Add some benchmarks.

These are basically copied from the compress/flate package.

bench_test.go

@@ -0,0 +1,111 @@
+// The tests in this file are copied from the compress/flate package.
+
+// Copyright 2012 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 brotli
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"runtime"
+	"testing"
+)
+
+var suites = []struct{ name, file string }{
+	// Digits is the digits of the irrational number e. Its decimal representation
+	// does not repeat, but there are only 10 possible digits, so it should be
+	// reasonably compressible.
+	{"Digits", "testdata/e.txt"},
+	// Newton is Isaac Newtons's educational text on Opticks.
+	{"Newton", "testdata/Isaac.Newton-Opticks.txt"},
+}
+
+func BenchmarkDecode(b *testing.B) {
+	doBench(b, func(b *testing.B, buf0 []byte, level, n int) {
+		b.ReportAllocs()
+		b.StopTimer()
+		b.SetBytes(int64(n))
+
+		compressed := new(bytes.Buffer)
+		w := NewWriterLevel(compressed, level)
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			io.Copy(w, bytes.NewReader(buf0))
+		}
+		w.Close()
+		buf1 := compressed.Bytes()
+		buf0, compressed, w = nil, nil, nil
+		runtime.GC()
+		b.StartTimer()
+		for i := 0; i < b.N; i++ {
+			io.Copy(ioutil.Discard, NewReader(bytes.NewReader(buf1)))
+		}
+	})
+}
+
+var levelTests = []struct {
+	name  string
+	level int
+}{
+	{"Speed", BestSpeed},
+	{"Default", DefaultCompression},
+	{"Compression", BestCompression},
+}
+
+var sizes = []struct {
+	name string
+	n    int
+}{
+	{"1e4", 1e4},
+	{"1e5", 1e5},
+	{"1e6", 1e6},
+}
+
+func doBench(b *testing.B, f func(b *testing.B, buf []byte, level, n int)) {
+	for _, suite := range suites {
+		buf, err := ioutil.ReadFile(suite.file)
+		if err != nil {
+			b.Fatal(err)
+		}
+		if len(buf) == 0 {
+			b.Fatalf("test file %q has no data", suite.file)
+		}
+		for _, l := range levelTests {
+			for _, s := range sizes {
+				b.Run(suite.name+"/"+l.name+"/"+s.name, func(b *testing.B) {
+					f(b, buf, l.level, s.n)
+				})
+			}
+		}
+	}
+}
+
+func BenchmarkEncode(b *testing.B) {
+	doBench(b, func(b *testing.B, buf0 []byte, level, n int) {
+		b.ReportAllocs()
+		b.StopTimer()
+		b.SetBytes(int64(n))
+
+		buf1 := make([]byte, n)
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			copy(buf1[i:], buf0)
+		}
+		buf0 = nil
+		w := NewWriterLevel(ioutil.Discard, level)
+		runtime.GC()
+		b.StartTimer()
+		for i := 0; i < b.N; i++ {
+			w.Reset(ioutil.Discard)
+			w.Write(buf1)
+			w.Close()
+		}
+	})
+}