func()

in cpc/cpc_compressed_state.go [278:338]
42 lines of code
9 McCabe index (conditional complexity)

func (c *CpcCompressedState) uncompressHybridFlavor(src *CpcSketch) error {
	// Ensure that the window compression stream is nil and the CSV stream is present.
	if c.CwStream != nil {
		return fmt.Errorf("uncompressHybridFlavor: expected CwStream to be nil, got %v", c.CwStream)
	}
	if c.CsvStream == nil {
		return fmt.Errorf("uncompressHybridFlavor: CsvStream is nil")
	}

	// Uncompress the surprising values (i.e. the pairs) from the CSV stream.
	pairs, err := uncompressTheSurprisingValues(c)
	if err != nil {
		return err
	}
	numPairs := int(c.NumCsv)

	// For the hybrid flavor, some pairs belong to the sliding window.
	srcLgK := c.LgK
	k := 1 << srcLgK

	// Allocate a window of k bytes (one byte per row).
	window := make([]byte, k)

	// Separate out the pairs that belong in the window.
	// Pairs with a column index (low 6 bits) less than 8 are moved into the window.
	nextTruePair := 0
	for i := 0; i < numPairs; i++ {
		rowCol := pairs[i]
		if rowCol == -1 {
			return fmt.Errorf("uncompressHybridFlavor: invalid pair value -1 at index %d", i)
		}
		col := rowCol & 63
		if col < 8 {
			row := rowCol >> 6
			window[row] |= 1 << col // set the corresponding bit in the window
		} else {
			// Move the "true" pair down into the pairs array.
			pairs[nextTruePair] = rowCol
			nextTruePair++
		}
	}

	// The compressed state's window offset should be 0.
	if c.getWindowOffset() != 0 {
		return fmt.Errorf("uncompressHybridFlavor: expected windowOffset to be 0, got %d", c.getWindowOffset())
	}
	// Set the target sketch's windowOffset to 0.
	src.windowOffset = 0

	// Build a new pair table from the true pairs.
	table, err := newInstanceFromPairsArray(pairs, nextTruePair, srcLgK)
	if err != nil {
		return err
	}
	src.pairTable = table

	// Set the sliding window in the target sketch.
	src.slidingWindow = window

	return nil
}