FixedPointSqrt constructor

Implementation

FixedPointSqrt(super.a) {
  if (a.signed) {
    throw RohdHclException('Signed values not supported');
  }

  Logic solution = FixedPoint(
      signed: a.signed,
      name: 'solution',
      integerWidth: a.integerWidth + 1,
      fractionWidth: a.fractionWidth + 1);
  Logic remainder = FixedPoint(
      signed: a.signed,
      name: 'remainder',
      integerWidth: a.integerWidth + 1,
      fractionWidth: a.fractionWidth + 1);
  Logic subtractionValue = FixedPoint(
      signed: a.signed,
      name: 'subValue',
      integerWidth: a.integerWidth + 1,
      fractionWidth: a.fractionWidth + 1);
  Logic aLoc = FixedPoint(
      signed: a.signed,
      name: 'aLoc',
      integerWidth: a.integerWidth + 1,
      fractionWidth: a.fractionWidth + 1);

  solution = Const(0, width: aLoc.width).named('solution');
  remainder = Const(0, width: aLoc.width).named('remainder');
  subtractionValue = Const(0, width: aLoc.width).named('subtraction');
  aLoc = [Const(0), a, Const(0)].swizzle().named('a_loc');

  final outputSqrt = a.clone(name: 'sqrt');
  output('sqrt') <= outputSqrt;

  // loop once through input value
  for (var i = 0; i < ((width + 2) >> 1); i++) {
    // append bits from a, two at a time
    remainder = [
      remainder.slice(width + 2 - 3, 0),
      aLoc.slice(aLoc.width - 1 - (i * 2), aLoc.width - 2 - (i * 2))
    ].swizzle().named('remainder_iter$i');
    subtractionValue = [solution.slice(width + 2 - 3, 0), Const(1, width: 2)]
        .swizzle()
        .named('subtraction_value_iter$i');
    solution = [
      solution.slice(width + 2 - 2, 0),
      subtractionValue.lte(remainder)
    ].swizzle().named('solution_iter$i');
    remainder = mux(subtractionValue.lte(remainder),
            remainder - subtractionValue, remainder)
        .named('remainder_mux_iter$i');
  }

  // loop again to finish remainder
  for (var i = 0; i < ((width + 2) >> 1) - 1; i++) {
    // don't try to append bits from a, they are done
    remainder = [remainder.slice(width + 2 - 3, 0), Const(0, width: 2)]
        .swizzle()
        .named('remainder_final_iter$i');
    subtractionValue = [solution.slice(width + 2 - 3, 0), Const(1, width: 2)]
        .swizzle()
        .named('subtraction_value_final_iter$i');
    solution = [
      solution.slice(width + 2 - 2, 0),
      subtractionValue.lte(remainder)
    ].swizzle().named('solution_final_iter$i');
    remainder = mux(subtractionValue.lte(remainder),
            remainder - subtractionValue, remainder)
        .named('remainder_finalmux_iter$i');
  }
  solution = (solution + 1).named('solutionPlusOne');
  outputSqrt <=
      solution.slice(aLoc.width - 1, aLoc.width - a.width).named('solutionF');
}