Crc final

final class Crc

Factory methods for creating CRC (Cyclic Redundancy Check) computation functions.

CRC is an error-detecting code commonly used to verify data integrity in digital networks and storage devices.

This class provides two levels of API:

• One-shot: Use crc8, crc16, crc24, crc32, or from to obtain a function that computes a CRC over a complete BitVector in a single call.
• Incremental: Use builder to create a CrcBuilder that can accumulate data in chunks before producing a final result.

final checksum = Crc.crc32(myData);

See also:

• CrcParams, which defines the parameters for specific CRC algorithms.
• CrcBuilder, for incremental CRC computation.

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);

Static Properties

crc16 no setter

BitVector Function(BitVector) get crc16

Returns a CRC-16/ARC computation function.

Each call creates a fresh function from CrcParams.crc16.

Implementation

static Function1<BitVector, BitVector> get crc16 => from(CrcParams.crc16());

crc24 no setter

BitVector Function(BitVector) get crc24

Returns a CRC-24/OpenPGP computation function.

Each call creates a fresh function from CrcParams.crc24.

Implementation

static Function1<BitVector, BitVector> get crc24 => from(CrcParams.crc24());

crc32 no setter

BitVector Function(BitVector) get crc32

Returns a CRC-32/ISO-HDLC computation function.

Each call creates a fresh function from CrcParams.crc32.

Implementation

static Function1<BitVector, BitVector> get crc32 => from(CrcParams.crc32());

crc8 no setter

BitVector Function(BitVector) get crc8

Returns a CRC-8/SMBUS computation function.

Each call creates a fresh function from CrcParams.crc8.

Implementation

static Function1<BitVector, BitVector> get crc8 => from(CrcParams.crc8());

Static Methods

builder()

CrcBuilder<BitVector> builder(
  BitVector poly,
  BitVector initial,
  bool reflectInput,
  bool reflectOutput,
  BitVector finalXor,
)

Creates a CrcBuilder for incremental CRC computation.

Use this when data arrives in chunks or when you need to inspect intermediate CRC state. A 256-entry lookup table is pre-computed from the given polynomial for efficient byte-at-a-time processing.

For polynomials narrower than 8 bits, the builder falls back to bitwise processing.

final bldr = Crc.builder(
  poly, initial, reflectInput, reflectOutput, finalXor,
);
final result = bldr.updated(chunk1).updated(chunk2).result();

Implementation

static CrcBuilder<BitVector> builder(
  BitVector poly,
  BitVector initial,
  bool reflectInput,
  bool reflectOutput,
  BitVector finalXor,
) {
  final table = Array.ofDim<BitVector>(256);

  final zeroed = BitVector.fill(poly.size - 8, false);
  const m = 8;

  for (int idx = 0; idx < table.length; idx++) {
    BitVector shift(int k0, BitVector crcreg0) {
      int k = k0;
      BitVector crcreg = crcreg0;

      while (k < m) {
        final shifted = crcreg << 1;
        k += 1;
        crcreg = crcreg.head ? shifted.xor(poly) : shifted;
      }

      return crcreg;
    }

    table[idx] = shift(0, ByteVector([idx]).bits.concat(zeroed)).compact();
  }

  return _GenericCrcBuilder(
    table,
    poly,
    initial,
    reflectInput,
    reflectOutput,
    finalXor,
  );
}

from()

BitVector Function(BitVector) from(CrcParams params)

Creates a one-shot CRC function from the given params.

The returned function accepts a BitVector and returns the computed CRC checksum as a BitVector whose size matches CrcParams.width.

Implementation

static Function1<BitVector, BitVector> from(CrcParams params) => Crc.of(
  params.poly,
  params.initial,
  params.reflectInput,
  params.reflectOutput,
  params.finalXor,
);

of()

BitVector Function(BitVector) of(
  BitVector poly,
  BitVector initial,
  bool reflectInput,
  bool reflectOutput,
  BitVector finalXor,
)

Creates a one-shot CRC function from individual CRC components.

All BitVector arguments must have the same BitVector.size.

Internally, this pre-computes a 256-entry lookup table for table-driven CRC computation and returns a closure that processes input data against that table.

Implementation

static Function1<BitVector, BitVector> of(
  BitVector poly,
  BitVector initial,
  bool reflectInput,
  bool reflectOutput,
  BitVector finalXor,
) {
  assert(poly.nonEmpty, 'empty polynomial');

  assert(
    initial.size == poly.size && poly.size == finalXor.size,
    'poly, initial and finalXor must be same length',
  );

  final bldr = builder(poly, initial, reflectInput, reflectOutput, finalXor);
  return (data) => bldr.updated(data).result();
}