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denoland-deno/ext/node/ops/zlib/alloc.rs

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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
2023-03-27 12:03:07 -04:00
// Workaround for https://github.com/rust-lang/libz-sys/issues/55
// See https://github.com/rust-lang/flate2-rs/blob/31fb07820345691352aaa64f367c1e482ad9cfdc/src/ffi/c.rs#L60
use std::alloc::Layout;
use std::alloc::{self};
use std::os::raw::c_void;
use std::ptr;
const ALIGN: usize = std::mem::align_of::<usize>();
fn align_up(size: usize, align: usize) -> usize {
(size + align - 1) & !(align - 1)
}
pub extern "C" fn zalloc(
_ptr: *mut c_void,
items: u32,
item_size: u32,
) -> *mut c_void {
// We need to multiply `items` and `item_size` to get the actual desired
// allocation size. Since `zfree` doesn't receive a size argument we
// also need to allocate space for a `usize` as a header so we can store
// how large the allocation is to deallocate later.
let size = match (items as usize)
.checked_mul(item_size as usize)
.map(|size| align_up(size, ALIGN))
.and_then(|i| i.checked_add(std::mem::size_of::<usize>()))
{
Some(i) => i,
None => return ptr::null_mut(),
};
// Make sure the `size` isn't too big to fail `Layout`'s restrictions
let layout = match Layout::from_size_align(size, ALIGN) {
Ok(layout) => layout,
Err(_) => return ptr::null_mut(),
};
// SAFETY: `layout` has non-zero size, guaranteed to be a sentinel address
// or a null pointer.
unsafe {
// Allocate the data, and if successful store the size we allocated
// at the beginning and then return an offset pointer.
let ptr = alloc::alloc(layout) as *mut usize;
if ptr.is_null() {
return ptr as *mut c_void;
}
*ptr = size;
ptr.add(1) as *mut c_void
}
}
pub extern "C" fn zfree(_ptr: *mut c_void, address: *mut c_void) {
// SAFETY: Move our address being free'd back one pointer, read the size we
// stored in `zalloc`, and then free it using the standard Rust
// allocator.
unsafe {
let ptr = (address as *mut usize).offset(-1);
let size = *ptr;
let layout = Layout::from_size_align_unchecked(size, ALIGN);
alloc::dealloc(ptr as *mut u8, layout)
}
}