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#![no_std]
#![allow(non_camel_case_types)]

use core::ffi::c_void;
use libc::size_t;

extern "C" {
    /// Allocate the memory with the given alignment and size. 
    /// On success, it returns a pointer pointing to the required memory address. 
    /// On failure, it returns a null pointer.
    /// The client must assure the following things:
    /// - `alignment` is greater than zero
    /// - `alignment` is a power of 2
    /// The program may be forced to abort if the constrains are not full-filled.
    pub fn rust_alloc(alignment: size_t, size: size_t) -> *mut c_void;

    /// De-allocate the memory at the given address with the given alignment and size. 
    /// The client must assure the following things:
    /// - the memory is acquired using the same allocator and the pointer points to the start position.
    /// - `alignment` and `size` is the same as allocation
    /// The program may be forced to abort if the constrains are not full-filled.
    pub fn rust_dealloc(ptr: *mut c_void, alignment: size_t, size: size_t) -> c_void;

    /// Re-allocate the memory at the given address with the given alignment and size. 
    /// On success, it returns a pointer pointing to the required memory address. 
    /// The memory content within the `new_size` will remains the same as previous.
    /// On failure, it returns a null pointer. In this situation, the previous memory is not returned to the allocator.
    /// The client must assure the following things:
    /// - the memory is acquired using the same allocator and the pointer points to the start position
    /// - `alignment` and `old_size` is the same as allocation
    /// - `alignment` fulfills all the requirements as `rust_alloc`
    /// The program may be forced to abort if the constrains are not full-filled.
    pub fn rust_realloc(ptr: *mut c_void, alignment: size_t, old_size: size_t, new_size: size_t) -> *mut c_void;
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_frees_memory_malloc() {
        let ptr = unsafe { rust_alloc(8, 8) } as *mut u8;
        unsafe {*ptr = 127; assert_eq!(*ptr, 127)};
        unsafe { rust_dealloc(ptr as *mut c_void, 8, 8) };
    }

    #[test]
    fn it_reallocs_correctly() {
        let mut ptr = unsafe { rust_alloc(8, 8) } as *mut u8;
        unsafe {*ptr = 127; assert_eq!(*ptr, 127)};
        ptr = unsafe { rust_realloc(ptr as *mut c_void, 8, 8, 16) } as *mut u8;
        unsafe {assert_eq!(*ptr, 127)};
        unsafe { rust_dealloc(ptr as *mut c_void, 8, 16) };
    }
}