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// Copyright 2019 Octavian Oncescu

#![no_std]

//! A drop-in global allocator wrapper around the [mimalloc](https://github.com/microsoft/mimalloc) allocator.
//! Mimalloc is a general purpose, performance oriented allocator built by Microsoft.
//!
//! ## Usage
//! ```rust,ignore
//! use mimalloc::MiMalloc;
//!
//! #[global_allocator]
//! static GLOBAL: MiMalloc = MiMalloc;
//! ```
//!
//! ## Usage without secure mode
//! By default this library builds mimalloc in secure mode. This means that
//! heap allocations are encrypted, but this results in a 3% increase in overhead.
//!
//! To disable secure mode, in `Cargo.toml`:
//! ```rust,ignore
//! [dependencies]
//! mimalloc = { version = "*", default-features = false }
//! ```

extern crate libmimalloc_sys as ffi;

use core::alloc::{GlobalAlloc, Layout};
use ffi::*;
use core::ffi::c_void;

// Copied from https://github.com/rust-lang/rust/blob/master/src/libstd/sys_common/alloc.rs
#[cfg(all(any(
    target_arch = "x86",
    target_arch = "arm",
    target_arch = "mips",
    target_arch = "powerpc",
    target_arch = "powerpc64",
    target_arch = "asmjs",
    target_arch = "wasm32"
)))]
const MIN_ALIGN: usize = 8;

#[cfg(all(any(
    target_arch = "x86_64",
    target_arch = "aarch64",
    target_arch = "mips64",
    target_arch = "s390x",
    target_arch = "sparc64"
)))]
const MIN_ALIGN: usize = 16;

/// Drop-in mimalloc global allocator.
///
/// ## Usage
/// ```rust,ignore
/// use mimalloc::MiMalloc;
///
/// #[global_allocator]
/// static GLOBAL: MiMalloc = MiMalloc;
/// ```
pub struct MiMalloc;

unsafe impl GlobalAlloc for MiMalloc {
    #[inline]
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
            mi_malloc(layout.size()) as *mut u8
        } else {
            if cfg!(target_os = "macos") {
                if layout.align() > (1 << 31) {
                    return core::ptr::null_mut();
                }
            }

            mi_malloc_aligned(layout.size(), layout.align()) as *mut u8
        }
    }

    #[inline]
    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
            mi_zalloc(layout.size()) as *mut u8
        } else {
            if cfg!(target_os = "macos") {
                if layout.align() > (1 << 31) {
                    return core::ptr::null_mut();
                }
            }

            mi_zalloc_aligned(layout.size(), layout.align()) as *mut u8
        }
    }

    #[inline]
    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
        mi_free(ptr as *mut c_void);
    }

    #[inline]
    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
            mi_realloc(ptr as *mut c_void, new_size) as *mut u8
        } else {
            mi_realloc_aligned(ptr as *mut c_void, new_size, layout.align()) as *mut u8
        }
    }
}

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

    #[test]
    fn it_frees_allocated_memory() {
        unsafe {
            let layout = Layout::from_size_align(8, 8).unwrap();
            let alloc = MiMalloc;

            let ptr = alloc.alloc(layout.clone());
            alloc.dealloc(ptr, layout);
        }
    }

    #[test]
    fn it_frees_zero_allocated_memory() {
        unsafe {
            let layout = Layout::from_size_align(8, 8).unwrap();
            let alloc = MiMalloc;

            let ptr = alloc.alloc_zeroed(layout.clone());
            alloc.dealloc(ptr, layout);
        }
    }

    #[test]
    fn it_frees_reallocated_memory() {
        unsafe {
            let layout = Layout::from_size_align(8, 8).unwrap();
            let alloc = MiMalloc;

            let ptr = alloc.alloc(layout.clone());
            let ptr = alloc.realloc(ptr, layout.clone(), 16);
            alloc.dealloc(ptr, layout);
        }
    }
}