1 files changed, 52 insertions, 53 deletions

diff --git a/plumbing/format/idxfile/idxfile.go b/plumbing/format/idxfile/idxfile.go
index 5fed278..14b5860 100644
--- a/plumbing/format/idxfile/idxfile.go
+++ b/plumbing/format/idxfile/idxfile.go
@@ -5,8 +5,9 @@ import (
 	"io"
 	"sort"
 
+	encbin "encoding/binary"
+
 	"gopkg.in/src-d/go-git.v4/plumbing"
-	"gopkg.in/src-d/go-git.v4/utils/binary"
 )
 
 const (
@@ -55,7 +56,8 @@ type MemoryIndex struct {
 	PackfileChecksum [20]byte
 	IdxChecksum      [20]byte
 
-	offsetHash map[int64]plumbing.Hash
+	offsetHash       map[int64]plumbing.Hash
+	offsetHashIsFull bool
 }
 
 var _ Index = (*MemoryIndex)(nil)
@@ -121,31 +123,32 @@ func (idx *MemoryIndex) FindOffset(h plumbing.Hash) (int64, error) {
 		return 0, plumbing.ErrObjectNotFound
 	}
 
-	return idx.getOffset(k, i)
+	offset := idx.getOffset(k, i)
+
+	if !idx.offsetHashIsFull {
+		// Save the offset for reverse lookup
+		if idx.offsetHash == nil {
+			idx.offsetHash = make(map[int64]plumbing.Hash)
+		}
+		idx.offsetHash[int64(offset)] = h
+	}
+
+	return int64(offset), nil
 }
 
 const isO64Mask = uint64(1) << 31
 
-func (idx *MemoryIndex) getOffset(firstLevel, secondLevel int) (int64, error) {
+func (idx *MemoryIndex) getOffset(firstLevel, secondLevel int) uint64 {
 	offset := secondLevel << 2
-	buf := bytes.NewBuffer(idx.Offset32[firstLevel][offset : offset+4])
-	ofs, err := binary.ReadUint32(buf)
-	if err != nil {
-		return -1, err
-	}
+	ofs := encbin.BigEndian.Uint32(idx.Offset32[firstLevel][offset : offset+4])
 
 	if (uint64(ofs) & isO64Mask) != 0 {
 		offset := 8 * (uint64(ofs) & ^isO64Mask)
-		buf := bytes.NewBuffer(idx.Offset64[offset : offset+8])
-		n, err := binary.ReadUint64(buf)
-		if err != nil {
-			return -1, err
-		}
-
-		return int64(n), nil
+		n := encbin.BigEndian.Uint64(idx.Offset64[offset : offset+8])
+		return n
 	}
 
-	return int64(ofs), nil
+	return uint64(ofs)
 }
 
 // FindCRC32 implements the Index interface.
@@ -156,25 +159,34 @@ func (idx *MemoryIndex) FindCRC32(h plumbing.Hash) (uint32, error) {
 		return 0, plumbing.ErrObjectNotFound
 	}
 
-	return idx.getCRC32(k, i)
+	return idx.getCRC32(k, i), nil
 }
 
-func (idx *MemoryIndex) getCRC32(firstLevel, secondLevel int) (uint32, error) {
+func (idx *MemoryIndex) getCRC32(firstLevel, secondLevel int) uint32 {
 	offset := secondLevel << 2
-	buf := bytes.NewBuffer(idx.CRC32[firstLevel][offset : offset+4])
-	return binary.ReadUint32(buf)
+	return encbin.BigEndian.Uint32(idx.CRC32[firstLevel][offset : offset+4])
 }
 
 // FindHash implements the Index interface.
 func (idx *MemoryIndex) FindHash(o int64) (plumbing.Hash, error) {
+	var hash plumbing.Hash
+	var ok bool
+
+	if idx.offsetHash != nil {
+		if hash, ok = idx.offsetHash[o]; ok {
+			return hash, nil
+		}
+	}
+
 	// Lazily generate the reverse offset/hash map if required.
-	if idx.offsetHash == nil {
+	if !idx.offsetHashIsFull || idx.offsetHash == nil {
 		if err := idx.genOffsetHash(); err != nil {
 			return plumbing.ZeroHash, err
 		}
+
+		hash, ok = idx.offsetHash[o]
 	}
 
-	hash, ok := idx.offsetHash[o]
 	if !ok {
 		return plumbing.ZeroHash, plumbing.ErrObjectNotFound
 	}
@@ -190,23 +202,21 @@ func (idx *MemoryIndex) genOffsetHash() error {
 	}
 
 	idx.offsetHash = make(map[int64]plumbing.Hash, count)
-
-	iter, err := idx.Entries()
-	if err != nil {
-		return err
-	}
-
-	for {
-		entry, err := iter.Next()
-		if err != nil {
-			if err == io.EOF {
-				return nil
-			}
-			return err
+	idx.offsetHashIsFull = true
+
+	var hash plumbing.Hash
+	i := uint32(0)
+	for firstLevel, fanoutValue := range idx.Fanout {
+		mappedFirstLevel := idx.FanoutMapping[firstLevel]
+		for secondLevel := uint32(0); i < fanoutValue; i++ {
+			copy(hash[:], idx.Names[mappedFirstLevel][secondLevel*objectIDLength:])
+			offset := int64(idx.getOffset(mappedFirstLevel, int(secondLevel)))
+			idx.offsetHash[offset] = hash
+			secondLevel++
 		}
-
-		idx.offsetHash[int64(entry.Offset)] = entry.Hash
 	}
+
+	return nil
 }
 
 // Count implements the Index interface.
@@ -275,22 +285,11 @@ func (i *idxfileEntryIter) Next() (*Entry, error) {
 			continue
 		}
 
+		mappedFirstLevel := i.idx.FanoutMapping[i.firstLevel]
 		entry := new(Entry)
-		ofs := i.secondLevel * objectIDLength
-		copy(entry.Hash[:], i.idx.Names[i.idx.FanoutMapping[i.firstLevel]][ofs:])
-
-		pos := i.idx.FanoutMapping[entry.Hash[0]]
-
-		offset, err := i.idx.getOffset(pos, i.secondLevel)
-		if err != nil {
-			return nil, err
-		}
-		entry.Offset = uint64(offset)
-
-		entry.CRC32, err = i.idx.getCRC32(pos, i.secondLevel)
-		if err != nil {
-			return nil, err
-		}
+		copy(entry.Hash[:], i.idx.Names[mappedFirstLevel][i.secondLevel*objectIDLength:])
+		entry.Offset = i.idx.getOffset(mappedFirstLevel, i.secondLevel)
+		entry.CRC32 = i.idx.getCRC32(mappedFirstLevel, i.secondLevel)
 
 		i.secondLevel++
 		i.total++