1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
//! Fast, SIMD-accelerated CRC32 (IEEE) checksum computation.
//!
//! ## Usage
//!
//! ### Simple usage
//!
//! For simple use-cases, you can call the [`hash()`] convenience function to
//! directly compute the CRC32 checksum for a given byte slice:
//!
//! ```rust
//! let checksum = crc32fast::hash(b"foo bar baz");
//! ```
//!
//! ### Advanced usage
//!
//! For use-cases that require more flexibility or performance, for example when
//! processing large amounts of data, you can create and manipulate a [`Hasher`]:
//!
//! ```rust
//! use crc32fast::Hasher;
//!
//! let mut hasher = Hasher::new();
//! hasher.update(b"foo bar baz");
//! let checksum = hasher.finalize();
//! ```
//!
//! ## Performance
//!
//! This crate contains multiple CRC32 implementations:
//!
//! - A fast baseline implementation which processes up to 16 bytes per iteration
//! - An optimized implementation for modern `x86` using `sse` and `pclmulqdq` instructions
//!
//! Calling the [`Hasher::new`] constructor at runtime will perform a feature detection to select the most
//! optimal implementation for the current CPU feature set.

#![cfg_attr(not(feature = "std"), no_std)]
#![cfg_attr(
    all(feature = "nightly", target_arch = "aarch64"),
    feature(stdarch_arm_crc32)
)]

#[deny(missing_docs)]
#[cfg(test)]
#[macro_use]
extern crate quickcheck;

#[macro_use]
extern crate cfg_if;

#[cfg(feature = "std")]
use std as core;

use core::fmt;
use core::hash;

mod baseline;
mod combine;
mod specialized;
mod table;

/// Computes the CRC32 hash of a byte slice.
///
/// Check out [`Hasher`] for more advanced use-cases.
pub fn hash(buf: &[u8]) -> u32 {
    let mut h = Hasher::new();
    h.update(buf);
    h.finalize()
}

#[derive(Clone)]
enum State {
    Baseline(baseline::State),
    Specialized(specialized::State),
}

#[derive(Clone)]
/// Represents an in-progress CRC32 computation.
pub struct Hasher {
    amount: u64,
    state: State,
}

const DEFAULT_INIT_STATE: u32 = 0;

impl Hasher {
    /// Create a new `Hasher`.
    ///
    /// This will perform a CPU feature detection at runtime to select the most
    /// optimal implementation for the current processor architecture.
    pub fn new() -> Self {
        Self::new_with_initial(DEFAULT_INIT_STATE)
    }

    /// Create a new `Hasher` with an initial CRC32 state.
    ///
    /// This works just like `Hasher::new`, except that it allows for an initial
    /// CRC32 state to be passed in.
    pub fn new_with_initial(init: u32) -> Self {
        Self::new_with_initial_len(init, 0)
    }

    /// Create a new `Hasher` with an initial CRC32 state.
    ///
    /// As `new_with_initial`, but also accepts a length (in bytes). The
    /// resulting object can then be used with `combine` to compute `crc(a ||
    /// b)` from `crc(a)`, `crc(b)`, and `len(b)`.
    pub fn new_with_initial_len(init: u32, amount: u64) -> Self {
        Self::internal_new_specialized(init, amount)
            .unwrap_or_else(|| Self::internal_new_baseline(init, amount))
    }

    #[doc(hidden)]
    // Internal-only API. Don't use.
    pub fn internal_new_baseline(init: u32, amount: u64) -> Self {
        Hasher {
            amount,
            state: State::Baseline(baseline::State::new(init)),
        }
    }

    #[doc(hidden)]
    // Internal-only API. Don't use.
    pub fn internal_new_specialized(init: u32, amount: u64) -> Option<Self> {
        {
            if let Some(state) = specialized::State::new(init) {
                return Some(Hasher {
                    amount,
                    state: State::Specialized(state),
                });
            }
        }
        None
    }

    /// Process the given byte slice and update the hash state.
    pub fn update(&mut self, buf: &[u8]) {
        self.amount += buf.len() as u64;
        match self.state {
            State::Baseline(ref mut state) => state.update(buf),
            State::Specialized(ref mut state) => state.update(buf),
        }
    }

    /// Finalize the hash state and return the computed CRC32 value.
    pub fn finalize(self) -> u32 {
        match self.state {
            State::Baseline(state) => state.finalize(),
            State::Specialized(state) => state.finalize(),
        }
    }

    /// Reset the hash state.
    pub fn reset(&mut self) {
        self.amount = 0;
        match self.state {
            State::Baseline(ref mut state) => state.reset(),
            State::Specialized(ref mut state) => state.reset(),
        }
    }

    /// Combine the hash state with the hash state for the subsequent block of bytes.
    pub fn combine(&mut self, other: &Self) {
        self.amount += other.amount;
        let other_crc = other.clone().finalize();
        match self.state {
            State::Baseline(ref mut state) => state.combine(other_crc, other.amount),
            State::Specialized(ref mut state) => state.combine(other_crc, other.amount),
        }
    }
}

impl fmt::Debug for Hasher {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("crc32fast::Hasher").finish()
    }
}

impl Default for Hasher {
    fn default() -> Self {
        Self::new()
    }
}

impl hash::Hasher for Hasher {
    fn write(&mut self, bytes: &[u8]) {
        self.update(bytes)
    }

    fn finish(&self) -> u64 {
        u64::from(self.clone().finalize())
    }
}

#[cfg(test)]
mod test {
    use super::Hasher;

    quickcheck! {
        fn combine(bytes_1: Vec<u8>, bytes_2: Vec<u8>) -> bool {
            let mut hash_a = Hasher::new();
            hash_a.update(&bytes_1);
            hash_a.update(&bytes_2);
            let mut hash_b = Hasher::new();
            hash_b.update(&bytes_2);
            let mut hash_c = Hasher::new();
            hash_c.update(&bytes_1);
            hash_c.combine(&hash_b);

            hash_a.finalize() == hash_c.finalize()
        }

        fn combine_from_len(bytes_1: Vec<u8>, bytes_2: Vec<u8>) -> bool {
            let mut hash_a = Hasher::new();
            hash_a.update(&bytes_1);
            let a = hash_a.finalize();

            let mut hash_b = Hasher::new();
            hash_b.update(&bytes_2);
            let b = hash_b.finalize();

            let mut hash_ab = Hasher::new();
            hash_ab.update(&bytes_1);
            hash_ab.update(&bytes_2);
            let ab = hash_ab.finalize();

            let mut reconstructed = Hasher::new_with_initial_len(a, bytes_1.len() as u64);
            let hash_b_reconstructed = Hasher::new_with_initial_len(b, bytes_2.len() as u64);

            reconstructed.combine(&hash_b_reconstructed);

            reconstructed.finalize() == ab
        }
    }
}