snapshot of https://github.com/seaweedfs/seaweedfs.git (master, 2026-09-16; blobs > 131072B omitted)

weed/storage/erasure_coding/ec_locate.go

@@ -0,0 +1,98 @@
+package erasure_coding
+
+import (
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+)
+
+type Interval struct {
+	BlockIndex          int // the index of the block in either the large blocks or the small blocks
+	InnerBlockOffset    int64
+	Size                types.Size
+	IsLargeBlock        bool // whether the block is a large block or a small block
+	LargeBlockRowsCount int
+}
+
+// LocateData finds the intervals of data within erasure coding blocks for a given offset and size.
+func LocateData(largeBlockLength, smallBlockLength int64, shardDatSize int64, offset int64, size types.Size) (intervals []Interval) {
+	blockIndex, isLargeBlock, nLargeBlockRows, innerBlockOffset := locateOffset(largeBlockLength, smallBlockLength, shardDatSize, offset)
+
+	for size > 0 {
+		blockRemaining := largeBlockLength - innerBlockOffset
+		if !isLargeBlock {
+			blockRemaining = smallBlockLength - innerBlockOffset
+		}
+
+		if blockRemaining <= 0 {
+			// move to next block
+			blockIndex, isLargeBlock = moveToNextBlock(blockIndex, isLargeBlock, nLargeBlockRows)
+			innerBlockOffset = 0
+			continue
+		}
+
+		interval := Interval{
+			BlockIndex:          blockIndex,
+			InnerBlockOffset:    innerBlockOffset,
+			IsLargeBlock:        isLargeBlock,
+			LargeBlockRowsCount: int(nLargeBlockRows),
+		}
+
+		if int64(size) <= blockRemaining {
+			interval.Size = size
+			intervals = append(intervals, interval)
+			return
+		}
+		interval.Size = types.Size(blockRemaining)
+		intervals = append(intervals, interval)
+
+		size -= interval.Size
+		blockIndex, isLargeBlock = moveToNextBlock(blockIndex, isLargeBlock, nLargeBlockRows)
+		innerBlockOffset = 0
+
+	}
+	return
+}
+
+func moveToNextBlock(blockIndex int, isLargeBlock bool, nLargeBlockRows int64) (int, bool) {
+	nextBlockIndex := blockIndex + 1
+	nextIsLargeBlock := isLargeBlock
+	if isLargeBlock && int64(nextBlockIndex) == nLargeBlockRows*DataShardsCount {
+		nextIsLargeBlock = false
+		nextBlockIndex = 0
+	}
+	return nextBlockIndex, nextIsLargeBlock
+}
+
+func locateOffset(largeBlockLength, smallBlockLength int64, shardDatSize int64, offset int64) (blockIndex int, isLargeBlock bool, nLargeBlockRows int64, innerBlockOffset int64) {
+	largeRowSize := largeBlockLength * DataShardsCount
+	nLargeBlockRows = shardDatSize / largeBlockLength
+
+	// if offset is within the large block area
+	if offset < nLargeBlockRows*largeRowSize {
+		isLargeBlock = true
+		blockIndex, innerBlockOffset = locateOffsetWithinBlocks(largeBlockLength, offset)
+		return
+	}
+
+	isLargeBlock = false
+	offset -= nLargeBlockRows * largeRowSize
+	blockIndex, innerBlockOffset = locateOffsetWithinBlocks(smallBlockLength, offset)
+	return
+}
+
+func locateOffsetWithinBlocks(blockLength int64, offset int64) (blockIndex int, innerBlockOffset int64) {
+	blockIndex = int(offset / blockLength)
+	innerBlockOffset = offset % blockLength
+	return
+}
+
+func (interval Interval) ToShardIdAndOffset(largeBlockSize, smallBlockSize int64) (ShardId, int64) {
+	ecFileOffset := interval.InnerBlockOffset
+	rowIndex := interval.BlockIndex / DataShardsCount
+	if interval.IsLargeBlock {
+		ecFileOffset += int64(rowIndex) * largeBlockSize
+	} else {
+		ecFileOffset += int64(interval.LargeBlockRowsCount)*largeBlockSize + int64(rowIndex)*smallBlockSize
+	}
+	ecFileIndex := interval.BlockIndex % DataShardsCount
+	return ShardId(ecFileIndex), ecFileOffset
+}