# smallmap
A small table map using single byte key indecies. Designed for maps with tiny keys.
Pages are stored as 256 entry key-value arrays which are indexed by the byte key index. The key is compared for collision check and on collision the next page is checked or inserted if needed.
`smallmap` does not ever need to allocate more than 1 page for types which all invariants can be represented as unique bytes.
## Usage
The API is a similar subset to `HashMap` , containing the same `insert` , `get` , and `entry` functions:
``` rust
fn max_char(chars: & str) -> (char, usize)
{
let mut map = Map::new();
for x in chars.chars() {
*map.entry(x).or_insert(0usize) += 1;
}
map.into_iter().max_by_key(|& (_, v)| v).unwrap_or_default()
}
```
## Use cases
Designed for instances where you want a small map with relatively trivial keys (e.g. primitive type).
Performance can greately outpace hash-based by an order of magnitude or more in these cases.
### Maybe use if
* You have small keys
* Your map is not at risk of Denial of Service attacks.
* Your keys will have a lot of collisions
### Don't use if
* You have complex keys
* Denial of service is a concern
* Your map will contain a large volume of entries
* Your keys may have a large number of collisions when represented as `u8` .
# Benchmarks
Some crude and basic benchmarks
## char
| Which | ns/iter |
|-----------------|---------|
| `HashMap` | 16 |
| `smallmap::Map` | 7 |
## Iterating a string's chars and counting each
| Which | ns/iter (entry) | ns/iter (get/insert) |
|-----------------|-----------------|----------------------|
| `HashMap` | 8,418 | 8,367 |
| `BTreeMap` | 9,742 | 6,329 |
| `smallmap::Map` | 4,416 | 1,739 |
## u8
| Which | ns/iter |
|-----------------|---------|
| `HashMap` | 15 |
| `smallmap::Map` | 2 |
# License
MIT licensed
