Add non-breaking API for custom implementations

The previous attempt was a breaking change.

Signed-off-by: Akhil Velagapudi <4@4khil.com>

.github/workflows/ci.yaml

@@ -24,7 +24,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.56.0
+          - 1.65.0
           - stable
           - beta
     steps:

Cargo.toml

@@ -13,18 +13,7 @@ description = "Rust implementation of CRC with support of various standards"
 keywords = ["crc", "crc16", "crc32", "crc64", "hash"]
 categories = ["algorithms", "no-std"]
 edition = "2021"
-rust-version = "1.56"
-
-# [features]
-# use the "NoTable" implementation for the default Crc<uXXX> struct, using no additional memory for a lookup table.
-# Takes precedence over "bytewise-mem-limit" and "slice16-mem-limit"
-# no-table-mem-limit = []
-# use the "Bytewise" implementation for the default Crc<uXXX> struct, using 256 entries of the respective width for a lookup table.
-# Takes precedence over "slice16-mem-limit" and is used if no feature is selected
-# bytewise-mem-limit = []
-# use the "Slice16" implementation for the default Crc<uXXX> struct, using 256 * 16 entries of the respective width for a lookup table.
-# Can be overriden by setting "bytewise-mem-limit" and "slice16-mem-limit"
-# slice16-mem-limit = []
+rust-version = "1.65"
 
 [dependencies]
 crc-catalog = "2.4.0"

README.md

@@ -43,29 +43,21 @@ assert_eq!(digest.finalize(), 0xaee7);
 
 ### Minimum supported Rust version (MSRV)
 
-This crate's MSRV is 1.56.
+This crate's MSRV is 1.65.
 
 At a minimum, the MSRV will be <= the oldest stable release in the last 12 months. MSRV may be bumped in minor version releases.
 
-### Lookup table flavors
+### Implementations
 
-This crate offers three flavors of lookup tables providing a tradeoff between computation speed and used memory.
-See the benchmark section for hints, but do benchmarks on your target hardware to decide if the tradeoff is worth it to you.
+This crate has several pluggable implementations:
 
-1. `NoTable` provides an implementation that uses no additional memory
-2. `Bytewise` provides an implementation that uses a lookup table that uses 256 entries of the used width (e.g. for u32 thats 256 * 4 bytes)
-3. `Slice16` provides an implementation that uses a lookup table that uses 16 * 256 entries of the used width (e.g. for u32 thats 16 * 256 * 4 bytes)
+1. `NoTable` doesn't use a lookup table, and thus minimizes binary size and memory usage.
+2. `Table<1>` uses a lookup table with 256 entries (e.g. for u32 thats 256 * 4 bytes).
+3. `Table<16>` uses a lookup table with 16 * 256 entries (e.g. for u32 thats 16 * 256 * 4 bytes).
 
-These can be used by substituting `Crc<uxxx>` with e.g. `Crc<Slice16<uxxx>>`. The flavor for `Crc<uxxx>` is chosen based on three crate features:
+`Table<1>` is the default implementation, but this can be overridden by specifying `I` in `Crc<W, I>`. E.g.: `Crc<u32, NoTable>`, `Crc<u64, Table<16>>`, ...
 
-* no-table-mem-limit: Takes precedence over "bytewise-mem-limit" or "slice16-mem-limit"
-* bytewise-mem-limit: Takes precedence over "slice16-mem-limit" and can be overridden by setting "no-table-mem-limit"
-* slice16-mem-limit: Can be overridden by setting "bytewise-mem-limit" or "no-table-mem-limit"
-
-If no feature is selected, the `Bytewise` flavor is used.
-
-Note that these tables can bloat your binary size if you precalculate them at compiletime (this happens in `Crc::new`). 
-Choosing a crate like oncecell or lazystatic to compute them once at runtime may be preferable where binary size is a concern.
+NOTE: Lookup tables will increase binary size if they're generated at compile-time. Wrapping `Crc` initialization in a `std::cell::OnceCell` may be preferable if binary size is a concern.
 
 ### Benchmark
 

benches/bench.rs

@@ -2,26 +2,26 @@ use crc::*;
 use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
 
 pub const BLUETOOTH: Crc<u8> = Crc::<u8>::new(&CRC_8_BLUETOOTH);
-pub const BLUETOOTH_SLICE16: Crc<Slice16<u8>> = Crc::<Slice16<u8>>::new(&CRC_8_BLUETOOTH);
-pub const BLUETOOTH_BYTEWISE: Crc<Bytewise<u8>> = Crc::<Bytewise<u8>>::new(&CRC_8_BLUETOOTH);
-pub const BLUETOOTH_NOLOOKUP: Crc<NoTable<u8>> = Crc::<NoTable<u8>>::new(&CRC_8_BLUETOOTH);
+pub const BLUETOOTH_SLICE16: Crc<u8, Table<16>> = Crc::<u8, Table<16>>::new(&CRC_8_BLUETOOTH);
+pub const BLUETOOTH_BYTEWISE: Crc<u8, Table<1>> = Crc::<u8, Table<1>>::new(&CRC_8_BLUETOOTH);
+pub const BLUETOOTH_NOLOOKUP: Crc<u8, NoTable> = Crc::<u8, NoTable>::new(&CRC_8_BLUETOOTH);
 pub const X25: Crc<u16> = Crc::<u16>::new(&CRC_16_IBM_SDLC);
-pub const X25_SLICE16: Crc<Slice16<u16>> = Crc::<Slice16<u16>>::new(&CRC_16_IBM_SDLC);
-pub const X25_BYTEWISE: Crc<Bytewise<u16>> = Crc::<Bytewise<u16>>::new(&CRC_16_IBM_SDLC);
-pub const X25_NOLOOKUP: Crc<NoTable<u16>> = Crc::<NoTable<u16>>::new(&CRC_16_IBM_SDLC);
+pub const X25_SLICE16: Crc<u16, Table<16>> = Crc::<u16, Table<16>>::new(&CRC_16_IBM_SDLC);
+pub const X25_BYTEWISE: Crc<u16, Table<1>> = Crc::<u16, Table<1>>::new(&CRC_16_IBM_SDLC);
+pub const X25_NOLOOKUP: Crc<u16, NoTable> = Crc::<u16, NoTable>::new(&CRC_16_IBM_SDLC);
 pub const ISCSI: Crc<u32> = Crc::<u32>::new(&CRC_32_ISCSI);
-pub const ISCSI_SLICE16: Crc<Slice16<u32>> = Crc::<Slice16<u32>>::new(&CRC_32_ISCSI);
-pub const ISCSI_BYTEWISE: Crc<Bytewise<u32>> = Crc::<Bytewise<u32>>::new(&CRC_32_ISCSI);
-pub const ISCSI_NOLOOKUP: Crc<NoTable<u32>> = Crc::<NoTable<u32>>::new(&CRC_32_ISCSI);
+pub const ISCSI_SLICE16: Crc<u32, Table<16>> = Crc::<u32, Table<16>>::new(&CRC_32_ISCSI);
+pub const ISCSI_BYTEWISE: Crc<u32, Table<1>> = Crc::<u32, Table<1>>::new(&CRC_32_ISCSI);
+pub const ISCSI_NOLOOKUP: Crc<u32, NoTable> = Crc::<u32, NoTable>::new(&CRC_32_ISCSI);
 pub const GSM_40: Crc<u64> = Crc::<u64>::new(&CRC_40_GSM);
 pub const ECMA: Crc<u64> = Crc::<u64>::new(&CRC_64_ECMA_182);
-pub const ECMA_SLICE16: Crc<Slice16<u64>> = Crc::<Slice16<u64>>::new(&CRC_64_ECMA_182);
-pub const ECMA_BYTEWISE: Crc<Bytewise<u64>> = Crc::<Bytewise<u64>>::new(&CRC_64_ECMA_182);
-pub const ECMA_NOLOOKUP: Crc<NoTable<u64>> = Crc::<NoTable<u64>>::new(&CRC_64_ECMA_182);
+pub const ECMA_SLICE16: Crc<u64, Table<16>> = Crc::<u64, Table<16>>::new(&CRC_64_ECMA_182);
+pub const ECMA_BYTEWISE: Crc<u64, Table<1>> = Crc::<u64, Table<1>>::new(&CRC_64_ECMA_182);
+pub const ECMA_NOLOOKUP: Crc<u64, NoTable> = Crc::<u64, NoTable>::new(&CRC_64_ECMA_182);
 pub const DARC: Crc<u128> = Crc::<u128>::new(&CRC_82_DARC);
-pub const DARC_SLICE16: Crc<Slice16<u128>> = Crc::<Slice16<u128>>::new(&CRC_82_DARC);
-pub const DARC_BYTEWISE: Crc<Bytewise<u128>> = Crc::<Bytewise<u128>>::new(&CRC_82_DARC);
-pub const DARC_NOLOOKUP: Crc<NoTable<u128>> = Crc::<NoTable<u128>>::new(&CRC_82_DARC);
+pub const DARC_SLICE16: Crc<u128, Table<16>> = Crc::<u128, Table<16>>::new(&CRC_82_DARC);
+pub const DARC_BYTEWISE: Crc<u128, Table<1>> = Crc::<u128, Table<1>>::new(&CRC_82_DARC);
+pub const DARC_NOLOOKUP: Crc<u128, NoTable> = Crc::<u128, NoTable>::new(&CRC_82_DARC);
 
 static KB: usize = 1024;
 

src/crc128.rs

@@ -2,7 +2,6 @@ use crate::util::crc128;
 use crc_catalog::Algorithm;
 
 mod bytewise;
-mod default;
 mod nolookup;
 mod slice16;
 
@@ -169,100 +168,9 @@ const fn update_slice16(
 
 #[cfg(test)]
 mod test {
-    use crate::{Bytewise, Crc, Implementation, NoTable, Slice16};
+    use crate::*;
     use crc_catalog::{Algorithm, CRC_82_DARC};
 
-    #[test]
-    fn default_table_size() {
-        const TABLE_SIZE: usize = core::mem::size_of::<<u128 as Implementation>::Table>();
-        const BYTES_PER_ENTRY: usize = 16;
-        #[cfg(all(
-            feature = "no-table-mem-limit",
-            feature = "bytewise-mem-limit",
-            feature = "slice16-mem-limit"
-        ))]
-        {
-            const EXPECTED: usize = 0;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-        #[cfg(all(
-            feature = "no-table-mem-limit",
-            feature = "bytewise-mem-limit",
-            not(feature = "slice16-mem-limit")
-        ))]
-        {
-            const EXPECTED: usize = 0;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-        #[cfg(all(
-            feature = "no-table-mem-limit",
-            not(feature = "bytewise-mem-limit"),
-            feature = "slice16-mem-limit"
-        ))]
-        {
-            const EXPECTED: usize = 0;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-        #[cfg(all(
-            feature = "no-table-mem-limit",
-            not(feature = "bytewise-mem-limit"),
-            not(feature = "slice16-mem-limit")
-        ))]
-        {
-            const EXPECTED: usize = 0;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-
-        #[cfg(all(
-            not(feature = "no-table-mem-limit"),
-            feature = "bytewise-mem-limit",
-            feature = "slice16-mem-limit"
-        ))]
-        {
-            const EXPECTED: usize = 256 * BYTES_PER_ENTRY;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-        #[cfg(all(
-            not(feature = "no-table-mem-limit"),
-            feature = "bytewise-mem-limit",
-            not(feature = "slice16-mem-limit")
-        ))]
-        {
-            const EXPECTED: usize = 256 * BYTES_PER_ENTRY;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-
-        #[cfg(all(
-            not(feature = "no-table-mem-limit"),
-            not(feature = "bytewise-mem-limit"),
-            feature = "slice16-mem-limit"
-        ))]
-        {
-            const EXPECTED: usize = 256 * 16 * BYTES_PER_ENTRY;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-
-        #[cfg(all(
-            not(feature = "no-table-mem-limit"),
-            not(feature = "bytewise-mem-limit"),
-            not(feature = "slice16-mem-limit")
-        ))]
-        {
-            const EXPECTED: usize = 256 * BYTES_PER_ENTRY;
-            let _ = EXPECTED;
-            const _: () = assert!(EXPECTED == TABLE_SIZE);
-        }
-        let _ = TABLE_SIZE;
-        let _ = BYTES_PER_ENTRY;
-    }
-
     /// Test this optimized version against the well known implementation to ensure correctness
     #[test]
     fn correctness() {
@@ -291,9 +199,9 @@ mod test {
 
         for alg in algs_to_test {
             for data in data {
-                let crc_slice16 = Crc::<Slice16<u128>>::new(alg);
-                let crc_nolookup = Crc::<NoTable<u128>>::new(alg);
-                let expected = Crc::<Bytewise<u128>>::new(alg).checksum(data.as_bytes());
+                let crc_slice16 = Crc::<u128, Table<16>>::new(alg);
+                let crc_nolookup = Crc::<u128, NoTable>::new(alg);
+                let expected = Crc::<u128, Table<1>>::new(alg).checksum(data.as_bytes());
 
                 // Check that doing all at once works as expected
                 assert_eq!(crc_slice16.checksum(data.as_bytes()), expected);

src/crc128/bytewise.rs

@@ -1,12 +1,15 @@
 use crate::table::crc128_table;
-use crate::{Algorithm, Bytewise, Crc, Digest};
+use crate::*;
 
 use super::{finalize, init, update_bytewise};
 
-impl Crc<Bytewise<u128>> {
+impl Crc<u128, Table<1>> {
     pub const fn new(algorithm: &'static Algorithm<u128>) -> Self {
         let table = crc128_table(algorithm.width, algorithm.poly, algorithm.refin);
-        Self { algorithm, table }
+        Self {
+            algorithm,
+            data: [table],
+        }
     }
 
     pub const fn checksum(&self, bytes: &[u8]) -> u128 {
@@ -16,10 +19,10 @@ impl Crc<Bytewise<u128>> {
     }
 
     const fn update(&self, crc: u128, bytes: &[u8]) -> u128 {
-        update_bytewise(crc, self.algorithm.refin, &self.table, bytes)
+        update_bytewise(crc, self.algorithm.refin, &self.data[0], bytes)
     }
 
-    pub const fn digest(&self) -> Digest<Bytewise<u128>> {
+    pub const fn digest(&self) -> Digest<u128, Table<1>> {
         self.digest_with_initial(self.algorithm.init)
     }
 
@@ -28,14 +31,14 @@ impl Crc<Bytewise<u128>> {
     /// This overrides the initial value specified by the algorithm.
     /// The effects of the algorithm's properties `refin` and `width`
     /// are applied to the custom initial value.
-    pub const fn digest_with_initial(&self, initial: u128) -> Digest<Bytewise<u128>> {
+    pub const fn digest_with_initial(&self, initial: u128) -> Digest<u128, Table<1>> {
         let value = init(self.algorithm, initial);
         Digest::new(self, value)
     }
 }
 
-impl<'a> Digest<'a, Bytewise<u128>> {
-    const fn new(crc: &'a Crc<Bytewise<u128>>, value: u128) -> Self {
+impl<'a> Digest<'a, u128, Table<1>> {
+    const fn new(crc: &'a Crc<u128, Table<1>>, value: u128) -> Self {
         Digest { crc, value }
     }