bytes, strings: optimize Cut for single-byte separators

Optimize the Cut function in both the bytes and strings packages to immediately return slices when the separator is a single byte (or character), avoiding more complex index searching logic. This change can significantly reduce the execution time for these specific cases, as benchmark tests added to each package demonstrate improvements. The optimization checks if the length of the separator is one before proceeding with the existing search strategy. If so, it uses IndexByte for a faster lookup of the separator's position. Additionally, benchmark tests have been added for both packages to demonstrate the performance benefits of this optimization across various scenarios. goos: darwin goarch: arm64 pkg: strings cpu: Apple M2 Max │ old-cut.txt │ new-cut.txt │ │ sec/op │ sec/op vs base │ Cut/Cut-One/2-12 4.026n ± 2% 3.274n ± 2% -18.68% (p=0.000 n=10) Cut/Cut-Two/2-12 8.093n ± 0% 8.357n ± 0% +3.27% (p=0.000 n=10) Cut/Cut-One/4-12 4.048n ± 1% 3.324n ± 2% -17.91% (p=0.000 n=10) Cut/Cut-Two/4-12 8.105n ± 0% 8.377n ± 1% +3.35% (p=0.000 n=10) Cut/Cut-One/8-12 4.089n ± 1% 3.290n ± 1% -19.53% (p=0.000 n=10) Cut/Cut-Two/8-12 8.107n ± 1% 8.359n ± 1% +3.10% (p=0.000 n=10) Cut/Cut-One/16-12 4.127n ± 1% 3.328n ± 1% -19.35% (p=0.000 n=10) Cut/Cut-Two/16-12 8.119n ± 1% 8.374n ± 1% +3.15% (p=0.000 n=10) Cut/Cut-One/32-12 4.545n ± 2% 3.675n ± 1% -19.14% (p=0.000 n=10) Cut/Cut-Two/32-12 8.708n ± 1% 8.963n ± 1% +2.92% (p=0.000 n=10) Cut/Cut-One/64-12 4.825n ± 2% 4.146n ± 1% -14.08% (p=0.000 n=10) Cut/Cut-Two/64-12 9.286n ± 0% 9.315n ± 1% ~ (p=0.105 n=10) geomean 5.983n 5.486n -8.32% │ old-cut.txt │ new-cut.txt │ │ B/op │ B/op vs base │ Cut/Cut-One/2-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/2-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/4-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/4-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/8-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/8-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/16-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/16-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/32-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/32-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/64-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/64-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ geomean ² +0.00% ² ¹ all samples are equal ² summaries must be >0 to compute geomean │ old-cut.txt │ new-cut.txt │ │ allocs/op │ allocs/op vs base │ Cut/Cut-One/2-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/2-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/4-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/4-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/8-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/8-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/16-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/16-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/32-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/32-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-One/64-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ Cut/Cut-Two/64-12 0.000 ± 0% 0.000 ± 0% ~ (p=1.000 n=10) ¹ geomean ² +0.00% ² ¹ all samples are equal ² summaries must be >0 to compute geomean For #67101
golang · May 1, 2024 · 90f46f8 · 90f46f8
1 parent c5698e3
commit 90f46f8
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diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
@@ -1330,6 +1330,12 @@ func Index(s, sep []byte) int {
 //
 // Cut returns slices of the original slice s, not copies.
 func Cut(s, sep []byte) (before, after []byte, found bool) {
+	if len(sep) == 1 {
+		if i := IndexByte(s, sep[0]); i >= 0 {
+			return s[:i], s[i+1:], true
+		}
+		return s, nil, false
+	}
 	if i := Index(s, sep); i >= 0 {
 		return s[:i], s[i+len(sep):], true
 	}

diff --git a/src/bytes/bytes_test.go b/src/bytes/bytes_test.go
@@ -2263,3 +2263,31 @@ func TestClone(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkCut(b *testing.B) {
+	b.ReportAllocs()
+
+	for _, skip := range [...]int{2, 4, 8, 16, 32, 64} {
+		s := Repeat(append(append(Repeat([]byte(" "), skip), 'a', 'a'), Repeat([]byte(" "), skip)...), 1<<16/skip)
+		b.Run(fmt.Sprintf("Cut-One/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, []byte{'a'})
+			}
+		})
+		b.Run(fmt.Sprintf("Cut-Two/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, []byte{'a', 'a'})
+			}
+		})
+		b.Run(fmt.Sprintf("Cut-One-Nil/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, []byte{'c'})
+			}
+		})
+		b.Run(fmt.Sprintf("Cut-Two-Nil/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, []byte{'c', 'c'})
+			}
+		})
+	}
+}
diff --git a/src/internal/stringslite/strings.go b/src/internal/stringslite/strings.go
@@ -103,6 +103,12 @@ func Index(s, substr string) int {
 }
 
 func Cut(s, sep string) (before, after string, found bool) {
+	if len(sep) == 1 {
+		if i := IndexByte(s, sep[0]); i >= 0 {
+			return s[:i], s[i+1:], true
+		}
+		return s, "", false
+	}
 	if i := Index(s, sep); i >= 0 {
 		return s[:i], s[i+len(sep):], true
 	}

diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
@@ -2071,3 +2071,31 @@ func BenchmarkReplaceAll(b *testing.B) {
 		stringSink = ReplaceAll("banana", "a", "<>")
 	}
 }
+
+func BenchmarkCut(b *testing.B) {
+	b.ReportAllocs()
+
+	for _, skip := range [...]int{2, 4, 8, 16, 32, 64} {
+		s := Repeat(Repeat(" ", skip)+"aa"+Repeat(" ", skip), 1<<16/skip)
+		b.Run(fmt.Sprintf("Cut-One/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, "a")
+			}
+		})
+		b.Run(fmt.Sprintf("Cut-Two/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, "aa")
+			}
+		})
+		b.Run(fmt.Sprintf("Cut-One-Nil/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, "c")
+			}
+		})
+		b.Run(fmt.Sprintf("Cut-Two-Nil/%d", skip), func(b *testing.B) {
+			for range b.N {
+				_, _, _ = Cut(s, "cc")
+			}
+		})
+	}
+}