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  1. 2
      Cargo.toml
  2. 69
      src/lib.rs

2
Cargo.toml

@ -1,6 +1,6 @@
[package] [package]
name = "const-crc32" name = "const-crc32"
version = "1.3.0" version = "1.3.0-rc.1"
edition = "2021" edition = "2021"
authors = ["Jonathan Strong <jstrong@shipyard.rs>"] authors = ["Jonathan Strong <jstrong@shipyard.rs>"]
license = "MIT" license = "MIT"

69
src/lib.rs

@ -10,7 +10,6 @@
/// used to generate up a [u32; 256] lookup table in `crc32`. this computes /// used to generate up a [u32; 256] lookup table in `crc32`. this computes
/// the table on demand for a given "index" `i` /// the table on demand for a given "index" `i`
#[rustfmt::skip]
const fn table_fn(i: u32) -> u32 { const fn table_fn(i: u32) -> u32 {
let mut out = i; let mut out = i;
@ -49,40 +48,6 @@ pub const fn crc32(buf: &[u8]) -> u32 {
crc32_seed(buf, 0) crc32_seed(buf, 0)
} }
/// Calculate crc32 checksum, using provided `seed` as the initial state, instead of the
/// default initial state of `0u32`.
///
/// # Examples
///
/// Calculating the checksum from several parts of a larger input:
///
/// ```
/// const BYTES: &[u8] = "The quick brown fox jumps over the lazy dog".as_bytes();
///
/// let mut cksum = 0u32;
///
/// cksum = const_crc32::crc32_seed(&BYTES[0..10], cksum);
/// cksum = const_crc32::crc32_seed(&BYTES[10..15], cksum);
/// cksum = const_crc32::crc32_seed(&BYTES[15..], cksum);
///
/// assert_eq!(cksum, const_crc32::crc32(BYTES));
/// ```
///
/// Using separate seeds for different kinds of data, to produce different checksums depending
/// on what kind of data the bytes represent:
///
/// ```
/// const THING_ONE_SEED: u32 = 0xbaaaaaad_u32;
/// const THING_TWO_SEED: u32 = 0x2bad2bad_u32;
///
/// let thing_one_bytes = "bump! thump!".as_bytes();
/// let thing_two_bytes = "thump! bump!".as_bytes();
///
/// let thing_one_cksum = const_crc32::crc32_seed(thing_one_bytes, THING_ONE_SEED);
/// let thing_two_cksum = const_crc32::crc32_seed(thing_two_bytes, THING_TWO_SEED);
///
/// assert_ne!(thing_one_cksum, thing_two_cksum);
/// ```
#[inline] #[inline]
pub const fn crc32_seed(buf: &[u8], seed: u32) -> u32 { pub const fn crc32_seed(buf: &[u8], seed: u32) -> u32 {
let mut out = !seed; let mut out = !seed;
@ -102,10 +67,12 @@ mod tests {
fn crc32_compute_table() -> [u32; 256] { fn crc32_compute_table() -> [u32; 256] {
let mut crc32_table = [0; 256]; let mut crc32_table = [0; 256];
for n in 0..256_u32 { for n in 0..256 {
crc32_table[n as usize] = (0..8).fold(n, |acc, _| match acc & 1 { crc32_table[n as usize] = (0..8).fold(n as u32, |acc, _| {
1 => 0xedb88320 ^ (acc >> 1), match acc & 1 {
_ => acc >> 1, 1 => 0xedb88320 ^ (acc >> 1),
_ => acc >> 1,
}
}); });
} }
@ -115,7 +82,7 @@ mod tests {
#[test] #[test]
fn check_table_fn_against_example_code() { fn check_table_fn_against_example_code() {
let table = crc32_compute_table(); let table = crc32_compute_table();
for i in 0..256 { for i in 0..256{
assert_eq!(table[i], table_fn(i as u32)); assert_eq!(table[i], table_fn(i as u32));
} }
} }
@ -127,28 +94,6 @@ mod tests {
assert_eq!(crc32(BYTES), crc32fast::hash(BYTES)); assert_eq!(crc32(BYTES), crc32fast::hash(BYTES));
} }
#[test]
fn use_seed_to_checksum_from_partial_inputs() {
const BYTES: &[u8] = "The quick brown fox jumps over the lazy dog".as_bytes();
let mut cksum = crc32(&BYTES[0..10]);
cksum = crc32_seed(&BYTES[10..], cksum);
assert_eq!(cksum, crc32(BYTES));
}
#[test]
fn use_seed_to_checksum_from_many_chunks() {
let mut buf = [0u8; 1024];
let mut rng = thread_rng();
rng.fill(&mut buf[..]);
let mut cksum = 0;
for chunk in buf[..].chunks(7) {
cksum = crc32_seed(chunk, cksum);
}
assert_eq!(cksum, crc32(&buf[..]));
}
#[test] #[test]
fn check_random_inputs_against_crc32_fast() { fn check_random_inputs_against_crc32_fast() {
const N_ITER: usize = 100; const N_ITER: usize = 100;

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