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rabinkarp.go
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/
rabinkarp.go
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package rdiff
type RabinkarpChecksum struct {
count uint64
hash, multiplier uint32
}
func NewRabinkarpChecksum() *RabinkarpChecksum {
return &RabinkarpChecksum{
count: 0,
hash: RabinkarpSeed,
multiplier: 1,
}
}
func (r *RabinkarpChecksum) Update(buf []byte) {
length := len(buf)
r.count += uint64(length)
for i := 0; i < length; i++ {
r.hash = r.hash*RabinkarpMultiplier + uint32(buf[i])
r.multiplier *= RabinkarpMultiplier
}
}
func (r *RabinkarpChecksum) Rotate(out, in byte) {
r.hash = r.hash*RabinkarpMultiplier + uint32(in) - r.multiplier*(uint32(out)+RabinkarpAdjustment)
}
func (r *RabinkarpChecksum) Rollin(in byte) {
r.hash = r.hash*RabinkarpMultiplier + uint32(in)
r.count++
r.multiplier *= RabinkarpMultiplier
}
func (r *RabinkarpChecksum) Rollout(out byte) {
r.count--
r.multiplier *= RabinkarpMultiplierInverseModular
r.hash -= r.multiplier * (uint32(out) + RabinkarpAdjustment)
}
func (r *RabinkarpChecksum) Digest() uint32 {
return r.hash
}
func (r *RabinkarpChecksum) Reset() {
r.count = 0
r.hash = RabinkarpSeed
r.multiplier = 1
}