mirror of
https://github.com/go-gitea/gitea
synced 2024-12-29 12:04:28 +00:00
67 lines
1.6 KiB
Go
Vendored
67 lines
1.6 KiB
Go
Vendored
// Copyright 2014-2021 Ulrich Kunitz. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package hash
|
|
|
|
// A is the default constant for Robin-Karp rolling hash. This is a random
|
|
// prime.
|
|
const A = 0x97b548add41d5da1
|
|
|
|
// RabinKarp supports the computation of a rolling hash.
|
|
type RabinKarp struct {
|
|
A uint64
|
|
// a^n
|
|
aOldest uint64
|
|
h uint64
|
|
p []byte
|
|
i int
|
|
}
|
|
|
|
// NewRabinKarp creates a new RabinKarp value. The argument n defines the
|
|
// length of the byte sequence to be hashed. The default constant will will be
|
|
// used.
|
|
func NewRabinKarp(n int) *RabinKarp {
|
|
return NewRabinKarpConst(n, A)
|
|
}
|
|
|
|
// NewRabinKarpConst creates a new RabinKarp value. The argument n defines the
|
|
// length of the byte sequence to be hashed. The argument a provides the
|
|
// constant used to compute the hash.
|
|
func NewRabinKarpConst(n int, a uint64) *RabinKarp {
|
|
if n <= 0 {
|
|
panic("number of bytes n must be positive")
|
|
}
|
|
aOldest := uint64(1)
|
|
// There are faster methods. For the small n required by the LZMA
|
|
// compressor O(n) is sufficient.
|
|
for i := 0; i < n; i++ {
|
|
aOldest *= a
|
|
}
|
|
return &RabinKarp{
|
|
A: a, aOldest: aOldest,
|
|
p: make([]byte, 0, n),
|
|
}
|
|
}
|
|
|
|
// Len returns the length of the byte sequence.
|
|
func (r *RabinKarp) Len() int {
|
|
return cap(r.p)
|
|
}
|
|
|
|
// RollByte computes the hash after x has been added.
|
|
func (r *RabinKarp) RollByte(x byte) uint64 {
|
|
if len(r.p) < cap(r.p) {
|
|
r.h += uint64(x)
|
|
r.h *= r.A
|
|
r.p = append(r.p, x)
|
|
} else {
|
|
r.h -= uint64(r.p[r.i]) * r.aOldest
|
|
r.h += uint64(x)
|
|
r.h *= r.A
|
|
r.p[r.i] = x
|
|
r.i = (r.i + 1) % cap(r.p)
|
|
}
|
|
return r.h
|
|
}
|