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use std::mem;
pub const EMPTY: *mut () = 0x1 as *mut ();
#[inline]
pub unsafe fn allocate(size: usize, align: usize) -> *mut u8 {
assert!(size & align == 0, "invalid allocate arguments; size={}; align={}", size, align);
match align {
1 => do_allocate::<u8>(size),
2 => do_allocate::<u16>(size >> 1),
4 => do_allocate::<u32>(size >> 2),
8 => do_allocate::<u64>(size >> 3),
_ => panic!("unsupported alignment {}", align),
}
}
unsafe fn do_allocate<T>(capacity: usize) -> *mut u8 {
let vec = Vec::<T>::with_capacity(capacity);
let ptr = vec.as_ptr();
mem::forget(vec);
ptr as *mut u8
}
#[inline]
pub unsafe fn deallocate(ptr: *mut u8, old_size: usize, align: usize) {
match align {
1 => do_deallocate::<u8>(ptr, old_size),
2 => do_deallocate::<u16>(ptr, old_size >> 1),
4 => do_deallocate::<u32>(ptr, old_size >> 2),
8 => do_deallocate::<u64>(ptr, old_size >> 3),
_ => panic!("unsupported alignment {}", align),
}
}
unsafe fn do_deallocate<T>(ptr: *mut u8, capacity: usize) {
let _ = Vec::from_raw_parts(ptr as *mut T, 0, capacity);
}
#[cfg(test)]
mod test {
use std::mem;
#[test]
fn test_align() {
assert_eq!(1, mem::align_of::<u8>());
assert_eq!(2, mem::align_of::<u16>());
assert_eq!(4, mem::align_of::<u32>());
assert_eq!(8, mem::align_of::<u64>());
}
#[test]
fn test_allocate_deallocate() {
unsafe {
::deallocate(::allocate(2048, 4), 2048, 4);
}
}
#[test]
fn test_empty_constant() {
let mut v = Vec::<()>::with_capacity(0);
assert_eq!(::EMPTY, v.as_mut_ptr());
}
}