// use rollsum do weak sum
func weakSum(p []byte) (s uint32) {
var rs rollsum.Rollsum
rs.Init()
rs.Update(p)
return rs.Digest()
}
func (d *delta) genDelta(src io.ReadSeeker, srcLen int64) (err error) {
var (
c byte
p []byte
rs rollsum.Rollsum
rb *rotateBuffer
srcPos int64
matchAt int64
blockLen int
)
if d.debug {
d.dumpSign()
}
blockLen = int(d.sig.block_len)
rb = NewRotateBuffer(srcLen, d.sig.block_len, src)
p, srcPos, err = rb.rollFirst()
if err == nil {
// 计算初始weaksum
rs.Init()
rs.Update(p)
for err == nil {
// srcPos是当前读取src文件的绝对位置，matchAt对应于dstSig和dst文件的位置
matchAt = d.findMatch(p, srcPos, rs.Digest())
if matchAt < 0 {
p, c, srcPos, err = rb.rollByte()
if err != nil {
break
}
rs.Rotate(c, p[blockLen-1])
} else {
p, srcPos, err = rb.rollBlock()
rs.Init()
if err != nil {
break
}
rs.Update(p)
}
}
} else if err == noBytesLeft {
// reader没有内容
if d.debug {
fmt.Println("reader has no content:", srcLen)
}
err = nil
return
}
if err != noBytesLeft && err != notEnoughBytes {
// 出错
return
}
if d.debug {
fmt.Printf("rotate buffer left no more than a block: block=%d start=%d end=%d absHead=%d absTail=%d eof=%v\n",
blockLen, rb.start, rb.end, rb.absHead, rb.absTail, rb.eof)
}
if p, c, srcPos, err = rb.rollLeft(); err == nil {
rs.Init()
rs.Update(p)
for err == nil {
matchAt = d.findMatch(p, srcPos, rs.Digest())
if matchAt >= 0 {
// 剩余的内容已经匹配到，不需要继续处理
break
} else {
p, c, srcPos, err = rb.rollLeft()
if err != nil {
break
}
rs.Rollout(c)
}
}
} else {
if d.debug {
fmt.Println(string(p), c, srcPos, err)
}
}
if err == noBytesLeft || err == nil {
if d.debug {
fmt.Println("last match stat:", d.ms.match, d.ms.pos, d.ms.length)
}
d.mss = append(d.mss, d.ms)
err = nil
}
return
}