chopalloc

A minimal, no_std buddy allocator for embedded systems and bare-metal environments.

Features

• bitmap (default): Enables O(1) buddy checking using a bitmap. Disable for pure free-list implementation (O(n) checks, less memory overhead).

Choosing MAX_ORDER

The MAX_ORDER const generic parameter determines how many block size levels the allocator manages.

Formula: MAX_ORDER = log2(memory_size_in_bytes) + 1

Examples:

• 1 KB (1024 bytes) → BuddyAllocator::<11> (2^10 = 1024)
• 4 KB (4096 bytes) → BuddyAllocator::<13> (2^12 = 4096)
• 64 KB (65536 bytes) → BuddyAllocator::<17> (2^16 = 65536)

The allocator will manage blocks from 2^0 up to 2^(MAX_ORDER-1) bytes.

Usage

use chopalloc::BuddyAllocator;
use core::alloc::Layout;

// With bitmap (default)
#[repr(align(1024))]
static mut MEMORY: [u8; 1024] = [0; 1024];
static mut BITMAP: [u64; 64] = [0; 64];

let allocator = unsafe {
    let memory_ptr = NonNull::new(MEMORY.as_mut_ptr()).unwrap();
    let bitmap_words = BuddyAllocator::<11>::calculate_bitmap_words_needed(1024);
    let bitmap_slice = &mut BITMAP[..bitmap_words];
    BuddyAllocator::<11>::new(memory_ptr, 1024, bitmap_slice).unwrap()
};

let layout = Layout::from_size_align(64, 64).unwrap();
let ptr = allocator.try_allocate(layout).unwrap();
allocator.try_deallocate(ptr, layout).unwrap();

Without Bitmap

// In Cargo.toml: chopalloc = { version = "1.0", default-features = false }

let allocator = unsafe {
    let memory_ptr = NonNull::new(MEMORY.as_mut_ptr()).unwrap();
    BuddyAllocator::<11>::new(memory_ptr, 1024).unwrap() // No bitmap parameter
};

Alignment Requirements

The backing memory region must be aligned to the allocator's largest block size (BuddyAllocator::largest_block_size()). Use #[repr(align(...))] for static buffers:

#[repr(align(1024))]  // Align to largest block size
static mut MEMORY: [u8; 1024] = [0; 1024];

Examples

See examples/ for:

• basic_usage.rs - Fundamental operations
• fragmentation_demo.rs - Buddy merging behavior
• embedded_simulation.rs - Simulated embedded system
• no_bitmap.rs - Free-list-only mode (compile with --no-default-features)