Revision control
Copy as Markdown
Other Tools
//! Adler-32 checksum implementation.
//!
//! This implementation features:
//!
//! - Permissively licensed (0BSD) clean-room implementation.
//! - Zero dependencies.
//! - Zero `unsafe`.
//! - Decent performance (3-4 GB/s).
//! - `#![no_std]` support (with `default-features = false`).
// Deny a few warnings in doctests, since rustdoc `allow`s many warnings by default
#![doc(test(attr(deny(unused_imports, unused_must_use))))]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![warn(missing_debug_implementations)]
#![forbid(unsafe_code)]
#![cfg_attr(not(feature = "std"), no_std)]
#[cfg(not(feature = "std"))]
extern crate core as std;
mod algo;
use std::hash::Hasher;
#[cfg(feature = "std")]
use std::io::{self, BufRead};
/// Adler-32 checksum calculator.
///
/// An instance of this type is equivalent to an Adler-32 checksum: It can be created in the default
/// state via [`new`] (or the provided `Default` impl), or from a precalculated checksum via
/// [`from_checksum`], and the currently stored checksum can be fetched via [`checksum`].
///
/// This type also implements `Hasher`, which makes it easy to calculate Adler-32 checksums of any
/// type that implements or derives `Hash`. This also allows using Adler-32 in a `HashMap`, although
/// that is not recommended (while every checksum is a hash function, they are not necessarily a
/// good one).
///
/// # Examples
///
/// Basic, piecewise checksum calculation:
///
/// ```
/// use adler::Adler32;
///
/// let mut adler = Adler32::new();
///
/// adler.write_slice(&[0, 1, 2]);
/// adler.write_slice(&[3, 4, 5]);
///
/// assert_eq!(adler.checksum(), 0x00290010);
/// ```
///
/// Using `Hash` to process structures:
///
/// ```
/// use std::hash::Hash;
/// use adler::Adler32;
///
/// #[derive(Hash)]
/// struct Data {
/// byte: u8,
/// word: u16,
/// big: u64,
/// }
///
/// let mut adler = Adler32::new();
///
/// let data = Data { byte: 0x1F, word: 0xABCD, big: !0 };
/// data.hash(&mut adler);
///
/// // hash value depends on architecture endianness
/// if cfg!(target_endian = "little") {
/// assert_eq!(adler.checksum(), 0x33410990);
/// }
/// if cfg!(target_endian = "big") {
/// assert_eq!(adler.checksum(), 0x331F0990);
/// }
///
/// ```
///
/// [`new`]: #method.new
/// [`from_checksum`]: #method.from_checksum
/// [`checksum`]: #method.checksum
#[derive(Debug, Copy, Clone)]
pub struct Adler32 {
a: u16,
b: u16,
}
impl Adler32 {
/// Creates a new Adler-32 instance with default state.
#[inline]
pub fn new() -> Self {
Self::default()
}
/// Creates an `Adler32` instance from a precomputed Adler-32 checksum.
///
/// This allows resuming checksum calculation without having to keep the `Adler32` instance
/// around.
///
/// # Example
///
/// ```
/// # use adler::Adler32;
/// let parts = [
/// "rust",
/// "acean",
/// ];
/// let whole = adler::adler32_slice(b"rustacean");
///
/// let mut sum = Adler32::new();
/// sum.write_slice(parts[0].as_bytes());
/// let partial = sum.checksum();
///
/// // ...later
///
/// let mut sum = Adler32::from_checksum(partial);
/// sum.write_slice(parts[1].as_bytes());
/// assert_eq!(sum.checksum(), whole);
/// ```
#[inline]
pub fn from_checksum(sum: u32) -> Self {
Adler32 {
a: sum as u16,
b: (sum >> 16) as u16,
}
}
/// Returns the calculated checksum at this point in time.
#[inline]
pub fn checksum(&self) -> u32 {
(u32::from(self.b) << 16) | u32::from(self.a)
}
/// Adds `bytes` to the checksum calculation.
///
/// If efficiency matters, this should be called with Byte slices that contain at least a few
/// thousand Bytes.
pub fn write_slice(&mut self, bytes: &[u8]) {
self.compute(bytes);
}
}
impl Default for Adler32 {
#[inline]
fn default() -> Self {
Adler32 { a: 1, b: 0 }
}
}
impl Hasher for Adler32 {
#[inline]
fn finish(&self) -> u64 {
u64::from(self.checksum())
}
fn write(&mut self, bytes: &[u8]) {
self.write_slice(bytes);
}
}
/// Calculates the Adler-32 checksum of a byte slice.
///
/// This is a convenience function around the [`Adler32`] type.
///
/// [`Adler32`]: struct.Adler32.html
pub fn adler32_slice(data: &[u8]) -> u32 {
let mut h = Adler32::new();
h.write_slice(data);
h.checksum()
}
/// Calculates the Adler-32 checksum of a `BufRead`'s contents.
///
/// The passed `BufRead` implementor will be read until it reaches EOF (or until it reports an
/// error).
///
/// If you only have a `Read` implementor, you can wrap it in `std::io::BufReader` before calling
/// this function.
///
/// # Errors
///
/// Any error returned by the reader are bubbled up by this function.
///
/// # Examples
///
/// ```no_run
/// # fn run() -> Result<(), Box<dyn std::error::Error>> {
/// use adler::adler32;
///
/// use std::fs::File;
/// use std::io::BufReader;
///
/// let file = File::open("input.txt")?;
/// let mut file = BufReader::new(file);
///
/// adler32(&mut file)?;
/// # Ok(()) }
/// # fn main() { run().unwrap() }
/// ```
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
pub fn adler32<R: BufRead>(mut reader: R) -> io::Result<u32> {
let mut h = Adler32::new();
loop {
let len = {
let buf = reader.fill_buf()?;
if buf.is_empty() {
return Ok(h.checksum());
}
h.write_slice(buf);
buf.len()
};
reader.consume(len);
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn zeroes() {
assert_eq!(adler32_slice(&[]), 1);
assert_eq!(adler32_slice(&[0]), 1 | 1 << 16);
assert_eq!(adler32_slice(&[0, 0]), 1 | 2 << 16);
assert_eq!(adler32_slice(&[0; 100]), 0x00640001);
assert_eq!(adler32_slice(&[0; 1024]), 0x04000001);
assert_eq!(adler32_slice(&[0; 1024 * 1024]), 0x00f00001);
}
#[test]
fn ones() {
assert_eq!(adler32_slice(&[0xff; 1024]), 0x79a6fc2e);
assert_eq!(adler32_slice(&[0xff; 1024 * 1024]), 0x8e88ef11);
}
#[test]
fn mixed() {
assert_eq!(adler32_slice(&[1]), 2 | 2 << 16);
assert_eq!(adler32_slice(&[40]), 41 | 41 << 16);
assert_eq!(adler32_slice(&[0xA5; 1024 * 1024]), 0xd5009ab1);
}
#[test]
fn wiki() {
assert_eq!(adler32_slice(b"Wikipedia"), 0x11E60398);
}
#[test]
fn resume() {
let mut adler = Adler32::new();
adler.write_slice(&[0xff; 1024]);
let partial = adler.checksum();
assert_eq!(partial, 0x79a6fc2e); // from above
adler.write_slice(&[0xff; 1024 * 1024 - 1024]);
assert_eq!(adler.checksum(), 0x8e88ef11); // from above
// Make sure that we can resume computing from the partial checksum via `from_checksum`.
let mut adler = Adler32::from_checksum(partial);
adler.write_slice(&[0xff; 1024 * 1024 - 1024]);
assert_eq!(adler.checksum(), 0x8e88ef11); // from above
}
#[cfg(feature = "std")]
#[test]
fn bufread() {
use std::io::BufReader;
fn test(data: &[u8], checksum: u32) {
// `BufReader` uses an 8 KB buffer, so this will test buffer refilling.
let mut buf = BufReader::new(data);
let real_sum = adler32(&mut buf).unwrap();
assert_eq!(checksum, real_sum);
}
test(&[], 1);
test(&[0; 1024], 0x04000001);
test(&[0; 1024 * 1024], 0x00f00001);
test(&[0xA5; 1024 * 1024], 0xd5009ab1);
}
}