wp

storage/navigation.go

@@ -0,0 +1,214 @@
+package storage
+
+import bin "gordenko.dev/dima/bin/little"
+
+const (
+	PageNoSize = 4
+)
+
+type KeyComparator interface {
+	CompareTo(int) int
+}
+
+type ValueAtComparator struct {
+	buf       []byte
+	timestamp uint32
+}
+
+func (s ValueAtComparator) CompareTo(elemIdx int) int {
+	var (
+		pos     = elemIdx * IndexRecordSize
+		elem, _ = bin.GetUint32(s.buf[pos:])
+	)
+
+	if s.timestamp < elem {
+		return -1
+	} else if s.timestamp > elem {
+		return 1
+	} else {
+		return 0
+	}
+}
+
+func BinarySearch(qty int, keyComparator KeyComparator) (elemIdx int, isFound bool) {
+	if qty == 0 {
+		return
+	}
+	a := 0
+	b := qty - 1
+	for {
+		var (
+			elemIdx = (b-a)/2 + a
+			code    = keyComparator.CompareTo(elemIdx)
+		)
+		if code == 1 {
+			a = elemIdx + 1
+			if a > b {
+				return elemIdx, false // +1
+			}
+		} else if code == -1 {
+			b = elemIdx - 1
+			if b < a {
+				if elemIdx == 0 {
+					return 0, false
+				} else {
+					return elemIdx - 1, false
+				}
+			}
+		} else {
+			return elemIdx, true
+		}
+	}
+}
+
+// func getPrevPageNo(buf []byte) uint32 {
+// 	pageNo, _ := bin.GetUint32(buf[prevPageIdx:])
+// 	return pageNo
+// }
+
+// func GetIndexRecordsSince(buf []byte) (pageNo uint32) {
+// 	pageNo, _ = bin.GetUint32(buf)
+// 	return
+// }
+
+func FindPageOnIndexLevelTail(level IndexLevelTail, timestamp uint32) (pageNo uint32) {
+	comparator := ValueAtComparator{
+		buf:       level.Buffer,
+		timestamp: timestamp,
+	}
+	elemIdx, _ := BinarySearch(level.RecordsCount, comparator)
+	pos := elemIdx*IndexRecordSize + 4 // timestamp size
+	pageNo, _ = bin.GetUint32(level.Buffer[pos:])
+	return
+}
+
+// func FindPageOnRecords(records []byte, timestamp uint32) (pageNo uint32) {
+// 	comparator := ValueAtComparator{
+// 		buf:       records,
+// 		timestamp: timestamp,
+// 	}
+// 	count := len(records) / IndexRecordSize
+// 	elemIdx, _ := BinarySearch(count, comparator)
+// 	pageNo, _ = bin.GetUint32(records[elemIdx*IndexRecordSize:])
+// 	return
+// }
+
+func FindPageOnIndexPage(page []byte, timestamp uint32) (pageNo uint32) {
+	comparator := ValueAtComparator{
+		buf:       page,
+		timestamp: timestamp,
+	}
+	count, _ := bin.GetUint16(page[indexRecordsCountIdx:])
+	elemIdx, _ := BinarySearch(int(count), comparator)
+	pos := elemIdx*IndexRecordSize + 4 // timestamp size
+	pageNo, _ = bin.GetUint32(page[pos:])
+	return
+}
+
+func IsZeroLevelPage(buf []byte) bool {
+	return buf[isZeroLevelIdx] == 1
+}
+
+// можна перевірити хвости від 0 до ... Перевіряю since кожного хвоста.
+// Якщо timestamp >=, шукаю pageNo бінарним пошуком. І сторінка мені однозначно підходить.
+// Якщо timestamp <, піднімаюсь вище. Якщо рівнів більше немає - until вказано за межами Range показань.
+func FindPageOnIndexLevelTails(levels []IndexLevelTail, timestamp uint32) (pageNo uint32, isDataPage bool) {
+	for i, level := range levels {
+		tailSince, _ := bin.GetUint32(level.Buffer)
+		if timestamp >= tailSince {
+			pageNo = FindPageOnIndexLevelTail(level, timestamp)
+			return pageNo, i == 0
+		}
+	}
+	return
+}
+
+// func findPageNoIdx(buf []byte, timestamp uint32) (idx int) {
+// 	comparator := ValueAtComparator{
+// 		buf:       buf,
+// 		timestamp: timestamp,
+// 	}
+// 	qty, _ := bin.GetUint16(buf[indexRecordsQtyIdx:])
+// 	elemIdx, _ := BinarySearch(int(qty), comparator)
+// 	return elemIdx
+// }
+
+// func findPageNoForDeleteSince(buf []byte, since uint32) (uint32, int, int) {
+// 	comparator := ValueAtComparator{
+// 		buf:       buf,
+// 		timestamp: since,
+// 	}
+// 	qty, _ := bin.GetUint16(buf[indexRecordsQtyIdx:])
+// 	elemIdx, _ := BinarySearch(int(qty), comparator)
+// 	pos := elemIdx * timestampSize
+// 	timestamp, _ := bin.GetUint32(buf[pos:])
+
+// 	if timestamp == since {
+// 		if elemIdx == 0 {
+// 			return 0, int(qty), -1
+// 		}
+// 		elemIdx--
+// 	}
+// 	pos = indexFooterIdx - (elemIdx+1)*PageNoSize
+// 	pageNo, _ := bin.GetUint32(buf[pos:])
+// 	return pageNo, int(qty), elemIdx
+// }
+
+// func getLastPageNo(buf []byte) (pageNo uint32) {
+// 	qty, _ := bin.GetUint16(buf[indexRecordsQtyIdx:])
+// 	pos := indexFooterIdx - qty*PageNoSize
+// 	pageNo, _ = bin.GetUint32(buf[pos:])
+// 	return
+// }
+
+// func getPageNo(buf []byte, idx int) (pageNo uint32) {
+// 	pos := indexFooterIdx - (idx+1)*PageNoSize
+// 	pageNo, _ = bin.GetUint32(buf[pos:])
+// 	return
+// }
+
+// func listPageNumbers(buf []byte) (pageNumbers []uint32) {
+// 	qty, _ := bin.GetUint16(buf[indexRecordsQtyIdx:])
+// 	pos := indexFooterIdx - PageNoSize
+// 	for range qty {
+// 		pageNo, _ := bin.GetUint32(buf[pos:])
+// 		pageNumbers = append(pageNumbers, pageNo)
+// 		pos -= PageNoSize
+// 	}
+// 	return
+// }
+
+// // include since timestamp
+// func listPageNumbersSince(buf []byte, timestamp uint32) (pageNumbers []uint32) {
+// 	comparator := ValueAtComparator{
+// 		buf:       buf,
+// 		timestamp: timestamp,
+// 	}
+// 	qty, _ := bin.GetUint16(buf[indexRecordsQtyIdx:])
+// 	elemIdx, _ := BinarySearch(int(qty), comparator)
+// 	pos := indexFooterIdx - (elemIdx+1)*PageNoSize
+// 	for range qty {
+// 		pageNo, _ := bin.GetUint32(buf[pos:])
+// 		pageNumbers = append(pageNumbers, pageNo)
+// 		pos -= PageNoSize
+// 	}
+// 	return
+// }
+
+// func getSince(buf []byte) uint32 {
+// 	return bin.GetUint32(buf[0:])
+// }
+
+// func appendPair(buf []byte, timestamp uint32, pageNo uint32) bool {
+// 	qty := bin.GetUint16AsInt(buf[indexRecordsQtyIdx:])
+// 	free := indexFooterIdx - qty*pairSize
+// 	if free < pairSize {
+// 		return false
+// 	}
+// 	pos := qty * timestampSize
+// 	bin.PutUint32(buf[pos:], timestamp)
+// 	pos = indexFooterIdx - (qty+1)*PageNoSize
+// 	bin.PutUint32(buf[pos:], pageNo)
+// 	bin.PutIntAsUint16(buf[indexRecordsQtyIdx:], qty+1)
+// 	return true
+// }