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strings: faster Count, Index

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Slightly better benchmarks for when string and separator are equivalent and also less branching in inner loops.
benchmark                        old ns/op    new ns/op    delta
BenchmarkGenericNoMatch               3430         3442   +0.35%
BenchmarkGenericMatch1               23590        22855   -3.12%
BenchmarkGenericMatch2              108031       105025   -2.78%
BenchmarkSingleMaxSkipping            2969         2704   -8.93%
BenchmarkSingleLongSuffixFail         2826         2572   -8.99%
BenchmarkSingleMatch                205268       197832   -3.62%
BenchmarkByteByteNoMatch               987          921   -6.69%
BenchmarkByteByteMatch                2014         1749  -13.16%
BenchmarkByteStringMatch              3083         3050   -1.07%
BenchmarkHTMLEscapeNew                 922          915   -0.76%
BenchmarkHTMLEscapeOld                1654         1570   -5.08%
BenchmarkByteByteReplaces            11897        11556   -2.87%
BenchmarkByteByteMap                  4485         4255   -5.13%
BenchmarkIndexRune                     174          121  -30.46%
BenchmarkIndexRuneFastPath              41           41   -0.24%
BenchmarkIndex                          45           44   -0.22%
BenchmarkMapNoChanges                  433          431   -0.46%
BenchmarkIndexHard1                4015336      3316490  -17.40%
BenchmarkIndexHard2                3976254      3395627  -14.60%
BenchmarkIndexHard3                3973158      3378329  -14.97%
BenchmarkCountHard1                4403549      3448512  -21.69%
BenchmarkCountHard2                4387437      3413059  -22.21%
BenchmarkCountHard3                4403891      3382661  -23.19%
BenchmarkIndexTorture                28354        25864   -8.78%
BenchmarkCountTorture                29625        27463   -7.30%
BenchmarkFields                   38752040     39169840   +1.08%
BenchmarkFieldsFunc               38797765     38888060   +0.23%

benchmark                         old MB/s     new MB/s  speedup
BenchmarkSingleMaxSkipping         3367.07      3697.62    1.10x
BenchmarkSingleLongSuffixFail       354.51       389.47    1.10x
BenchmarkSingleMatch                 73.07        75.82    1.04x
BenchmarkFields                      27.06        26.77    0.99x
BenchmarkFieldsFunc                  27.03        26.96    1.00x

R=dave, fullung, remyoudompheng, rsc
CC=golang-dev
https://golang.org/cl/7350045
This commit is contained in:
Donovan Hide 2013-02-19 10:36:15 -05:00 • committed by Russ Cox
parent 9704c80b93
commit 937f91e1da
2 changed files with 47 additions and 28 deletions
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67
src/pkg/strings/strings.go
View file

@ -59,21 +59,26 @@ func hashstr(sep string) (uint32, uint32) {
// Count counts the number of non-overlapping instances of sep in s.
func Count(s, sep string) int {
if sep == "" {
return utf8.RuneCountInString(s) + 1
}
c := sep[0]
n := 0
if len(sep) == 1 {
// special cases
switch {
case len(sep) == 0:
return utf8.RuneCountInString(s) + 1
case len(sep) == 1:
// special case worth making fast
c := sep[0]
for i := 0; i < len(s); i++ {
if s[i] == c {
n++
}
}
return n
}
if len(sep) > len(s) {
case len(sep) > len(s):
return 0
case len(sep) == len(s):
if sep == s {
return 1
}
return 0
}
hashsep, pow := hashstr(sep)
@ -82,17 +87,19 @@ func Count(s, sep string) int {
h = h*primeRK + uint32(s[i])
}
lastmatch := 0
for i := len(sep); ; i++ {
// Invariant: h = hash(s[i-l : i])
if h == hashsep && s[:len(sep)] == sep {
n++
lastmatch = len(sep)
}
for i := len(sep); i < len(s); {
h *= primeRK
h += uint32(s[i])
h -= pow * uint32(s[i-len(sep)])
i++
if h == hashsep && lastmatch <= i-len(sep) && s[i-len(sep):i] == sep {
n++
lastmatch = i
}
if i >= len(s) {
break
}
h = h*primeRK + uint32(s[i])
h -= pow * uint32(s[i-len(sep)])
}
return n
}
@ -115,11 +122,11 @@ func ContainsRune(s string, r rune) bool {
// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
func Index(s, sep string) int {
n := len(sep)
if n == 0 {
switch {
case n == 0:
return 0
}
c := sep[0]
if n == 1 {
case n == 1:
c := sep[0]
// special case worth making fast
for i := 0; i < len(s); i++ {
if s[i] == c {
@ -127,9 +134,12 @@ func Index(s, sep string) int {
}
}
return -1
}
// n > 1
if n > len(s) {
case n == len(s):
if sep == s {
return 0
}
return -1
case n > len(s):
return -1
}
// Hash sep.
@ -138,16 +148,17 @@ func Index(s, sep string) int {
for i := 0; i < n; i++ {
h = h*primeRK + uint32(s[i])
}
for i := n; ; i++ {
// Invariant: h = hash(s[i-n : i])
if h == hashsep && 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 && s[i-n:i] == sep {
return i - n
}
if i >= len(s) {
break
}
h = h*primeRK + uint32(s[i])
h -= pow * uint32(s[i-n])
}
return -1
}