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// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//! RFC 1071 "internet checksum" computation.
//!
//! This crate implements the "internet checksum" defined in [RFC 1071] and
//! updated in [RFC 1141] and [RFC 1624], which is used by many different
//! protocols' packet formats. The checksum operates by computing the 1s
//! complement of the 1s complement sum of successive 16-bit words of the input.
//!
//! # Benchmarks
//!
//! ## [`Checksum::add_bytes`]
//!
//! The following microbenchmarks were performed on a 2018 Google Pixelbook. Each benchmark
//! constructs a [`Checksum`] object, calls [`Checksum::add_bytes`] with an input of the given
//! number of bytes, and then calls [`Checksum::checksum`] to finalize. Average values were
//! calculated over 3 trials.
//!
//! Bytes | Time | Rate
//! ----- | ---------- | ----------
//! 20 | 2,649 ns | 7.55 MB/s
//! 31 | 3,826 ns | 8.10 MB/s
//! 32 | 3,871 ns | 8.27 MB/s
//! 64 | 1,433 ns | 44.7 MB/s
//! 128 | 2,225 ns | 57.5 MB/s
//! 256 | 3,829 ns | 66.9 MB/s
//! 1023 | 13,802 ns | 74.1 MB/s
//! 1024 | 13,535 ns | 75.7 MB/s
//!
//! ## [`Checksum::add_bytes_small`]
//!
//! The following microbenchmarks were performed on a 2018 Google Pixelbook. Each benchmark
//! constructs a [`Checksum`] object, calls [`Checksum::add_bytes_small`] with an input of the
//! given number of bytes, and then calls [`Checksum::checksum`] to finalize. Average values
//! were calculated over 3 trials.
//!
//! Bytes | Time | Rate
//! ----- | ---------- | ----------
//! 20 | 2,639 ns | 7.57 MB/s
//! 31 | 3,806 ns | 8.15 MB/s
//!
//! ## [`update`]
//!
//! The following microbenchmarks were performed on a 2018 Google Pixelbook. Each benchmark
//! calls [`update`] with an original 2 byte checksum, and byteslices of specified lengths
//! to be updated. Average values were calculated over 3 trials.
//!
//! Bytes | Time | Rate
//! ----- | ---------- | ----------
//! 2 | 1,550 ns | 1.29 MB/s
//! 4 | 1,972 ns | 2.03 MB/s
//! 8 | 2,892 ns | 2.77 MB/s
//!
//! [RFC 1071]: https://tools.ietf.org/html/rfc1071
//! [RFC 1141]: https://tools.ietf.org/html/rfc1141
//! [RFC 1624]: https://tools.ietf.org/html/rfc1624
// Optimizations applied:
//
// 0. Byteorder independence: as described in RFC 1071 section 2.(B)
// The sum of 16-bit integers can be computed in either byte order,
// so this actually saves us from the unnecessary byte swapping on
// an LE machine. As perfed on a gLinux workstation, that swapping
// can account for ~20% of the runtime.
//
// 1. Widen the accumulator: doing so enables us to process a bigger
// chunk of data once at a time, achieving some kind of poor man's
// SIMD. Currently a u128 counter is used on x86-64 and a u64 is
// used conservatively on other architectures.
//
// 2. Process more at a time: the old implementation uses a u32 accumulator
// but it only adds one u16 each time to implement deferred carry. In
// the current implementation we are processing a u128 once at a time
// on x86-64, which is 8 u16's. On other platforms, we are processing
// a u64 at a time, which is 4 u16's.
//
// 3. Induce the compiler to produce `adc` instruction: this is a very
// useful instruction to implement 1's complement addition and available
// on both x86 and ARM. The functions `adc_uXX` are for this use.
//
// 4. Eliminate branching as much as possible: the old implementation has
// if statements for detecting overflow of the u32 accumulator which
// is not needed when we can access the carry flag with `adc`. The old
// `normalize` function used to have a while loop to fold the u32,
// however, we can unroll that loop because we know ahead of time how
// much additions we need.
//
// 5. In the loop of `add_bytes`, the `adc_u64` is not used, instead,
// the `overflowing_add` is directly used. `adc_u64`'s carry flag
// comes from the current number being added while the slightly
// convoluted version in `add_bytes`, adding each number depends on
// the carry flag of the previous computation. I checked under release
// mode this issues 3 instructions instead of 4 for x86 and it should
// theoretically be beneficial, however, measurement showed me that it
// helps only a little. So this trick is not used for `update`.
//
// 6. When the input is small, fallback to deferred carry method. Deferred
// carry turns out to be very efficient when dealing with small buffers:
// If the input is small, the cost to deal with the tail may already
// outweigh the benefit of the unrolling itself. Some measurement
// confirms this theory.
//
// Results:
//
// Micro-benchmarks are run on an x86-64 gLinux workstation. In summary,
// compared the baseline 0 which is prior to the byteorder independence
// patch, there is a ~4x speedup.
//
// TODO: run this optimization on other platforms. I would expect
// the situation on ARM a bit different because I am not sure
// how much penalty there will be for misaligned read on ARM, or
// whether it is even supported (On x86 there is generally no
// penalty for misaligned read). If there will be penalties, we
// should consider alignment as an optimization opportunity on ARM.
// TODO(joshlf): Right-justify the columns above
#![cfg_attr(feature = "benchmark", feature(test))]
#[cfg(all(test, feature = "benchmark"))]
extern crate test;
// TODO(joshlf):
// - Investigate optimizations proposed in RFC 1071 Section 2. The most
// promising on modern hardware is probably (C) Parallel Summation, although
// that needs to be balanced against (1) Deferred Carries. Benchmarks will
// need to be performed to determine which is faster in practice, and under
// what scenarios.
/// Compute the checksum of "bytes".
///
/// `checksum(bytes)` is shorthand for:
///
/// ```rust
/// # use internet_checksum::Checksum;
/// # let bytes = &[];
/// # let _ = {
/// let mut c = Checksum::new();
/// c.add_bytes(bytes);
/// c.checksum()
/// # };
/// ```
#[inline]
pub fn checksum(bytes: &[u8]) -> [u8; 2] {
let mut c = Checksum::new();
c.add_bytes(bytes);
c.checksum()
}
#[cfg(target_arch = "x86_64")]
type Accumulator = u128;
#[cfg(not(target_arch = "x86_64"))]
type Accumulator = u64;
/// The threshold for small buffers, if the buffer is too small,
/// fall back to the normal deferred carry method where a wide
/// accumulator is used but one `u16` is added once at a time.
// TODO: `64` works fine on x86_64, but this value may be different
// on other platforms.
const SMALL_BUF_THRESHOLD: usize = 64;
/// The following macro unrolls operations on u16's to wider integers.
///
/// # Arguments
///
/// * `$arr` - The byte slice being processed.
/// * `$body` - The operation to operate on the wider integer. It should
/// be a macro because functions are not options here.
///
///
/// This macro will choose the "wide integer" for you, on x86-64,
/// it will choose u128 as the "wide integer" and u64 anywhere else.
macro_rules! loop_unroll {
(@inner $arr: ident, 16, $body:ident) => {
while $arr.len() >= 16 {
$body!(16, u128);
}
unroll_tail!($arr, 16, $body);
};
(@inner $arr: ident, 8, $body:ident) => {
while $arr.len() >= 8 {
$body!(8, u64);
}
unroll_tail!($arr, 8, $body);
};
($arr: ident, $body: ident) => {
#[cfg(target_arch = "x86_64")]
loop_unroll!(@inner $arr, 16, $body);
#[cfg(not(target_arch = "x86_64"))]
loop_unroll!(@inner $arr, 8, $body);
};
}
/// At the the end of loop unrolling, we have to take care of bytes
/// that are left over. For example, `unroll_tail!(bytes, 4, body)`
/// expands to
/// ```
/// if bytes.len & 2 != 0 {
/// body!(2, u16);
/// }
/// ```
macro_rules! unroll_tail {
($arr: ident, $n: literal, $read: ident, $body: ident) => {
if $arr.len() & $n != 0 {
$body!($n, $read);
}
};
($arr: ident, 4, $body: ident) => {
unroll_tail!($arr, 2, u16, $body);
};
($arr: ident, 8, $body: ident) => {
unroll_tail!($arr, 4, u32, $body);
unroll_tail!($arr, 4, $body);
};
($arr: ident, 16, $body: ident) => {
unroll_tail!($arr, 8, u64, $body);
unroll_tail!($arr, 8, $body);
};
}
/// Updates bytes in an existing checksum.
///
/// `update` updates a checksum to reflect that the already-checksummed bytes
/// `old` have been updated to contain the values in `new`. It implements the
/// algorithm described in Equation 3 in [RFC 1624]. The first byte must be at
/// an even number offset in the original input. If an odd number offset byte
/// needs to be updated, the caller should simply include the preceding byte as
/// well. If an odd number of bytes is given, it is assumed that these are the
/// last bytes of the input. If an odd number of bytes in the middle of the
/// input needs to be updated, the preceding or following byte of the input
/// should be added to make an even number of bytes.
///
/// # Panics
///
/// `update` panics if `old.len() != new.len()`.
///
/// [RFC 1624]: https://tools.ietf.org/html/rfc1624
#[inline]
pub fn update(checksum: [u8; 2], old: &[u8], new: &[u8]) -> [u8; 2] {
assert_eq!(old.len(), new.len());
// We compute on the sum, not the one's complement of the sum. checksum
// is the one's complement of the sum, so we need to get back to the
// sum. Thus, we negate checksum.
// HC' = ~HC
let mut sum = !u16::from_ne_bytes(checksum) as Accumulator;
// Let's reuse `Checksum::add_bytes` to update our checksum
// so that we can get the speedup for free. Using
// [RFC 1071 Eqn. 3], we can efficiently update our new checksum.
let mut c1 = Checksum::new();
let mut c2 = Checksum::new();
c1.add_bytes(old);
c2.add_bytes(new);
// Note, `c1.checksum_inner()` is actually ~m in [Eqn. 3]
// `c2.checksum_inner()` is actually ~m' in [Eqn. 3]
// so we have to negate `c2.checksum_inner()` first to get m'.
// HC' += ~m, c1.checksum_inner() == ~m.
sum = adc_accumulator(sum, c1.checksum_inner() as Accumulator);
// HC' += m', c2.checksum_inner() == ~m'.
sum = adc_accumulator(sum, !c2.checksum_inner() as Accumulator);
// HC' = ~HC.
(!normalize(sum)).to_ne_bytes()
}
/// RFC 1071 "internet checksum" computation.
///
/// `Checksum` implements the "internet checksum" defined in [RFC 1071] and
/// updated in [RFC 1141] and [RFC 1624], which is used by many different
/// protocols' packet formats. The checksum operates by computing the 1s
/// complement of the 1s complement sum of successive 16-bit words of the input.
///
/// [RFC 1071]: https://tools.ietf.org/html/rfc1071
/// [RFC 1141]: https://tools.ietf.org/html/rfc1141
/// [RFC 1624]: https://tools.ietf.org/html/rfc1624
#[derive(Default)]
pub struct Checksum {
sum: Accumulator,
// Since odd-length inputs are treated specially, we store the trailing byte
// for use in future calls to add_bytes(), and only treat it as a true
// trailing byte in checksum().
trailing_byte: Option<u8>,
}
impl Checksum {
/// Initialize a new checksum.
#[inline]
pub const fn new() -> Self {
Checksum { sum: 0, trailing_byte: None }
}
/// Add bytes to the checksum.
///
/// If `bytes` does not contain an even number of bytes, a single zero byte
/// will be added to the end before updating the checksum.
///
/// Note that `add_bytes` has some fixed overhead regardless of the size of
/// `bytes`. Where performance is a concern, prefer fewer calls to
/// `add_bytes` with larger input over more calls with smaller input.
#[inline]
pub fn add_bytes(&mut self, mut bytes: &[u8]) {
if bytes.len() < SMALL_BUF_THRESHOLD {
self.add_bytes_small(bytes);
return;
}
let mut sum = self.sum;
let mut carry = false;
// We are not using `adc_uXX` functions here, instead, we manually track
// the carry flag. This is because in `adc_uXX` functions, the carry
// flag depends on addition itself. So the assembly for that function
// reads as follows:
//
// mov %rdi, %rcx
// mov %rsi, %rax
// add %rcx, %rsi -- waste! only used to generate CF.
// adc %rdi, $rax -- the real useful instruction.
//
// So we had better to make us depend on the CF generated by the
// addition of the previous 16-bit word. The ideal assembly should look
// like:
//
// add 0(%rdi), %rax
// adc 8(%rdi), %rax
// adc 16(%rdi), %rax
// .... and so on ...
//
// Sadly, there are too many instructions that can affect the carry
// flag, and LLVM is not that optimized to find out the pattern and let
// all these adc instructions not interleaved. However, doing so results
// in 3 instructions instead of the original 4 instructions (the two
// mov's are still there) and it makes a difference on input size like
// 1023.
// The following macro is used as a `body` when invoking a `loop_unroll`
// macro. `$step` means how many bytes to handle at once; `$read` is
// supposed to be `u16`, `u32` and so on, it is used to get an unsigned
// integer of `$step` width from a byte slice; `$bytes` is the byte
// slice mentioned before, if omitted, it defaults to be `bytes`, which
// is the argument of the surrounding function.
macro_rules! update_sum_carry {
($step: literal, $ty: ident, $bytes: expr) => {
let (s, c) = sum
.overflowing_add($ty::from_ne_bytes($bytes.try_into().unwrap()) as Accumulator);
sum = s.wrapping_add(carry as Accumulator);
carry = c;
bytes = &bytes[$step..];
};
($step: literal, $ty: ident) => {
update_sum_carry!($step, $ty, bytes[..$step]);
};
}
// if there's a trailing byte, consume it first
if let Some(byte) = self.trailing_byte {
update_sum_carry!(1, u16, [byte, bytes[0]]);
self.trailing_byte = None;
}
loop_unroll!(bytes, update_sum_carry);
if bytes.len() == 1 {
self.trailing_byte = Some(bytes[0]);
}
self.sum = sum + (carry as Accumulator);
}
/// The efficient fallback when the buffer is small.
///
/// In this implementation, one `u16` is added once a
/// time, so we don't waste time on dealing with the
/// tail of the buffer. Besides, given that the accumulator
/// is large enough, when inputs are small, there should
/// hardly be overflows, so for any modern architecture,
/// there is little chance in misprediction.
// The inline attribute is needed here, micro benchmarks showed
// that it speeds up things.
#[inline(always)]
fn add_bytes_small(&mut self, mut bytes: &[u8]) {
if bytes.is_empty() {
return;
}
let mut sum = self.sum;
fn update_sum(acc: Accumulator, rhs: u16) -> Accumulator {
if let Some(updated) = acc.checked_add(rhs as Accumulator) {
updated
} else {
(normalize(acc) + rhs) as Accumulator
}
}
if let Some(byte) = self.trailing_byte {
sum = update_sum(sum, u16::from_ne_bytes([byte, bytes[0]]));
bytes = &bytes[1..];
self.trailing_byte = None;
}
bytes.chunks(2).for_each(|chunk| match chunk {
[byte] => self.trailing_byte = Some(*byte),
[first, second] => {
sum = update_sum(sum, u16::from_ne_bytes([*first, *second]));
}
bytes => unreachable!("{:?}", bytes),
});
self.sum = sum;
}
/// Computes the checksum, but in big endian byte order.
fn checksum_inner(&self) -> u16 {
let mut sum = self.sum;
if let Some(byte) = self.trailing_byte {
sum = adc_accumulator(sum, u16::from_ne_bytes([byte, 0]) as Accumulator);
}
!normalize(sum)
}
/// Computes the checksum, and returns the array representation.
///
/// `checksum` returns the checksum of all data added using `add_bytes` so
/// far. Calling `checksum` does *not* reset the checksum. More bytes may be
/// added after calling `checksum`, and they will be added to the checksum
/// as expected.
///
/// If an odd number of bytes have been added so far, the checksum will be
/// computed as though a single 0 byte had been added at the end in order to
/// even out the length of the input.
#[inline]
pub fn checksum(&self) -> [u8; 2] {
self.checksum_inner().to_ne_bytes()
}
}
macro_rules! impl_adc {
($name: ident, $t: ty) => {
/// implements 1's complement addition for $t,
/// exploiting the carry flag on a 2's complement machine.
/// In practice, the adc instruction will be generated.
fn $name(a: $t, b: $t) -> $t {
let (s, c) = a.overflowing_add(b);
s + (c as $t)
}
};
}
impl_adc!(adc_u16, u16);
impl_adc!(adc_u32, u32);
#[cfg(target_arch = "x86_64")]
impl_adc!(adc_u64, u64);
impl_adc!(adc_accumulator, Accumulator);
/// Normalizes the accumulator by mopping up the
/// overflow until it fits in a `u16`.
fn normalize(a: Accumulator) -> u16 {
#[cfg(target_arch = "x86_64")]
return normalize_64(adc_u64(a as u64, (a >> 64) as u64));
#[cfg(not(target_arch = "x86_64"))]
return normalize_64(a);
}
fn normalize_64(a: u64) -> u16 {
let t = adc_u32(a as u32, (a >> 32) as u32);
adc_u16(t as u16, (t >> 16) as u16)
}
#[cfg(all(test, feature = "benchmark"))]
mod benchmarks {
extern crate test;
use super::*;
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 31 bytes.
#[bench]
fn bench_checksum_31(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 31]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 32 bytes.
#[bench]
fn bench_checksum_32(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 32]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 64 bytes.
#[bench]
fn bench_checksum_64(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 64]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 128 bytes.
#[bench]
fn bench_checksum_128(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 128]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 256 bytes.
#[bench]
fn bench_checksum_256(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 256]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 1024 bytes.
#[bench]
fn bench_checksum_1024(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 1024]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
/// Benchmark time to calculate checksum with a single call to `add_bytes`
/// with 1023 bytes.
#[bench]
fn bench_checksum_1023(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 1023]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
#[bench]
fn bench_checksum_20(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 20]);
let mut c = Checksum::new();
c.add_bytes(&buf);
test::black_box(c.checksum());
});
}
#[bench]
fn bench_checksum_small_20(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 20]);
let mut c = Checksum::new();
c.add_bytes_small(&buf);
test::black_box(c.checksum());
});
}
#[bench]
fn bench_checksum_small_31(b: &mut test::Bencher) {
b.iter(|| {
let buf = test::black_box([0xFF; 31]);
let mut c = Checksum::new();
c.add_bytes_small(&buf);
test::black_box(c.checksum());
});
}
#[bench]
fn bench_update_2(b: &mut test::Bencher) {
b.iter(|| {
let old = test::black_box([0x42; 2]);
let new = test::black_box([0xa0; 2]);
test::black_box(update([42; 2], &old[..], &new[..]));
});
}
#[bench]
fn bench_update_4(b: &mut test::Bencher) {
b.iter(|| {
let old = test::black_box([0x42; 4]);
let new = test::black_box([0xa0; 4]);
test::black_box(update([42; 2], &old[..], &new[..]));
});
}
#[bench]
fn bench_update_8(b: &mut test::Bencher) {
b.iter(|| {
let old = test::black_box([0x42; 8]);
let new = test::black_box([0xa0; 8]);
test::black_box(update([42; 2], &old[..], &new[..]));
});
}
}
#[cfg(test)]
mod tests {
use rand::{Rng, SeedableRng};
use rand_xorshift::XorShiftRng;
use super::*;
/// Create a new deterministic RNG from a seed.
fn new_rng(mut seed: u128) -> XorShiftRng {
if seed == 0 {
// XorShiftRng can't take 0 seeds
seed = 1;
}
XorShiftRng::from_seed(seed.to_ne_bytes())
}
#[test]
fn test_checksum() {
for buf in IPV4_HEADERS {
// compute the checksum as normal
let mut c = Checksum::new();
c.add_bytes(&buf);
assert_eq!(c.checksum(), [0u8; 2]);
// compute the checksum one byte at a time to make sure our
// trailing_byte logic works
let mut c = Checksum::new();
for byte in *buf {
c.add_bytes(&[*byte]);
}
assert_eq!(c.checksum(), [0u8; 2]);
// Make sure that it works even if we overflow u32. Performing this
// loop 2 * 2^16 times is guaranteed to cause such an overflow
// because 0xFFFF + 0xFFFF > 2^16, and we're effectively adding
// (0xFFFF + 0xFFFF) 2^16 times. We verify the overflow as well by
// making sure that, at least once, the sum gets smaller from one
// loop iteration to the next.
let mut c = Checksum::new();
c.add_bytes(&[0xFF, 0xFF]);
for _ in 0..((2 * (1 << 16)) - 1) {
c.add_bytes(&[0xFF, 0xFF]);
}
assert_eq!(c.checksum(), [0u8; 2]);
}
}
#[test]
fn test_update() {
for b in IPV4_HEADERS {
let mut buf = Vec::new();
buf.extend_from_slice(b);
let mut c = Checksum::new();
c.add_bytes(&buf);
assert_eq!(c.checksum(), [0u8; 2]);
// replace the destination IP with the loopback address
let old = [buf[16], buf[17], buf[18], buf[19]];
(&mut buf[16..20]).copy_from_slice(&[127, 0, 0, 1]);
let updated = update(c.checksum(), &old, &[127, 0, 0, 1]);
let from_scratch = {
let mut c = Checksum::new();
c.add_bytes(&buf);
c.checksum()
};
assert_eq!(updated, from_scratch);
}
}
#[test]
fn test_update_noop() {
for b in IPV4_HEADERS {
let mut buf = Vec::new();
buf.extend_from_slice(b);
let mut c = Checksum::new();
c.add_bytes(&buf);
assert_eq!(c.checksum(), [0u8; 2]);
// Replace the destination IP with the same address. I.e. this
// update should be a no-op.
let old = [buf[16], buf[17], buf[18], buf[19]];
let updated = update(c.checksum(), &old, &old);
let from_scratch = {
let mut c = Checksum::new();
c.add_bytes(&buf);
c.checksum()
};
assert_eq!(updated, from_scratch);
}
}
#[test]
fn test_smoke_update() {
let mut rng = new_rng(70_812_476_915_813);
for _ in 0..2048 {
// use an odd length so we test the odd length logic
const BUF_LEN: usize = 31;
let buf: [u8; BUF_LEN] = rng.gen();
let mut c = Checksum::new();
c.add_bytes(&buf);
let (begin, end) = loop {
let begin = rng.gen::<usize>() % BUF_LEN;
let end = begin + (rng.gen::<usize>() % (BUF_LEN + 1 - begin));
// update requires that begin is even and end is either even or
// the end of the input
if begin % 2 == 0 && (end % 2 == 0 || end == BUF_LEN) {
break (begin, end);
}
};
let mut new_buf = buf;
for i in begin..end {
new_buf[i] = rng.gen();
}
let updated = update(c.checksum(), &buf[begin..end], &new_buf[begin..end]);
let from_scratch = {
let mut c = Checksum::new();
c.add_bytes(&new_buf);
c.checksum()
};
assert_eq!(updated, from_scratch);
}
}
#[test]
fn test_add_bytes_small_prop_test() {
// Since we have two independent implementations
// Now it is time for us to write a property test
// to ensure the checksum algorithm(s) are indeed correct.
let mut rng = new_rng(123478012483);
let mut c1 = Checksum::new();
let mut c2 = Checksum::new();
for len in 64..1_025 {
for _ in 0..4 {
let mut buf = vec![];
for _ in 0..len {
buf.push(rng.gen());
}
c1.add_bytes(&buf[..]);
c2.add_bytes_small(&buf[..]);
assert_eq!(c1.checksum(), c2.checksum());
let n1 = c1.checksum_inner();
let n2 = c2.checksum_inner();
assert_eq!(n1, n2);
let mut t1 = Checksum::new();
let mut t2 = Checksum::new();
let mut t3 = Checksum::new();
t3.add_bytes(&buf[..]);
if buf.len() % 2 == 1 {
buf.push(0);
}
assert_eq!(buf.len() % 2, 0);
buf.extend_from_slice(&t3.checksum());
t1.add_bytes(&buf[..]);
t2.add_bytes_small(&buf[..]);
assert_eq!(t1.checksum(), [0, 0]);
assert_eq!(t2.checksum(), [0, 0]);
}
}
}
/// IPv4 headers.
///
/// This data was obtained by capturing live network traffic.
const IPV4_HEADERS: &[&[u8]] = &[
&[
0x45, 0x00, 0x00, 0x34, 0x00, 0x00, 0x40, 0x00, 0x40, 0x06, 0xae, 0xea, 0xc0, 0xa8,
0x01, 0x0f, 0xc0, 0xb8, 0x09, 0x6a,
],
&[
0x45, 0x20, 0x00, 0x74, 0x5b, 0x6e, 0x40, 0x00, 0x37, 0x06, 0x5c, 0x1c, 0xc0, 0xb8,
0x09, 0x6a, 0xc0, 0xa8, 0x01, 0x0f,
],
&[
0x45, 0x20, 0x02, 0x8f, 0x00, 0x00, 0x40, 0x00, 0x3b, 0x11, 0xc9, 0x3f, 0xac, 0xd9,
0x05, 0x6e, 0xc0, 0xa8, 0x01, 0x0f,
],
];
// This test checks that an input, found by a fuzzer, no longer causes a crash due to addition
// overflow.
#[test]
fn test_large_buffer_addition_overflow() {
let mut sum = Checksum { sum: 0, trailing_byte: None };
let bytes = [
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
];
sum.add_bytes(&bytes[..]);
}
}