CrcParams

class CrcParams

Parameters that fully define a CRC (Cyclic Redundancy Check) algorithm.

A CRC algorithm is determined by five values:

A generator polynomial.
An initial register value.
Whether to reflectInput bits within each byte before processing.
Whether to reflectOutput the final register before XOR.
A finalXor mask applied to the output.

Use the named factory constructors (e.g. CrcParams.crc32, CrcParams.crc16) to obtain parameters for well-known standards, or CrcParams.hex to build custom parameters from hex strings.

Pass a CrcParams to Crc.from to obtain a CRC computation function.

Constructors

CrcParams() const

const CrcParams(
  BitVector poly,
  BitVector initial,
  bool reflectInput,
  bool reflectOutput,
  BitVector finalXor,
)

Creates a CrcParams from the given component values.

All BitVector arguments (poly, initial, finalXor) must have the same BitVector.size.

Implementation

dart

const CrcParams(
  this.poly,
  this.initial,
  this.reflectInput,
  this.reflectOutput,
  this.finalXor,
);

CrcParams.crc8() factory

factory CrcParams.crc8()

Default CRC-8 parameters.

Alias for CrcParams.crc8SMBus.

Implementation

dart

factory CrcParams.crc8() => CrcParams.crc8SMBus();

CrcParams.crc8Rohc() factory

factory CrcParams.crc8Rohc()

CRC-8/ROHC parameters, used in Robust Header Compression.

Polynomial: 0x07
Initial: 0xFF
Reflect input/output: true
Final XOR: 0x00

Implementation

dart

factory CrcParams.crc8Rohc() => CrcParams.hex('0x07', '0xff', true, true, '0x00');

CrcParams.crc8SMBus() factory

factory CrcParams.crc8SMBus()

CRC-8/SMBUS parameters.

Polynomial: 0x07
Initial: 0x00
Reflect input/output: false
Final XOR: 0x00

Implementation

dart

factory CrcParams.crc8SMBus() => CrcParams.hex('0x07', '0x00', false, false, '0x00');

CrcParams.crc16() factory

factory CrcParams.crc16()

Default CRC-16 parameters.

Alias for CrcParams.crc16Arc.

Implementation

dart

factory CrcParams.crc16() => CrcParams.crc16Arc();

CrcParams.crc16Arc() factory

factory CrcParams.crc16Arc()

CRC-16/ARC parameters.

Polynomial: 0x8005
Initial: 0x0000
Reflect input/output: true
Final XOR: 0x0000

Implementation

dart

factory CrcParams.crc16Arc() => CrcParams.hex('0x8005', '0x0000', true, true, '0x0000');

CrcParams.crc16Kermit() factory

factory CrcParams.crc16Kermit()

CRC-16/Kermit parameters, used in the Kermit file transfer protocol.

Polynomial: 0x1021
Initial: 0x0000
Reflect input/output: true
Final XOR: 0x0000

Implementation

dart

factory CrcParams.crc16Kermit() => CrcParams.hex('0x1021', '0x0000', true, true, '0x0000');

CrcParams.crc24() factory

factory CrcParams.crc24()

Default CRC-24 parameters.

Alias for CrcParams.crc24OpenPgp.

Implementation

dart

factory CrcParams.crc24() => CrcParams.crc24OpenPgp();

CrcParams.crc24OpenPgp() factory

factory CrcParams.crc24OpenPgp()

CRC-24/OpenPGP parameters, as defined in RFC 4880.

Polynomial: 0x864CFB
Initial: 0xB704CE
Reflect input/output: false
Final XOR: 0x000000

Implementation

dart

factory CrcParams.crc24OpenPgp() =>
    CrcParams.hex('0x864cfb', '0xb704ce', false, false, '0x000000');

CrcParams.crc32() factory

factory CrcParams.crc32()

Default CRC-32 parameters.

Alias for CrcParams.crc32IsoHdlc.

Implementation

dart

factory CrcParams.crc32() => CrcParams.crc32IsoHdlc();

CrcParams.crc32IsoHdlc() factory

factory CrcParams.crc32IsoHdlc()

CRC-32/ISO-HDLC parameters, the most common CRC-32 variant.

This is the CRC used by Ethernet, PKZIP, gzip, PNG, and many other protocols and formats.

Polynomial: 0x04C11DB7
Initial: 0xFFFFFFFF
Reflect input/output: true
Final XOR: 0xFFFFFFFF

Implementation

dart

factory CrcParams.crc32IsoHdlc() =>
    CrcParams.hex('0x04c11db7', '0xffffffff', true, true, '0xffffffff');

CrcParams.hex() factory

factory CrcParams.hex(
  String poly,
  String initial,
  bool reflectInput,
  bool reflectOutput,
  String finalXor,
)

Creates CrcParams by parsing poly, initial, and finalXor as hexadecimal strings.

The hex strings must encode the same number of bits. The CRC width is inferred from the hex string length.

dart

// CRC-32 ISO-HDLC
final params = CrcParams.hex(
  '0x04c11db7', '0xffffffff', true, true, '0xffffffff',
);

Implementation

dart

factory CrcParams.hex(
  String poly,
  String initial,
  bool reflectInput,
  bool reflectOutput,
  String finalXor,
) {
  final polyBits = _hex(poly);
  final initialBits = _hex(initial);
  final finalXorBits = _hex(finalXor);

  assert(polyBits.nonEmpty, 'empty polynomial');

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

  return CrcParams(
    polyBits,
    initialBits,
    reflectInput,
    reflectOutput,
    finalXorBits,
  );
}

Properties

finalXor final

final BitVector finalXor

A bitmask XORed with the (possibly reflected) CRC register to produce the final checksum value.

Implementation

dart

final BitVector finalXor;

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

dart

external int get hashCode;

initial final

final BitVector initial

The initial value loaded into the CRC register before processing any input data.

Common values are all-zeros (0x00…) and all-ones (0xFF…).

Implementation

dart

final BitVector initial;

poly final

final BitVector poly

The generator polynomial that defines the CRC algorithm.

The BitVector.size of this value determines the width of the CRC in bits (e.g. 8, 16, 32).

Implementation

dart

final BitVector poly;

reflectInput final

final bool reflectInput

Whether each input byte is bit-reflected (LSB-first) before being fed into the CRC register.

Many hardware CRC implementations process bits LSB-first, requiring this flag to be true for compatibility.

Implementation

dart

final bool reflectInput;

reflectOutput final

final bool reflectOutput

Whether the final CRC register value is bit-reflected before the finalXor is applied.

Implementation

dart

final bool reflectOutput;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

dart

external Type get runtimeType;

width no setter

int get width

The width of this CRC in bits, equal to the size of the polynomial.

Implementation

dart

int get width => poly.size;

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:

dart

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:

dart

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

dart

@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

dart

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

dart

external bool operator ==(Object other);

CrcParams ​

Constructors ​

CrcParams() const ​

CrcParams.crc8() factory ​

CrcParams.crc8Rohc() factory ​

CrcParams.crc8SMBus() factory ​

CrcParams.crc16() factory ​

CrcParams.crc16Arc() factory ​

CrcParams.crc16Kermit() factory ​

CrcParams.crc24() factory ​

CrcParams.crc24OpenPgp() factory ​

CrcParams.crc32() factory ​

CrcParams.crc32IsoHdlc() factory ​

CrcParams.hex() factory ​

Properties ​

finalXor final ​

hashCode no setter inherited ​

initial final ​

poly final ​

reflectInput final ​

reflectOutput final ​

runtimeType no setter inherited ​

width no setter ​

Methods ​

noSuchMethod() inherited ​

toString() inherited ​

Operators ​

operator ==() inherited ​

CrcParams

Constructors

CrcParams() const

CrcParams.crc8() factory

CrcParams.crc8Rohc() factory

CrcParams.crc8SMBus() factory

CrcParams.crc16() factory

CrcParams.crc16Arc() factory

CrcParams.crc16Kermit() factory

CrcParams.crc24() factory

CrcParams.crc24OpenPgp() factory

CrcParams.crc32() factory

CrcParams.crc32IsoHdlc() factory

CrcParams.hex() factory

Properties

finalXor final

hashCode no setter inherited

initial final

poly final

reflectInput final

reflectOutput final

runtimeType no setter inherited

width no setter

Methods

noSuchMethod() inherited

toString() inherited

Operators

operator ==() inherited