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strings: speed up Fields
- use a string lookup to detect if a single byte is a space character - determine the exact number of fields for ASCII and a possibly underestimated number of fields for non ASCII strings by doing a separate byte for byte scan of the input string before collecting the fields in an extra pass - provide a fast path for ASCII only strings when collecting the fields - avoid utf8.DecodeRuneInString and unicode.IsSpace for ASCII characters Used golang.org/cl/33108 from Joe Tsai as starting point. name old time/op new time/op delta Fields/ASCII/16 284ns ± 1% 116ns ± 2% -59.30% (p=0.000 n=9+10) Fields/ASCII/256 3.81µs ± 1% 0.80µs ± 1% -79.10% (p=0.000 n=10+10) Fields/ASCII/4096 61.4µs ± 1% 12.3µs ± 1% -79.96% (p=0.000 n=10+9) Fields/ASCII/65536 982µs ± 1% 235µs ± 0% -76.04% (p=0.000 n=10+9) Fields/ASCII/1048576 16.7ms ± 2% 5.4ms ± 1% -67.52% (p=0.000 n=10+10) Fields/Mixed/16 314ns ± 1% 168ns ± 1% -46.33% (p=0.000 n=9+10) Fields/Mixed/256 3.92µs ± 1% 1.17µs ± 1% -70.19% (p=0.000 n=10+10) Fields/Mixed/4096 69.1µs ± 1% 19.0µs ± 1% -72.53% (p=0.000 n=10+10) Fields/Mixed/65536 1.12ms ± 1% 0.39ms ± 0% -65.37% (p=0.000 n=10+9) Fields/Mixed/1048576 19.0ms ± 2% 7.3ms ± 4% -61.75% (p=0.000 n=10+9) name old speed new speed delta Fields/ASCII/16 56.3MB/s ± 1% 138.1MB/s ± 2% +145.31% (p=0.000 n=9+10) Fields/ASCII/256 67.1MB/s ± 1% 321.0MB/s ± 1% +378.26% (p=0.000 n=10+10) Fields/ASCII/4096 66.7MB/s ± 1% 333.0MB/s ± 1% +398.97% (p=0.000 n=10+9) Fields/ASCII/65536 66.7MB/s ± 1% 278.4MB/s ± 0% +317.39% (p=0.000 n=10+9) Fields/ASCII/1048576 62.7MB/s ± 2% 192.9MB/s ± 1% +207.82% (p=0.000 n=10+10) Fields/Mixed/16 51.0MB/s ± 2% 94.9MB/s ± 1% +85.87% (p=0.000 n=10+10) Fields/Mixed/256 65.4MB/s ± 1% 219.2MB/s ± 1% +235.33% (p=0.000 n=10+10) Fields/Mixed/4096 59.3MB/s ± 1% 215.7MB/s ± 1% +263.98% (p=0.000 n=10+10) Fields/Mixed/65536 58.6MB/s ± 1% 169.1MB/s ± 0% +188.73% (p=0.000 n=10+9) Fields/Mixed/1048576 55.1MB/s ± 2% 144.0MB/s ± 4% +161.44% (p=0.000 n=10+9) Updates #19789 Updates #17856 Change-Id: If2ce1479542702e9cd65a82a462ba55ac8eb3876 Reviewed-on: https://go-review.googlesource.com/37959 Run-TryBot: Martin Möhrmann <moehrmann@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
This commit is contained in:
Martin Möhrmann
parent
5cadc91b3c
commit
bebfd4ba41
@ -290,11 +290,118 @@ func SplitAfter(s, sep string) []string {
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return genSplit(s, sep, len(sep), -1)
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}
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var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
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// Fields splits the string s around each instance of one or more consecutive white space
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// characters, as defined by unicode.IsSpace, returning an array of substrings of s or an
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// empty list if s contains only white space.
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func Fields(s string) []string {
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return FieldsFunc(s, unicode.IsSpace)
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// First count the fields.
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// This is an exact count if s is ASCII, otherwise it is an approximation.
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n := 0
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wasSpace := 1
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// setBits is used to track which bits are set in the bytes of s.
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setBits := uint8(0)
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for i := 0; i < len(s); i++ {
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r := s[i]
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setBits |= r
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isSpace := int(asciiSpace[r])
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n += wasSpace & ^isSpace
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wasSpace = isSpace
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}
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if setBits < utf8.RuneSelf { // ASCII fast path
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a := make([]string, n)
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na := 0
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fieldStart := 0
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i := 0
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// Skip spaces in the front of the input.
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for i < len(s) && asciiSpace[s[i]] != 0 {
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i++
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}
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fieldStart = i
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for i < len(s) {
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if asciiSpace[s[i]] == 0 {
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i++
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continue
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}
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a[na] = s[fieldStart:i]
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na++
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i++
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// Skip spaces in between fields.
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for i < len(s) && asciiSpace[s[i]] != 0 {
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i++
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}
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fieldStart = i
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}
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if fieldStart < len(s) { // Last field might end at EOF.
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a[na] = s[fieldStart:]
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}
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return a
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}
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// Some runes in the input string are not ASCII.
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// Same general approach as in the ASCII path but
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// uses DecodeRuneInString and unicode.IsSpace if
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// a non-ASCII rune needs to be decoded and checked
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// if it corresponds to a space.
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a := make([]string, 0, n)
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fieldStart := 0
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i := 0
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// Skip spaces in the front of the input.
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for i < len(s) {
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if c := s[i]; c < utf8.RuneSelf {
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if asciiSpace[c] == 0 {
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break
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}
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i++
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} else {
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r, w := utf8.DecodeRuneInString(s[i:])
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if !unicode.IsSpace(r) {
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break
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}
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i += w
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}
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}
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fieldStart = i
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for i < len(s) {
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if c := s[i]; c < utf8.RuneSelf {
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if asciiSpace[c] == 0 {
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i++
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continue
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}
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a = append(a, s[fieldStart:i])
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i++
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} else {
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r, w := utf8.DecodeRuneInString(s[i:])
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if !unicode.IsSpace(r) {
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i += w
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continue
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}
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a = append(a, s[fieldStart:i])
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i += w
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}
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// Skip spaces in between fields.
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for i < len(s) {
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if c := s[i]; c < utf8.RuneSelf {
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if asciiSpace[c] == 0 {
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break
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}
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i++
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} else {
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r, w := utf8.DecodeRuneInString(s[i:])
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if !unicode.IsSpace(r) {
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break
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}
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i += w
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}
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}
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fieldStart = i
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}
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if fieldStart < len(s) { // Last field might end at EOF.
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a = append(a, s[fieldStart:])
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}
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return a
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}
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// FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
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@ -452,6 +452,7 @@ var fieldstests = []FieldsTest{
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{"", []string{}},
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{" ", []string{}},
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{" \t ", []string{}},
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{"\u2000", []string{}},
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{" abc ", []string{"abc"}},
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{"1 2 3 4", []string{"1", "2", "3", "4"}},
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{"1 2 3 4", []string{"1", "2", "3", "4"}},
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@ -459,6 +460,9 @@ var fieldstests = []FieldsTest{
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{"1\u20002\u20013\u20024", []string{"1", "2", "3", "4"}},
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{"\u2000\u2001\u2002", []string{}},
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{"\n™\t™\n", []string{"™", "™"}},
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{"\n\u20001™2\u2000 \u2001 ™", []string{"1™2", "™"}},
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{"\n1\uFFFD \uFFFD2\u20003\uFFFD4", []string{"1\uFFFD", "\uFFFD2", "3\uFFFD4"}},
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{"1\xFF\u2000\xFF2\xFF \xFF", []string{"1\xFF", "\xFF2\xFF", "\xFF"}},
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{faces, []string{faces}},
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}
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@ -1473,19 +1477,55 @@ var makeFieldsInput = func() string {
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return string(x)
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}
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var fieldsInput = makeFieldsInput()
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var makeFieldsInputASCII = func() string {
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x := make([]byte, 1<<20)
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// Input is ~10% space, rest ASCII non-space.
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for i := range x {
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if rand.Intn(10) == 0 {
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x[i] = ' '
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} else {
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x[i] = 'x'
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}
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}
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return string(x)
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}
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var stringdata = []struct{ name, data string }{
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{"ASCII", makeFieldsInputASCII()},
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{"Mixed", makeFieldsInput()},
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}
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func BenchmarkFields(b *testing.B) {
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b.SetBytes(int64(len(fieldsInput)))
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for _, sd := range stringdata {
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b.Run(sd.name, func(b *testing.B) {
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for j := 1 << 4; j <= 1<<20; j <<= 4 {
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b.Run(fmt.Sprintf("%d", j), func(b *testing.B) {
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b.ReportAllocs()
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b.SetBytes(int64(j))
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data := sd.data[:j]
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for i := 0; i < b.N; i++ {
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Fields(fieldsInput)
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Fields(data)
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}
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})
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}
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})
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}
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}
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func BenchmarkFieldsFunc(b *testing.B) {
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b.SetBytes(int64(len(fieldsInput)))
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for _, sd := range stringdata {
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b.Run(sd.name, func(b *testing.B) {
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for j := 1 << 4; j <= 1<<20; j <<= 4 {
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b.Run(fmt.Sprintf("%d", j), func(b *testing.B) {
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b.ReportAllocs()
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b.SetBytes(int64(j))
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data := sd.data[:j]
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for i := 0; i < b.N; i++ {
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FieldsFunc(fieldsInput, unicode.IsSpace)
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FieldsFunc(data, unicode.IsSpace)
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}
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})
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}
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})
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}
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}
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