bump version to v1.3.0

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "const-crc32"
-version = "1.2.0"
+version = "1.3.0"
 edition = "2021"
 authors = ["Jonathan Strong <jstrong@shipyard.rs>"]
 license = "MIT"

src/lib.rs

@@ -10,6 +10,7 @@
 
 /// used to generate up a [u32; 256] lookup table in `crc32`. this computes
 /// the table on demand for a given "index" `i`
+#[rustfmt::skip]
 const fn table_fn(i: u32) -> u32 {
     let mut out = i;
 
@@ -48,6 +49,40 @@ pub const fn crc32(buf: &[u8]) -> u32 {
     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]
 pub const fn crc32_seed(buf: &[u8], seed: u32) -> u32 {
     let mut out = !seed;
@@ -67,12 +102,10 @@ mod tests {
     fn crc32_compute_table() -> [u32; 256] {
         let mut crc32_table = [0; 256];
 
-        for n in 0..256 {
-            crc32_table[n as usize] = (0..8).fold(n as u32, |acc, _| {
-                match acc & 1 {
-                    1 => 0xedb88320 ^ (acc >> 1),
-                    _ => acc >> 1,
-                }
+        for n in 0..256_u32 {
+            crc32_table[n as usize] = (0..8).fold(n, |acc, _| match acc & 1 {
+                1 => 0xedb88320 ^ (acc >> 1),
+                _ => acc >> 1,
             });
         }
 
@@ -82,7 +115,7 @@ mod tests {
     #[test]
     fn check_table_fn_against_example_code() {
         let table = crc32_compute_table();
-        for i in 0..256{
+        for i in 0..256 {
             assert_eq!(table[i], table_fn(i as u32));
         }
     }
@@ -94,6 +127,28 @@ mod tests {
         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]
     fn check_random_inputs_against_crc32_fast() {
         const N_ITER: usize = 100;