Whole new world

Updated to use new libdeflate integration that I implemented upstream in https://github.com/shssoichiro/oxipng/pull/203.

codecs/oxipng/src/malloc_shim.rs

@@ -0,0 +1,27 @@
+//! This is a module that provides `malloc` and `free` for `libdeflate`.
+//! These implementations are compatible with the standard signatures
+//! but use Rust allocator instead of including libc one as well.
+//!
+//! I've raised an upstream issue to hopefully make this easier in
+//! future: https://github.com/ebiggers/libdeflate/issues/62
+
+use std::alloc::*;
+use std::mem::{align_of, size_of};
+
+unsafe fn layout_for(size: usize) -> Layout {
+    Layout::from_size_align_unchecked(size_of::<usize>() + size, align_of::<usize>())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn malloc(size: usize) -> *mut u8 {
+    let size_and_data_ptr = alloc(layout_for(size));
+    *(size_and_data_ptr as *mut usize) = size;
+    size_and_data_ptr.add(size_of::<usize>())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn free(ptr: *mut u8) {
+    let size_and_data_ptr = ptr.sub(size_of::<usize>());
+    let size = *(size_and_data_ptr as *const usize);
+    dealloc(ptr, layout_for(size))
+}