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Add ensure_capacity and rename min to len

This commit is contained in:
John Kåre Alsaker 2019-04-01 22:35:13 +02:00
parent e8b3aea4d6
commit 59ff059cfc
1 changed files with 26 additions and 15 deletions
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41
src/libarena/lib.rs
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@ -161,14 +161,21 @@ impl<T> TypedArena<T> {
available_capacity_bytes >= at_least_bytes
}
/// Ensures there's enough space in the current chunk to fit `len` objects.
#[inline]
fn ensure_capacity(&self, len: usize) {
if !self.can_allocate(len) {
self.grow(len);
debug_assert!(self.can_allocate(len));
}
}
#[inline]
unsafe fn alloc_raw_slice(&self, len: usize) -> *mut T {
assert!(mem::size_of::<T>() != 0);
assert!(len != 0);
if !self.can_allocate(len) {
self.grow(len);
}
self.ensure_capacity(len);
let start_ptr = self.ptr.get();
self.ptr.set(start_ptr.add(len));
@ -203,19 +210,20 @@ impl<T> TypedArena<T> {
match size_hint {
(min, Some(max)) if min == max => {
if min == 0 {
// We know the exact number of elements the iterator will produce here
let len = min;
if len == 0 {
return &mut [];
}
if !self.can_allocate(min) {
self.grow(min);
}
self.ensure_capacity(len);
let slice = self.ptr.get();
unsafe {
let mut ptr = self.ptr.get();
for _ in 0..min {
for _ in 0..len {
// Write into uninitialized memory.
ptr::write(ptr, iter.next().unwrap());
// Advance the pointer.
@ -224,7 +232,7 @@ impl<T> TypedArena<T> {
// we destroy the correct amount
self.ptr.set(ptr);
}
slice::from_raw_parts_mut(slice, min)
slice::from_raw_parts_mut(slice, len)
}
}
_ => {
@ -239,7 +247,7 @@ impl<T> TypedArena<T> {
let len = vec.len();
let start_ptr = self.alloc_raw_slice(len);
vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
vev.set_len(0);
vec.set_len(0);
slice::from_raw_parts_mut(start_ptr, len)
}
})
@ -488,16 +496,19 @@ impl DroplessArena {
match size_hint {
(min, Some(max)) if min == max => {
if min == 0 {
// We know the exact number of elements the iterator will produce here
let len = min;
if len == 0 {
return &mut []
}
let size = min.checked_mul(mem::size_of::<T>()).unwrap();
let size = len.checked_mul(mem::size_of::<T>()).unwrap();
let mem = self.alloc_raw(size, mem::align_of::<T>()) as *mut _ as *mut T;
unsafe {
for i in 0..min {
for i in 0..len {
ptr::write(mem.offset(i as isize), iter.next().unwrap())
}
slice::from_raw_parts_mut(mem, min)
slice::from_raw_parts_mut(mem, len)
}
}
(_, _) => {
@ -515,7 +526,7 @@ impl DroplessArena {
mem::align_of::<T>()
) as *mut _ as *mut T;
vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
vev.set_len(0);
vec.set_len(0);
slice::from_raw_parts_mut(start_ptr, len)
}
})