/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Selecting the default global allocator for Servo

#[global_allocator]
static ALLOC: Allocator = Allocator;

#[cfg(not(windows))]
pub use jemalloc_sys;

pub use crate::platform::*;

#[cfg(not(windows))]
mod platform {
    use std::alloc::{GlobalAlloc, Layout};
    use std::os::raw::{c_int, c_void};

    use jemalloc_sys as ffi;

    /// Get the size of a heap block.
    pub unsafe extern "C" fn usable_size(ptr: *const c_void) -> usize {
        ffi::malloc_usable_size(ptr as *const _)
    }

    /// Memory allocation APIs compatible with libc
    pub mod libc_compat {
        pub use super::ffi::{free, malloc, realloc};
    }

    pub struct Allocator;

    // The minimum alignment guaranteed by the architecture. This value is used to
    // add fast paths for low alignment values.
    #[cfg(all(any(
        target_arch = "arm",
        target_arch = "mips",
        target_arch = "mipsel",
        target_arch = "powerpc"
    )))]
    const MIN_ALIGN: usize = 8;
    #[cfg(all(any(
        target_arch = "x86",
        target_arch = "x86_64",
        target_arch = "aarch64",
        target_arch = "powerpc64",
        target_arch = "powerpc64le",
        target_arch = "mips64",
        target_arch = "s390x",
        target_arch = "sparc64"
    )))]
    const MIN_ALIGN: usize = 16;

    fn layout_to_flags(align: usize, size: usize) -> c_int {
        // If our alignment is less than the minimum alignment they we may not
        // have to pass special flags asking for a higher alignment. If the
        // alignment is greater than the size, however, then this hits a sort of odd
        // case where we still need to ask for a custom alignment. See #25 for more
        // info.
        if align <= MIN_ALIGN && align <= size {
            0
        } else {
            // Equivalent to the MALLOCX_ALIGN(a) macro.
            align.trailing_zeros() as _
        }
    }

    unsafe impl GlobalAlloc for Allocator {
        #[inline]
        unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
            let flags = layout_to_flags(layout.align(), layout.size());
            ffi::mallocx(layout.size(), flags) as *mut u8
        }

        #[inline]
        unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
            if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
                ffi::calloc(1, layout.size()) as *mut u8
            } else {
                let flags = layout_to_flags(layout.align(), layout.size()) | ffi::MALLOCX_ZERO;
                ffi::mallocx(layout.size(), flags) as *mut u8
            }
        }

        #[inline]
        unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
            let flags = layout_to_flags(layout.align(), layout.size());
            ffi::sdallocx(ptr as *mut _, layout.size(), flags)
        }

        #[inline]
        unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
            let flags = layout_to_flags(layout.align(), new_size);
            ffi::rallocx(ptr as *mut _, new_size, flags) as *mut u8
        }
    }
}

#[cfg(windows)]
mod platform {
    pub use std::alloc::System as Allocator;
    use std::os::raw::c_void;

    use winapi::um::heapapi::{GetProcessHeap, HeapSize, HeapValidate};

    /// Get the size of a heap block.
    pub unsafe extern "C" fn usable_size(mut ptr: *const c_void) -> usize {
        let heap = GetProcessHeap();

        if HeapValidate(heap, 0, ptr) == 0 {
            ptr = *(ptr as *const *const c_void).offset(-1);
        }

        HeapSize(heap, 0, ptr) as usize
    }
}