ramp 0.7.0

A high-performance multiple-precision arithmetic library
Documentation 
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// Copyright 2015 The Ramp Developers
//
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
//
//        http://www.apache.org/licenses/LICENSE-2.0
//
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.

//! Memory management functions. The base functions align to a pointer-width, so they shouldn't
//! be used for anything that requires an alignment greater than that.

use std::alloc;
use std::intrinsics::abort;
use std::io::{self, Write};
use std::mem;
use std::ptr;

use ll::limb::Limb;
use ll::limb_ptr::LimbsMut;

/// Returns a Layout with the given size and pointer-width (i.e., usize) alignment. Panics if
/// unable to create the Layout.
unsafe fn get_usize_align_layout(size: usize) -> alloc::Layout {
    let alignment = mem::align_of::<usize>();

    match alloc::Layout::from_size_align(size, alignment) {
        Ok(l) => l,
        Err(layout_err) => {
            let _ = writeln!(
                io::stderr(),
                "Failed to construct mem layout (size={}, alignment={}): {}",
                size,
                alignment,
                layout_err
            );
            abort();
        }
    }
}

pub unsafe fn allocate_bytes(size: usize) -> *mut u8 {
    let layout = get_usize_align_layout(size);
    let ret = alloc::alloc_zeroed(layout.clone());
    if ret.is_null() {
        writeln!(
            io::stderr(),
            "Failed to allocate memory (layout={:?})",
            layout,
        )
        .unwrap();
        abort();
    };

    ptr::write_bytes(ret, 0, size);
    ret
}

pub unsafe fn deallocate_bytes(ptr: ptr::NonNull<u8>, size: usize) {
    let layout = get_usize_align_layout(size);
    alloc::dealloc(ptr.as_ptr(), layout);
}

/// Allocate for temporary storage. Ensures that the allocations are
/// freed when the structure drops
pub struct TmpAllocator {
    mark: *mut Marker,
}

struct Marker {
    next: *mut Marker,
    size: usize,
}

impl TmpAllocator {
    pub fn new() -> TmpAllocator {
        TmpAllocator {
            mark: ptr::null_mut(),
        }
    }

    pub unsafe fn allocate_bytes(&mut self, size: usize) -> *mut u8 {
        let size = size + mem::size_of::<Marker>();
        let ptr = allocate_bytes(size);

        let mark = ptr as *mut Marker;
        (*mark).size = size;
        (*mark).next = self.mark;

        self.mark = mark;

        ptr.offset(mem::size_of::<Marker>() as isize)
    }

    /// Allocate space for n limbs
    pub unsafe fn allocate(&mut self, n: usize) -> LimbsMut {
        let ptr = self.allocate_bytes(n * mem::size_of::<Limb>()) as *mut Limb;
        LimbsMut::new(ptr, 0, n as i32)
    }

    /// Allocates space for n1+n2 limbs and returns a pair of pointers.
    pub unsafe fn allocate_2(&mut self, n1: usize, n2: usize) -> (LimbsMut, LimbsMut) {
        let mut x = self.allocate(n1 + n2);
        let mut y = x.offset(n1 as isize);
        (
            LimbsMut::new(&mut *x, 0, n1 as i32),
            LimbsMut::new(&mut *y, 0, n2 as i32),
        )
    }
}

impl Drop for TmpAllocator {
    fn drop(&mut self) {
        unsafe {
            let mut next;
            let mut mark = self.mark;
            // Iterate the list until we hit a null ptr
            while let Some(checked_mark) = ptr::NonNull::new(mark) {
                next = checked_mark.as_ref().next;
                let size = checked_mark.as_ref().size;
                deallocate_bytes(checked_mark.cast(), size);
                mark = next;
            }
        }
    }
}