CarrySelectOnesComplementCompoundAdder constructor

CarrySelectOnesComplementCompoundAdder(
  1. Logic a,
  2. Logic b, {
  3. Adder adderGen(
    1. Logic,
    2. Logic, {
    3. Logic? carryIn,
    }) = NativeAdder.new,
  4. Logic? subtractIn,
  5. bool generateCarryOut = false,
  6. bool generateCarryOutP1 = false,
  7. bool subtract = false,
  8. List<int> widthGen(
    1. int
    ) = CarrySelectCompoundAdder.splitSelectAdderAlgorithmSingleBlock,
  9. String name = 'compound_adder',
  10. bool reserveName = false,
  11. bool reserveDefinitionName = false,
  12. String? definitionName,
})

Constructs a CarrySelectCompoundAdder using a set of OnesComplementAdder in a carry-select configuration. Adds (or subtracts) a and b to produce sum and sumP1 (sum plus 1).

  • adderGen is the adder generator Function inside the OnesComplementAdder.
  • subtractIn is an optional Logic control for subtraction.
  • subtract is a boolean control for subtraction. It must be false(default) if a subtractIn Logic is provided.
  • generateCarryOut set to true will create output carryOut and employ the ones-complement optimization of not adding '1' to convert back to 2s complement during subtraction on the sum.
  • generateCarryOutP1 set to true will create output carryOutP1 and employ the ones-complement optimization of not adding '1' to convert back to 2s complement during subtraction on the sumP1.
  • widthGen is a Function which produces a list for splitting the adder for the carry-select chain. The default is CarrySelectCompoundAdder.splitSelectAdderAlgorithmSingleBlock,

Implementation

CarrySelectOnesComplementCompoundAdder(super.a, super.b,
    {Adder Function(Logic, Logic, {Logic? carryIn}) adderGen =
        NativeAdder.new,
    Logic? subtractIn,
    bool generateCarryOut = false,
    bool generateCarryOutP1 = false,
    bool subtract = false,
    List<int> Function(int) widthGen =
        CarrySelectCompoundAdder.splitSelectAdderAlgorithmSingleBlock,
    super.name,
    super.reserveName,
    super.reserveDefinitionName,
    String? definitionName})
    : super(
          definitionName: definitionName ??
              'CarrySelectOnesComplementCompoundAdder_W${a.width}') {
  subtractIn = (subtractIn != null)
      ? addInput('subtractIn', subtractIn, width: subtractIn.width)
      : null;

  if (generateCarryOut) {
    addOutput('carryOut');
  }
  if (generateCarryOutP1) {
    addOutput('carryOutP1');
  }

  final doSubtract = subtractIn ?? (subtract ? Const(subtract) : Const(0));

  final csadder = CarrySelectCompoundAdder(a, b,
      widthGen: widthGen,
      subtractIn: subtractIn,
      adderGen: (a, b, {carryIn, subtractIn, name = 'ones_complement'}) =>
          OnesComplementAdder(a, b,
              adderGen: adderGen,
              carryIn: carryIn,
              generateEndAroundCarry: true,
              subtract: subtract,
              chainable: true,
              subtractIn: subtractIn));

  addOutput('sign') <= mux(doSubtract, ~csadder.sum[-1], Const(0));
  addOutput('signP1') <= mux(doSubtract, ~csadder.sumP1[-1], Const(0));
  final sumPlus1 =
      mux(doSubtract & csadder.sumP1[-1], ~csadder.sumP1, csadder.sumP1);
  if (generateCarryOutP1) {
    sumP1 <= sumPlus1;
    carryOutP1! <= csadder.sumP1[-1];
  } else {
    sumP1 <=
        mux(csadder.sumP1[-1],
            ParallelPrefixIncr(sumPlus1).out.named('sumPlus2'), sumPlus1);
  }
  if (generateCarryOut) {
    sum <= mux(doSubtract & csadder.sum[-1], ~csadder.sum, csadder.sum);
    carryOut! <= csadder.sum[-1];
  } else {
    sum <= mux(doSubtract & csadder.sum[-1], sumPlus1, csadder.sum);
  }
}