#![feature(unique)]
#![feature(const_fn)]
#![no_std]
#[cfg(test)]
#[macro_use]
extern crate std;
use hole::HoleList;
mod hole;
#[cfg(test)]
mod test;
/// A fixed size heap backed by a linked list of free memory blocks.
pub struct Heap {
bottom: usize,
top: usize,
holes: HoleList,
}
impl Heap {
/// Creates an empty heap. All allocate calls will return `None`.
pub const fn empty() -> Heap {
Heap {
top: 0,
bottom: 0,
holes: HoleList::empty(),
}
}
/// Creates a new heap with the given `bottom` and `top`. Both addresses must be valid and the
/// memory in the `[heap_bottom, heap_top)` range must not be used for anything else. This
/// function is unsafe because it can cause undefined behavior if the given addresses are
/// invalid.
pub unsafe fn new(heap_bottom: usize, heap_top: usize) -> Heap {
Heap {
bottom: heap_bottom,
top: heap_top,
holes: HoleList::new(heap_bottom, heap_top - heap_bottom),
}
}
/// Allocates a chunk of the given size with the given alignment. Returns a pointer to the
/// beginning of that chunk if it was successful. Else it returns `None`.
/// This function scans the list of free memory blocks and uses the first block that is big
/// enough. The runtime is in O(n) where n is the number of free blocks, but it should be
/// reasonably fast for small allocations.
pub fn allocate_first_fit(&mut self, mut size: usize, align: usize) -> Option<*mut u8> {
if size < HoleList::min_size() {
size = HoleList::min_size();
}
self.holes.allocate_first_fit(size, align)
}
/// Frees the given allocation. `ptr` must be a pointer returned
/// by a call to the `allocate_first_fit` function with identical size and alignment. Undefined
/// behavior may occur for invalid arguments, thus this function is unsafe.
///
/// This function walks the list of free memory blocks and inserts the freed block at the
/// correct place. If the freed block is adjacent to another free block, the blocks are merged
/// again. This operation is in `O(n)` since the list needs to be sorted by address.
pub unsafe fn deallocate(&mut self, ptr: *mut u8, mut size: usize, _align: usize) {
if size < HoleList::min_size() {
size = HoleList::min_size();
}
self.holes.deallocate(ptr, size);
}
/// Returns the bottom address of the heap.
pub fn bottom(&self) -> usize {
self.bottom
}
/// Returns the top address of the heap.
pub fn top(&self) -> usize {
self.top
}
}
/// Align downwards. Returns the greatest x with alignment `align` so that x<=value.
fn align_down(value: usize, align: usize) -> usize {
value / align * align
}
/// Align upwards. Returns the smallest x with alignment `align` so that value<=x.
fn align_up(value: usize, align: usize) -> usize {
align_down(value + align - 1, align)
}