_init = fragments.spare_capacity_mut();
         let mut remaining_len = len;
-        let mut curr_f = 1;
+        let mut curr_f = f;
         while remaining_len > 0 {
-            let capacity = &CUMULATIVE_CAPACITIES[curr_f];
-            let mut fragment = Fragment::new(*capacity);
-
-            let copy_len = if capacity <= &remaining_len {
-                *capacity
-            } else {
-                remaining_len
-            };
-
-            fragment.extend_from_slice(&value[original_idx..(original_idx + copy_len)]);
-
-            original_idx += copy_len;
+            curr_f -= 1;
+            let capacity = CAPACITIES[curr_f];
+            // for example, if the current fragment has a capacity of 8 but there are only 5 elements to copy,
+            // we want the copy length to only be 1
+            let copy_len = min(remaining_len - CUMULATIVE_CAPACITIES[curr_f], capacity);
             remaining_len -= copy_len;
-            fragments.push(fragment);
-            curr_f += 1;
+
+            // This is adapted from Vec::split_off, with the difference that it
+            // reserves the full capacity first to avoid extra allocations
+            let mut fragment_data = Vec::with_capacity(capacity);
+            unsafe {
+                value.set_len(remaining_len);
+                fragment_data.set_len(copy_len);
+                copy_nonoverlapping(
+                    value.as_ptr().add(remaining_len),
+                    fragment_data.as_mut_ptr(),
+                    copy_len,
+                );
+            }
+            fragments_init[curr_f] = MaybeUninit::new(Fragment::from(fragment_data));
         }
+        debug_assert_eq!(curr_f, 0);
+        unsafe { fragments.set_len(f) };
 
         Self::from_raw_parts(len, fragments, Doubling)
     }

src/growth/doubling/tests/from.rs

@@ -14,3 +14,16 @@ fn from_vec_medium() {
         validate_clone(vec, split_vec);
     }
 }
+
+#[test]
+fn from_same_as_push() {
+    for len in 0..135 {
+        let vec: Vec<_> = (0..len).collect();
+        let split_vec_from: SplitVec<_, Doubling> = vec.clone().into();
+        let mut split_vec_manual = SplitVec::new();
+        for item in vec {
+            split_vec_manual.push(item);
+        }
+        assert_eq!(split_vec_from, split_vec_manual);
+    }
+}

src/growth/recursive/from.rs

@@ -55,7 +55,7 @@ impl<T> From<SplitVec<T, Linear>> for SplitVec<T, Recursive> {
     }
 }
 
-impl<T: Clone> From<Vec<T>> for SplitVec<T, Recursive> {
+impl<T> From<Vec<T>> for SplitVec<T, Recursive> {
     /// Converts a `Vec` into a `SplitVec`.
     ///
     /// # Examples