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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bytealg
import (
"internal/cpu"
"unsafe"
)
// Offsets into internal/cpu records for use in assembly.
const (
offsetX86HasSSE42 = unsafe.Offsetof(cpu.X86.HasSSE42)
offsetX86HasAVX2 = unsafe.Offsetof(cpu.X86.HasAVX2)
offsetX86HasPOPCNT = unsafe.Offsetof(cpu.X86.HasPOPCNT)
offsetS390xHasVX = unsafe.Offsetof(cpu.S390X.HasVX)
offsetPPC64HasPOWER9 = unsafe.Offsetof(cpu.PPC64.IsPOWER9)
)
// MaxLen is the maximum length of the string to be searched for (argument b) in Index.
// If MaxLen is not 0, make sure MaxLen >= 4.
var MaxLen int = 32
// FIXME: the logic of HashStrBytes, HashStrRevBytes, IndexRabinKarpBytes and HashStr, HashStrRev,
// IndexRabinKarp are exactly the same, except that the types are different. Can we eliminate
// three of them without causing allocation?
// PrimeRK is the prime base used in Rabin-Karp algorithm.
const PrimeRK = 16777619
// HashStrBytes returns the hash and the appropriate multiplicative
// factor for use in Rabin-Karp algorithm.
func HashStrBytes(sep []byte) (uint32, uint32) {
hash := uint32(0)
for i := 0; i < len(sep); i++ {
hash = hash*PrimeRK + uint32(sep[i])
}
var pow, sq uint32 = 1, PrimeRK
for i := len(sep); i > 0; i >>= 1 {
if i&1 != 0 {
pow *= sq
}
sq *= sq
}
return hash, pow
}
// HashStr returns the hash and the appropriate multiplicative
// factor for use in Rabin-Karp algorithm.
func HashStr(sep string) (uint32, uint32) {
hash := uint32(0)
for i := 0; i < len(sep); i++ {
hash = hash*PrimeRK + uint32(sep[i])
}
var pow, sq uint32 = 1, PrimeRK
for i := len(sep); i > 0; i >>= 1 {
if i&1 != 0 {
pow *= sq
}
sq *= sq
}
return hash, pow
}
// HashStrRevBytes returns the hash of the reverse of sep and the
// appropriate multiplicative factor for use in Rabin-Karp algorithm.
func HashStrRevBytes(sep []byte) (uint32, uint32) {
hash := uint32(0)
for i := len(sep) - 1; i >= 0; i-- {
hash = hash*PrimeRK + uint32(sep[i])
}
var pow, sq uint32 = 1, PrimeRK
for i := len(sep); i > 0; i >>= 1 {
if i&1 != 0 {
pow *= sq
}
sq *= sq
}
return hash, pow
}
// HashStrRev returns the hash of the reverse of sep and the
// appropriate multiplicative factor for use in Rabin-Karp algorithm.
func HashStrRev(sep string) (uint32, uint32) {
hash := uint32(0)
for i := len(sep) - 1; i >= 0; i-- {
hash = hash*PrimeRK + uint32(sep[i])
}
var pow, sq uint32 = 1, PrimeRK
for i := len(sep); i > 0; i >>= 1 {
if i&1 != 0 {
pow *= sq
}
sq *= sq
}
return hash, pow
}
// IndexRabinKarpBytes uses the Rabin-Karp search algorithm to return the index of the
// first occurrence of substr in s, or -1 if not present.
func IndexRabinKarpBytes(s, sep []byte) int {
// Rabin-Karp search
hashsep, pow := HashStrBytes(sep)
n := len(sep)
var h uint32
for i := 0; i < n; i++ {
h = h*PrimeRK + uint32(s[i])
}
if h == hashsep && Equal(s[:n], sep) {
return 0
}
for i := n; i < len(s); {
h *= PrimeRK
h += uint32(s[i])
h -= pow * uint32(s[i-n])
i++
if h == hashsep && Equal(s[i-n:i], sep) {
return i - n
}
}
return -1
}
// IndexRabinKarp uses the Rabin-Karp search algorithm to return the index of the
// first occurrence of substr in s, or -1 if not present.
func IndexRabinKarp(s, substr string) int {
// Rabin-Karp search
hashss, pow := HashStr(substr)
n := len(substr)
var h uint32
for i := 0; i < n; i++ {
h = h*PrimeRK + uint32(s[i])
}
if h == hashss && s[:n] == substr {
return 0
}
for i := n; i < len(s); {
h *= PrimeRK
h += uint32(s[i])
h -= pow * uint32(s[i-n])
i++
if h == hashss && s[i-n:i] == substr {
return i - n
}
}
return -1
}
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