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bytes,internal/bytealg: eliminate IndexRabinKarpBytes using generics 

This is a follow-up to CL 538175.
This commit is contained in:
Jes Cok 2023-10-28 00:11:29 +08:00
parent b46aec0765
commit 812d36e57c
2 changed files with 4 additions and 33 deletions
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2
src/bytes/bytes.go
View File

@ -1331,7 +1331,7 @@ func Index(s, sep []byte) int {
// we should cutover at even larger average skips,
// because Equal becomes that much more expensive.
// This code does not take that effect into account.
j := bytealg.IndexRabinKarpBytes(s[i:], sep)
j := bytealg.IndexRabinKarp(s[i:], sep)
if j < 0 {
return -1
}

35
src/internal/bytealg/bytealg.go
View File

@ -24,10 +24,6 @@ const (
// If MaxLen is not 0, make sure MaxLen >= 4.
var MaxLen int
// FIXME: the logic of IndexRabinKarpBytes and IndexRabinKarp are exactly the same,
// except that the types are different.
// Can we eliminate one of them without causing allocation?
// PrimeRK is the prime base used in Rabin-Karp algorithm.
const PrimeRK = 16777619
@ -65,34 +61,9 @@ func HashStrRev[T string | []byte](sep T) (uint32, uint32) {
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 := HashStr(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 {
func IndexRabinKarp[T string | []byte](s, substr T) int {
// Rabin-Karp search
hashss, pow := HashStr(substr)
n := len(substr)
@ -100,7 +71,7 @@ func IndexRabinKarp(s, substr string) int {
for i := 0; i < n; i++ {
h = h*PrimeRK + uint32(s[i])
}
if h == hashss && s[:n] == substr {
if h == hashss && string(s[:n]) == string(substr) {
return 0
}
for i := n; i < len(s); {
@ -108,7 +79,7 @@ func IndexRabinKarp(s, substr string) int {
h += uint32(s[i])
h -= pow * uint32(s[i-n])
i++
if h == hashss && s[i-n:i] == substr {
if h == hashss && string(s[i-n:i]) == string(substr) {
return i - n
}
}