Add transition table compressor

2 files changed, 336 insertions, 0 deletions

diff --git a/compressor/compressor.go b/compressor/compressor.go
new file mode 100644
index 0000000..cdfeacb
--- /dev/null
+++ b/compressor/compressor.go
@@ -0,0 +1,214 @@
+package compressor
+
+import (
+	"encoding/binary"
+	"fmt"
+	"sort"
+)
+
+type OriginalTable struct {
+	entries  []int
+	rowCount int
+	colCount int
+}
+
+func NewOriginalTable(entries []int, colCount int) (*OriginalTable, error) {
+	if len(entries) == 0 {
+		return nil, fmt.Errorf("enries is empty")
+	}
+	if colCount <= 0 {
+		return nil, fmt.Errorf("colCount must be >=1")
+	}
+	if len(entries)%colCount != 0 {
+		return nil, fmt.Errorf("entries length or column count are incorrect; entries length: %v, column count: %v", len(entries), colCount)
+	}
+
+	return &OriginalTable{
+		entries:  entries,
+		rowCount: len(entries) / colCount,
+		colCount: colCount,
+	}, nil
+}
+
+type Compressor interface {
+	Compress(orig *OriginalTable) error
+	Lookup(row, col int) (int, error)
+	OriginalTableSize() (int, int)
+}
+
+var (
+	_ Compressor = &UniqueEntriesTable{}
+	_ Compressor = &RowDisplacementTable{}
+)
+
+type UniqueEntriesTable struct {
+	UniqueEntries    []int
+	RowNums          []int
+	OriginalRowCount int
+	OriginalColCount int
+}
+
+func NewUniqueEntriesTable() *UniqueEntriesTable {
+	return &UniqueEntriesTable{}
+}
+
+func (tab *UniqueEntriesTable) Lookup(row, col int) (int, error) {
+	if row < 0 || row >= tab.OriginalRowCount || col < 0 || col >= tab.OriginalColCount {
+		return 0, fmt.Errorf("indexes are out of range: [%v, %v]", row, col)
+	}
+	return tab.UniqueEntries[tab.RowNums[row]*tab.OriginalColCount+col], nil
+}
+
+func (tab *UniqueEntriesTable) OriginalTableSize() (int, int) {
+	return tab.OriginalRowCount, tab.OriginalColCount
+}
+
+func (tab *UniqueEntriesTable) Compress(orig *OriginalTable) error {
+	var uniqueEntries []int
+	rowNums := make([]int, orig.rowCount)
+	hash2RowNum := map[string]int{}
+	nextRowNum := 0
+	for row := 0; row < orig.rowCount; row++ {
+		var rowHash string
+		{
+			buf := make([]byte, 0, orig.colCount*8)
+			for col := 0; col < orig.colCount; col++ {
+				b := make([]byte, 8)
+				binary.PutUvarint(b, uint64(orig.entries[row*orig.colCount+col]))
+				buf = append(buf, b...)
+			}
+			rowHash = string(buf)
+		}
+		rowNum, ok := hash2RowNum[rowHash]
+		if !ok {
+			rowNum = nextRowNum
+			nextRowNum++
+			hash2RowNum[rowHash] = rowNum
+			start := row * orig.colCount
+			entry := append([]int{}, orig.entries[start:start+orig.colCount]...)
+			uniqueEntries = append(uniqueEntries, entry...)
+		}
+		rowNums[row] = rowNum
+	}
+
+	tab.UniqueEntries = uniqueEntries
+	tab.RowNums = rowNums
+	tab.OriginalRowCount = orig.rowCount
+	tab.OriginalColCount = orig.colCount
+
+	return nil
+}
+
+const ForbiddenValue = -1
+
+type RowDisplacementTable struct {
+	OriginalRowCount int
+	OriginalColCount int
+	EmptyValue       int
+	Entries          []int
+	Bounds           []int
+	RowDisplacement  []int
+}
+
+func NewRowDisplacementTable(emptyValue int) *RowDisplacementTable {
+	return &RowDisplacementTable{
+		EmptyValue: emptyValue,
+	}
+}
+
+func (tab *RowDisplacementTable) Lookup(row int, col int) (int, error) {
+	if row < 0 || row >= tab.OriginalRowCount || col < 0 || col >= tab.OriginalColCount {
+		return tab.EmptyValue, fmt.Errorf("indexes are out of range: [%v, %v]", row, col)
+	}
+	d := tab.RowDisplacement[row]
+	if tab.Bounds[d+col] != row {
+		return tab.EmptyValue, nil
+	}
+	return tab.Entries[d+col], nil
+}
+
+func (tab *RowDisplacementTable) OriginalTableSize() (int, int) {
+	return tab.OriginalRowCount, tab.OriginalColCount
+}
+
+type rowInfo struct {
+	rowNum        int
+	nonEmptyCount int
+	nonEmptyCol   []int
+}
+
+func (tab *RowDisplacementTable) Compress(orig *OriginalTable) error {
+	rowInfo := make([]rowInfo, orig.rowCount)
+	{
+		row := 0
+		col := 0
+		rowInfo[0].rowNum = 0
+		for _, v := range orig.entries {
+			if col == orig.colCount {
+				row++
+				col = 0
+				rowInfo[row].rowNum = row
+			}
+			if v != tab.EmptyValue {
+				rowInfo[row].nonEmptyCount++
+				rowInfo[row].nonEmptyCol = append(rowInfo[row].nonEmptyCol, col)
+			}
+			col++
+		}
+
+		sort.SliceStable(rowInfo, func(i int, j int) bool {
+			return rowInfo[i].nonEmptyCount > rowInfo[j].nonEmptyCount
+		})
+	}
+
+	origEntriesLen := len(orig.entries)
+	entries := make([]int, origEntriesLen)
+	bounds := make([]int, origEntriesLen)
+	resultBottom := orig.colCount
+	rowDisplacement := make([]int, orig.rowCount)
+	{
+		for i := 0; i < origEntriesLen; i++ {
+			entries[i] = tab.EmptyValue
+			bounds[i] = ForbiddenValue
+		}
+
+		nextRowDisplacement := 0
+		for _, rInfo := range rowInfo {
+			if rInfo.nonEmptyCount <= 0 {
+				continue
+			}
+
+			for {
+				isOverlapped := false
+				for _, col := range rInfo.nonEmptyCol {
+					if entries[nextRowDisplacement+col] == tab.EmptyValue {
+						continue
+					}
+					nextRowDisplacement++
+					isOverlapped = true
+					break
+				}
+				if isOverlapped {
+					continue
+				}
+
+				rowDisplacement[rInfo.rowNum] = nextRowDisplacement
+				for _, col := range rInfo.nonEmptyCol {
+					entries[nextRowDisplacement+col] = orig.entries[(rInfo.rowNum*orig.colCount)+col]
+					bounds[nextRowDisplacement+col] = rInfo.rowNum
+				}
+				resultBottom = nextRowDisplacement + orig.colCount
+				nextRowDisplacement++
+				break
+			}
+		}
+	}
+
+	tab.OriginalRowCount = orig.rowCount
+	tab.OriginalColCount = orig.colCount
+	tab.Entries = entries[:resultBottom]
+	tab.Bounds = bounds[:resultBottom]
+	tab.RowDisplacement = rowDisplacement
+
+	return nil
+}
diff --git a/compressor/compressor_test.go b/compressor/compressor_test.go
new file mode 100644
index 0000000..621b731
--- /dev/null
+++ b/compressor/compressor_test.go
@@ -0,0 +1,122 @@
+package compressor
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestCompressor_Compress(t *testing.T) {
+	x := 0 // an empty value
+
+	allCompressors := func() []Compressor {
+		return []Compressor{
+			NewUniqueEntriesTable(),
+			NewRowDisplacementTable(x),
+		}
+	}
+
+	tests := []struct {
+		original    []int
+		rowCount    int
+		colCount    int
+		compressors []Compressor
+	}{
+		{
+			original: []int{
+				1, 1, 1, 1, 1,
+				1, 1, 1, 1, 1,
+				1, 1, 1, 1, 1,
+			},
+			rowCount:    3,
+			colCount:    5,
+			compressors: allCompressors(),
+		},
+		{
+			original: []int{
+				x, x, x, x, x,
+				x, x, x, x, x,
+				x, x, x, x, x,
+			},
+			rowCount:    3,
+			colCount:    5,
+			compressors: allCompressors(),
+		},
+		{
+			original: []int{
+				1, 1, 1, 1, 1,
+				x, x, x, x, x,
+				1, 1, 1, 1, 1,
+			},
+			rowCount:    3,
+			colCount:    5,
+			compressors: allCompressors(),
+		},
+		{
+			original: []int{
+				1, x, 1, 1, 1,
+				1, 1, x, 1, 1,
+				1, 1, 1, x, 1,
+			},
+			rowCount:    3,
+			colCount:    5,
+			compressors: allCompressors(),
+		},
+	}
+	for i, tt := range tests {
+		for _, comp := range tt.compressors {
+			t.Run(fmt.Sprintf("%T #%v", comp, i), func(t *testing.T) {
+				dup := make([]int, len(tt.original))
+				copy(dup, tt.original)
+
+				orig, err := NewOriginalTable(tt.original, tt.colCount)
+				if err != nil {
+					t.Fatal(err)
+				}
+				err = comp.Compress(orig)
+				if err != nil {
+					t.Fatal(err)
+				}
+				rowCount, colCount := comp.OriginalTableSize()
+				if rowCount != tt.rowCount || colCount != tt.colCount {
+					t.Fatalf("unexpected table size; want: %vx%v, got: %vx%v", tt.rowCount, tt.colCount, rowCount, colCount)
+				}
+				for i := 0; i < tt.rowCount; i++ {
+					for j := 0; j < tt.colCount; j++ {
+						v, err := comp.Lookup(i, j)
+						if err != nil {
+							t.Fatal(err)
+						}
+						expected := tt.original[i*tt.colCount+j]
+						if v != expected {
+							t.Fatalf("unexpected entry (%v, %v); want: %v, got: %v", i, j, expected, v)
+						}
+					}
+				}
+
+				// Calling with out-of-range indexes should be an error.
+				if _, err := comp.Lookup(0, -1); err == nil {
+					t.Fatalf("expected error didn't occur (0, -1)")
+				}
+				if _, err := comp.Lookup(-1, 0); err == nil {
+					t.Fatalf("expected error didn't occur (-1, 0)")
+				}
+				if _, err := comp.Lookup(rowCount-1, colCount); err == nil {
+					t.Fatalf("expected error didn't occur (%v, %v)", rowCount-1, colCount)
+				}
+				if _, err := comp.Lookup(rowCount, colCount-1); err == nil {
+					t.Fatalf("expected error didn't occur (%v, %v)", rowCount, colCount-1)
+				}
+
+				// The compressor must not break the original table.
+				for i := 0; i < tt.rowCount; i++ {
+					for j := 0; j < tt.colCount; j++ {
+						idx := i*tt.colCount + j
+						if tt.original[idx] != dup[idx] {
+							t.Fatalf("the original table is broken (%v, %v); want: %v, got: %v", i, j, dup[idx], tt.original[idx])
+						}
+					}
+				}
+			})
+		}
+	}
+}