func()

in cpc/cpc_compressed_state.go [463:526]
48 lines of code
11 McCabe index (conditional complexity)

func (c *CpcCompressedState) uncompressSlidingFlavor(src *CpcSketch) error {
	// Ensure that cwStream is not nil.
	if c.CwStream == nil {
		return fmt.Errorf("uncompressSlidingFlavor: expected cwStream to be non-nil")
	}
	// Uncompress the window portion.
	if err := uncompressTheWindow(src, c); err != nil {
		return err
	}

	srcLgK := c.LgK
	numPairs := int(c.NumCsv)
	if numPairs == 0 {
		// Create an empty pair table.
		pt, err := NewPairTable(2, 6+srcLgK)
		if err != nil {
			return err
		}
		src.pairTable = pt
	} else {
		// Ensure csvStream is present.
		if c.CsvStream == nil {
			return fmt.Errorf("uncompressSlidingFlavor: expected csvStream to be non-nil")
		}
		// Uncompress the surprising values.
		pairs, err := uncompressTheSurprisingValues(c)
		if err != nil {
			return err
		}

		// Determine pseudoPhase.
		pseudoPhase := determinePseudoPhase(srcLgK, int64(c.NumCoupons))
		if pseudoPhase >= 16 {
			return fmt.Errorf("uncompressSlidingFlavor: pseudoPhase %d out of range", pseudoPhase)
		}
		permutation := columnPermutationsForDecoding[pseudoPhase]

		// Get the window offset; it must be in (0, 56].
		offset := c.getWindowOffset()
		if offset <= 0 || offset > 56 {
			return fmt.Errorf("uncompressSlidingFlavor: invalid window offset %d", offset)
		}

		// For each pair, undo the permutation and rotation.
		for i := 0; i < numPairs; i++ {
			rowCol := pairs[i]
			row := rowCol >> 6
			col := rowCol & 63
			// First, undo the permutation.
			col = int(permutation[col])
			// Then, undo the rotation: old = (new + (offset+8)) mod 64.
			col = (col + (offset + 8)) & 63
			pairs[i] = (row << 6) | col
		}

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