Method PcsaUpdate

be/src/exprs/aggregate-functions-ir.cc:1544–1562

template<typename T>
void AggregateFunctions::PcsaUpdate(FunctionContext* c, const T& input, StringVal* dst) {
  DCHECK_EQ(dst->len, PC_INTERMEDIATE_BYTES);
  if (input.is_null) return;

  // Core of the algorithm. This is a direct translation of the code in the paper.
  // Please see the paper for details. Using stochastic averaging, we only need to
  // the hash value once for each row.
  uint32_t hash_value = AnyValUtil::Hash(input, *c->GetArgType(0), 0);
  uint32_t row_index = hash_value % NUM_PC_BITMAPS;

  // We want the zero-based position of the least significant 1-bit in binary
  // representation of hash_value. BitUtil::CountTrailingZeros(x,y) does exactly this
  // because it returns the number of trailing 0-bits in x (or y if x is zero).
  const int bit_index =
      BitUtil::CountTrailingZeros(hash_value / NUM_PC_BITMAPS, PC_BITMAP_LENGTH - 1);

  // Set bitmap[row_index, bit_index] to 1
  SetDistinctEstimateBit(dst->ptr, row_index, bit_index);
}

string DistinctEstimateBitMapToString(uint8_t* v) {
  stringstream debugstr;