arrow 10.0.0

Rust implementation of Apache Arrow
Documentation 
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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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.

//! Defines memory-related functions, such as allocate/deallocate/reallocate memory
//! regions, cache and allocation alignments.

use std::alloc::{handle_alloc_error, Layout};
use std::mem::size_of;
use std::ptr::NonNull;

mod alignment;
mod types;

pub use alignment::ALIGNMENT;
pub use types::NativeType;

#[inline]
unsafe fn null_pointer<T: NativeType>() -> NonNull<T> {
    NonNull::new_unchecked(ALIGNMENT as *mut T)
}

/// Allocates a cache-aligned memory region of `size` bytes with uninitialized values.
/// This is more performant than using [allocate_aligned_zeroed] when all bytes will have
/// an unknown or non-zero value and is semantically similar to `malloc`.
pub fn allocate_aligned<T: NativeType>(size: usize) -> NonNull<T> {
    unsafe {
        if size == 0 {
            null_pointer()
        } else {
            let size = size * size_of::<T>();

            let layout = Layout::from_size_align_unchecked(size, ALIGNMENT);
            let raw_ptr = std::alloc::alloc(layout) as *mut T;
            NonNull::new(raw_ptr).unwrap_or_else(|| handle_alloc_error(layout))
        }
    }
}

/// Allocates a cache-aligned memory region of `size` bytes with `0` on all of them.
/// This is more performant than using [allocate_aligned] and setting all bytes to zero
/// and is semantically similar to `calloc`.
pub fn allocate_aligned_zeroed<T: NativeType>(size: usize) -> NonNull<T> {
    unsafe {
        if size == 0 {
            null_pointer()
        } else {
            let size = size * size_of::<T>();

            let layout = Layout::from_size_align_unchecked(size, ALIGNMENT);
            let raw_ptr = std::alloc::alloc_zeroed(layout) as *mut T;
            NonNull::new(raw_ptr).unwrap_or_else(|| handle_alloc_error(layout))
        }
    }
}

/// # Safety
///
/// This function is unsafe because undefined behavior can result if the caller does not ensure all
/// of the following:
///
/// * ptr must denote a block of memory currently allocated via this allocator,
///
/// * size must be the same size that was used to allocate that block of memory,
pub unsafe fn free_aligned<T: NativeType>(ptr: NonNull<T>, size: usize) {
    if ptr != null_pointer() {
        let size = size * size_of::<T>();
        std::alloc::dealloc(
            ptr.as_ptr() as *mut u8,
            Layout::from_size_align_unchecked(size, ALIGNMENT),
        );
    }
}

/// # Safety
///
/// This function is unsafe because undefined behavior can result if the caller does not ensure all
/// of the following:
///
/// * ptr must be currently allocated via this allocator,
///
/// * new_size must be greater than zero.
///
/// * new_size, when rounded up to the nearest multiple of [ALIGNMENT], must not overflow (i.e.,
/// the rounded value must be less than usize::MAX).
pub unsafe fn reallocate<T: NativeType>(
    ptr: NonNull<T>,
    old_size: usize,
    new_size: usize,
) -> NonNull<T> {
    let old_size = old_size * size_of::<T>();
    let new_size = new_size * size_of::<T>();
    if ptr == null_pointer() {
        return allocate_aligned(new_size);
    }

    if new_size == 0 {
        free_aligned(ptr, old_size);
        return null_pointer();
    }

    let raw_ptr = std::alloc::realloc(
        ptr.as_ptr() as *mut u8,
        Layout::from_size_align_unchecked(old_size, ALIGNMENT),
        new_size,
    ) as *mut T;
    NonNull::new(raw_ptr).unwrap_or_else(|| {
        handle_alloc_error(Layout::from_size_align_unchecked(new_size, ALIGNMENT))
    })
}