# smallnum
Integer optimization: macros return the smallest integer type capable of fitting a static bounds.
Both signed (e.g. macro input is maximum) and unsigned (e.g. macro input is maximum or minimum) numbers supported.
Saves memory on embedded devices.
`!#[no_std]`, `#![forbid(unsafe_code)]`, zero-cost.
### Example: Statically-sized Collection Index
When the size of a collection is known at compile-time, the variable used to index it can be size-optimized.
```rust
use smallnum::{small_unsigned, SmallUnsigned};
use core::mem::size_of_val;
const MAX_CAPACITY: usize = 500;
let my_array: [u8; MAX_CAPACITY] = [0; MAX_CAPACITY];
let idx: usize = 5;
let small_idx: small_unsigned!(MAX_CAPACITY) = 5;
assert_eq!(idx, small_idx.usize()); // Equivalent values
assert_eq!(my_array[idx], my_array[small_idx.usize()]); // Equivalent collection indexing
assert!(size_of_val(&idx) > size_of_val(&small_idx)); // Memory savings (6 bytes on 64-bit)
#[cfg(target_pointer_width = "64")]
assert_eq!(size_of_val(&idx), 8);
#[cfg(target_pointer_width = "64")]
assert_eq!(size_of_val(&small_idx), 2);
```
### Example: Tree Node Metadata
When the maximum capacity of a tree is known at compile-time, metadata stored in every node can be size-optimized.
```rust
use smallnum::small_unsigned;
use core::mem::size_of;
const MAX_CAPACITY: usize = 500;
// Regular node in a binary tree
struct BinTree<T> {
value: T,
left_child: Option<Box<BinTree<T>>>,
right_child: Option<Box<BinTree<T>>>,
subtree_size: Option<usize>,
}
// Node with size-optimized metadata
struct SmallBinTree<T> {
value: T,
left_child: Option<Box<SmallBinTree<T>>>,
right_child: Option<Box<SmallBinTree<T>>>,
subtree_size: Option<small_unsigned!(MAX_CAPACITY)>,
}
// Per-node memory savings (16 bytes on 64-bit)
assert!(size_of::<BinTree<u8>>() > size_of::<SmallBinTree<u8>>());
#[cfg(target_pointer_width = "64")]
assert_eq!(size_of::<BinTree<u8>>(), 40);
#[cfg(target_pointer_width = "64")]
assert_eq!(size_of::<SmallBinTree<u8>>(), 24);
```