Add and AddByte

R=rsc
DELTA=83  (83 added, 0 deleted, 0 changed)
OCL=34584
CL=34584

diff --git a/src/pkg/bytes/bytes.go b/src/pkg/bytes/bytes.go
index 5375fecaa232eec487beb353177491c211f6363f..52aa8cdf40c718acdd8e06af14c5b87c43eb9de4 100644 (file)
--- a/src/pkg/bytes/bytes.go
+++ b/src/pkg/bytes/bytes.go
@@ -260,3 +260,45 @@ func TrimSpace(s []byte) []byte {
        }
        return s[start:end];
 }
+
+// How big to make a byte array when growing.
+// Heuristic: Scale by 50% to give n log n time.
+func resize(n int) int {
+       if n < 16 {
+               n = 16
+       }
+       return n + n/2;
+}
+
+// Add appends the contents of t to the end of s and returns the result.
+// If s has enough capacity, it is extended in place; otherwise a
+// new array is allocated and returned.
+func Add(s, t []byte) []byte {
+       lens := len(s);
+       lent := len(t);
+       if lens + lent <= cap(s) {
+               s = s[0:lens+lent];
+       } else {
+               news := make([]byte, lens+lent, resize(lens+lent));
+               Copy(news, s);
+               s = news;
+       }
+       Copy(s[lens:lens+lent], t);
+       return s;
+}
+
+// AddByte appends byte b to the end of s and returns the result.
+// If s has enough capacity, it is extended in place; otherwise a
+// new array is allocated and returned.
+func AddByte(s []byte, t byte) []byte {
+       lens := len(s);
+       if lens + 1 <= cap(s) {
+               s = s[0:lens+1];
+       } else {
+               news := make([]byte, lens+1, resize(lens+1));
+               Copy(news, s);
+               s = news;
+       }
+       s[lens] = t;
+       return s;
+}

diff --git a/src/pkg/bytes/bytes_test.go b/src/pkg/bytes/bytes_test.go
index a7667ec21e2f8c95819af8a30a807cd243bd56a3..8443480e56f95492e73a89810510810a3cfef33b 100644 (file)
--- a/src/pkg/bytes/bytes_test.go
+++ b/src/pkg/bytes/bytes_test.go
@@ -121,6 +121,7 @@ var splittests = []SplitTest {
        SplitTest{ "123",       "",     2, []string{"1", "23"} },
        SplitTest{ "123",       "",     17, []string{"1", "2", "3"} },
 }
+
 func TestSplit(t *testing.T) {
        for _, tt := range splittests {
                a := Split(strings.Bytes(tt.s), strings.Bytes(tt.sep), tt.n);
@@ -261,3 +262,43 @@ func TestToLower(t *testing.T) {
 func TestTrimSpace(t *testing.T) {
        runStringTests(t, TrimSpace, "TrimSpace", trimSpaceTests);
 }
+
+type AddTest struct {
+       s, t string;
+       cap     int;
+}
+var addtests = []AddTest {
+       AddTest{ "", "", 0 },
+       AddTest{ "a", "", 1 },
+       AddTest{ "a", "b", 1 },
+       AddTest{ "abc", "def", 100 },
+}
+
+func TestAdd(t *testing.T) {
+       for i, test := range addtests {
+               b := make([]byte, len(test.s), test.cap);
+               for i := 0; i < len(test.s); i++ {
+                       b[i] = test.s[i]
+               }
+               b = Add(b, strings.Bytes(test.t));
+               if string(b) != test.s+test.t {
+                       t.Errorf("Add(%q,%q) = %q", test.s, test.t, string(b));
+               }
+       }
+}
+
+func TestAddByte(t *testing.T) {
+       const N = 2e5;
+       b := make([]byte, 0);
+       for i := 0; i < N; i++ {
+               b = AddByte(b, byte(i))
+       }
+       if len(b) != N {
+               t.Errorf("AddByte: too small; expected %d got %d", N, len(b));
+       }
+       for i, c := range b {
+               if c != byte(i) {
+                       t.Fatalf("AddByte: b[%d] should be %d is %d", i, c, byte(i));
+               }
+       }
+}