strconv: some allocation tests

R=rsc, r
CC=golang-dev
https://golang.org/cl/5477084

src/pkg/strconv/ftoa_test.go

@@ -149,6 +149,23 @@ func TestFtoa(t *testing.T) {
 	}
 }
 
+func TestAppendFloatDoesntAllocate(t *testing.T) {
+	n := numAllocations(func() {
+		var buf [64]byte
+		AppendFloat(buf[:0], 1.23, 'g', 5, 64)
+	})
+	want := 1 // TODO(bradfitz): this might be 0, once escape analysis is better
+	if n != want {
+		t.Errorf("with local buffer, did %d allocations, want %d", n, want)
+	}
+	n = numAllocations(func() {
+		AppendFloat(globalBuf[:0], 1.23, 'g', 5, 64)
+	})
+	if n != 0 {
+		t.Errorf("with reused buffer, did %d allocations, want 0", n)
+	}
+}
+
 func BenchmarkFormatFloatDecimal(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		FormatFloat(33909, 'g', -1, 64)

src/pkg/strconv/itoa_test.go

@@ -5,6 +5,7 @@
 package strconv_test
 
 import (
+	"runtime"
 	. "strconv"
 	"testing"
 )
@@ -125,6 +126,33 @@ func TestUitoa(t *testing.T) {
 	}
 }
 
+func numAllocations(f func()) int {
+	runtime.UpdateMemStats()
+	n0 := runtime.MemStats.Mallocs
+	f()
+	runtime.UpdateMemStats()
+	return int(runtime.MemStats.Mallocs - n0)
+}
+
+var globalBuf [64]byte
+
+func TestAppendUintDoesntAllocate(t *testing.T) {
+	n := numAllocations(func() {
+		var buf [64]byte
+		AppendInt(buf[:0], 123, 10)
+	})
+	want := 1 // TODO(bradfitz): this might be 0, once escape analysis is better
+	if n != want {
+		t.Errorf("with local buffer, did %d allocations, want %d", n, want)
+	}
+	n = numAllocations(func() {
+		AppendInt(globalBuf[:0], 123, 10)
+	})
+	if n != 0 {
+		t.Errorf("with reused buffer, did %d allocations, want 0", n)
+	}
+}
+
 func BenchmarkFormatInt(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for _, test := range itob64tests {