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+//! 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`).
+
+#![doc(html_root_url = "https://docs.rs/adler/1.0.2")]
+// 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);
+ }
+
+ /// Example calculation from https://en.wikipedia.org/wiki/Adler-32.
+ #[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);
+ }
+}
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