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//! A simple slab allocator for pages in wasm
#![cfg(target_arch = "wasm32")]
use std::ptr;
use core_arch::arch::wasm32::*;
static mut HEAD: *mut *mut u8 = 0 as _;
#[unsafe(no_mangle)]
pub unsafe extern "C" fn page_alloc() -> *mut u8 {
unsafe {
if !HEAD.is_null() {
let next = *HEAD;
let ret = HEAD;
HEAD = next as *mut _;
return ret as *mut u8;
}
}
let ret = memory_grow(0, 1);
// if we failed to allocate a page then return null
if ret == usize::MAX {
return ptr::null_mut();
}
((ret as u32) * page_size()) as *mut u8
}
#[unsafe(no_mangle)]
pub unsafe extern "C" fn page_free(page: *mut u8) {
let page = page as *mut *mut u8;
unsafe {
*page = HEAD as *mut u8;
HEAD = page;
}
}
#[unsafe(no_mangle)]
pub unsafe extern "C" fn memory_used() -> usize {
(page_size() * (memory_size(0) as u32)) as usize
}
fn page_size() -> u32 {
64 * 1024
}
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