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package pack
import (
"encoding/binary"
"hash"
)
// V1 implements IndexVersion for v1 packfiles.
type V1 struct {
hash hash.Hash
}
// Name implements IndexVersion.Name by returning the 20 byte SHA-1 object name
// for the given entry at offset "at" in the v1 index file "idx".
func (v *V1) Name(idx *Index, at int64) ([]byte, error) {
var sha [MaxHashSize]byte
hashlen := v.hash.Size()
if _, err := idx.readAt(sha[:hashlen], v1ShaOffset(at, int64(hashlen))); err != nil {
return nil, err
}
return sha[:hashlen], nil
}
// Entry implements IndexVersion.Entry for v1 packfiles by parsing and returning
// the IndexEntry specified at the offset "at" in the given index file.
func (v *V1) Entry(idx *Index, at int64) (*IndexEntry, error) {
var offs [4]byte
if _, err := idx.readAt(offs[:], v1EntryOffset(at, int64(v.hash.Size()))); err != nil {
return nil, err
}
return &IndexEntry{
PackOffset: uint64(binary.BigEndian.Uint32(offs[:])),
}, nil
}
// Width implements IndexVersion.Width() by returning the number of bytes that
// v1 packfile index header occupy.
func (v *V1) Width() int64 {
return indexV1Width
}
// v1ShaOffset returns the location of the SHA1 of an object given at "at".
func v1ShaOffset(at int64, hashlen int64) int64 {
// Skip forward until the desired entry.
return v1EntryOffset(at, hashlen) +
// Skip past the 4-byte object offset in the desired entry to
// the SHA1.
indexObjectSmallOffsetWidth
}
// v1EntryOffset returns the location of the packfile offset for the object
// given at "at".
func v1EntryOffset(at int64, hashlen int64) int64 {
// Skip the L1 fanout table
return indexOffsetV1Start +
// Skip the object entries before the one located at "at"
((hashlen + indexObjectSmallOffsetWidth) * at)
}
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