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package packfile
import "io"
const deltaSizeMin = 4
func deltaHeaderSize(b []byte) (uint, []byte) {
var size, j uint
var cmd byte
for {
cmd = b[j]
size |= (uint(cmd) & 0x7f) << (j * 7)
j++
if uint(cmd)&0xb80 == 0 || j == uint(len(b)) {
break
}
}
return size, b[j:]
}
func patchDelta(src, delta []byte) []byte {
if len(delta) < deltaSizeMin {
return nil
}
size, delta := deltaHeaderSize(delta)
if size != uint(len(src)) {
return nil
}
size, delta = deltaHeaderSize(delta)
origSize := size
dest := make([]byte, 0)
// var offset uint
var cmd byte
for {
cmd = delta[0]
delta = delta[1:]
if (cmd & 0x80) != 0 {
var cp_off, cp_size uint
if (cmd & 0x01) != 0 {
cp_off = uint(delta[0])
delta = delta[1:]
}
if (cmd & 0x02) != 0 {
cp_off |= uint(delta[0]) << 8
delta = delta[1:]
}
if (cmd & 0x04) != 0 {
cp_off |= uint(delta[0]) << 16
delta = delta[1:]
}
if (cmd & 0x08) != 0 {
cp_off |= uint(delta[0]) << 24
delta = delta[1:]
}
if (cmd & 0x10) != 0 {
cp_size = uint(delta[0])
delta = delta[1:]
}
if (cmd & 0x20) != 0 {
cp_size |= uint(delta[0]) << 8
delta = delta[1:]
}
if (cmd & 0x40) != 0 {
cp_size |= uint(delta[0]) << 16
delta = delta[1:]
}
if cp_size == 0 {
cp_size = 0x10000
}
if cp_off+cp_size < cp_off ||
cp_off+cp_size > uint(len(src)) ||
cp_size > origSize {
break
}
dest = append(dest, src[cp_off:cp_off+cp_size]...)
size -= cp_size
} else if cmd != 0 {
if uint(cmd) > origSize {
break
}
dest = append(dest, delta[0:uint(cmd)]...)
size -= uint(cmd)
delta = delta[uint(cmd):]
} else {
return nil
}
if size <= 0 {
break
}
}
return dest
}
func decodeOffset(src io.ByteReader, steps int64) (int64, error) {
b, err := src.ReadByte()
if err != nil {
return 0, err
}
var offset = int64(b & 0x7f)
for (b & 0x80) != 0 {
offset++ // WHY?
b, err = src.ReadByte()
if err != nil {
return 0, err
}
offset = (offset << 7) + int64(b&0x7f)
}
// offset needs to be aware of the bytes we read for `o.typ` and `o.size`
offset += steps
return -offset, nil
}
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