add docs and tests for `crc32_seed`
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src/lib.rs
56
src/lib.rs
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@ -48,6 +48,40 @@ pub const fn crc32(buf: &[u8]) -> u32 {
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crc32_seed(buf, 0)
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}
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/// Calculate crc32 checksum, using provided `seed` as the initial state, instead of the
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/// default initial state of `0u32`.
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///
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/// # Examples
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///
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/// Calculating the checksum from several parts of a larger input:
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///
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/// ```
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/// const BYTES: &[u8] = "The quick brown fox jumps over the lazy dog".as_bytes();
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///
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/// let mut cksum = 0u32;
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///
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/// cksum = const_crc32::crc32_seed(&BYTES[0..10], cksum);
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/// cksum = const_crc32::crc32_seed(&BYTES[10..15], cksum);
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/// cksum = const_crc32::crc32_seed(&BYTES[15..], cksum);
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///
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/// assert_eq!(cksum, const_crc32::crc32(BYTES));
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/// ```
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///
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/// Using separate seeds for different kinds of data, to produce different checksums depending
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/// on what kind of data the bytes represent:
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///
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/// ```
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/// const THING_ONE_SEED: u32 = 0xdeadbeef_u32;
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/// const THING_TWO_SEED: u32 = 0xbaaaaaad_u32;
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///
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/// let thing_one_bytes = "bump! thump!".as_bytes();
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/// let thing_two_bytes = "thump! bump!".as_bytes();
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///
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/// let thing_one_cksum = const_crc32::crc32_seed(thing_one_bytes, THING_ONE_SEED);
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/// let thing_two_cksum = const_crc32::crc32_seed(thing_two_bytes, THING_TWO_SEED);
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///
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/// assert_ne!(thing_one_cksum, thing_two_cksum);
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/// ```
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#[inline]
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pub const fn crc32_seed(buf: &[u8], seed: u32) -> u32 {
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let mut out = !seed;
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@ -94,6 +128,28 @@ mod tests {
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assert_eq!(crc32(BYTES), crc32fast::hash(BYTES));
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}
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#[test]
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fn use_seed_to_checksum_from_partial_inputs() {
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const BYTES: &[u8] = "The quick brown fox jumps over the lazy dog".as_bytes();
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let mut cksum = crc32(&BYTES[0..10]);
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cksum = crc32_seed(&BYTES[10..], cksum);
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assert_eq!(cksum, crc32(BYTES));
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}
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#[test]
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fn use_seed_to_checksum_from_many_chunks() {
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let mut buf = [0u8; 1024];
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let mut rng = thread_rng();
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rng.fill(&mut buf[..]);
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let mut cksum = 0;
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for chunk in buf[..].chunks(7) {
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cksum = crc32_seed(chunk, cksum);
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}
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assert_eq!(cksum, crc32(&buf[..]));
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}
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#[test]
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fn check_random_inputs_against_crc32_fast() {
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const N_ITER: usize = 100;
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