Add a test for flatecut's Huffman decoder
diff --git a/lib/flatecut/flatecut.go b/lib/flatecut/flatecut.go
index cc4e7fc..ff8c3dd 100644
--- a/lib/flatecut/flatecut.go
+++ b/lib/flatecut/flatecut.go
@@ -125,10 +125,10 @@
// which results in:
//
// huffman{
-// counts: []uint32{
+// counts: [maxCodeBits + 1]uint32{
// 2: 1, 3: 5, 4: 2,
// },
-// symbols: []int32{
+// symbols: [maxNumCodes]int32{
// 0: 'F', 1: 'A', 2: 'B', 3: 'C', 4: 'D', 5: 'E', 6: 'G', 7: 'H',
// },
// }
diff --git a/lib/flatecut/flatecut_test.go b/lib/flatecut/flatecut_test.go
index 7c649ca..50abd39 100644
--- a/lib/flatecut/flatecut_test.go
+++ b/lib/flatecut/flatecut_test.go
@@ -39,3 +39,72 @@
func newReader(r io.Reader) (io.ReadCloser, error) {
return flate.NewReader(r), nil
}
+
+func TestHuffmanDecode(t *testing.T) {
+ // This exercises the "ABCDEFGH" example from RFC 1951 section 3.2.2,
+ // discussed in the "type huffman" doc comment.
+
+ const src = "HEADFACE"
+ codes := []string{
+ 'A': " 010",
+ 'B': " 011",
+ 'C': " 100",
+ 'D': " 101",
+ 'E': " 110",
+ 'F': " 00",
+ 'G': "1110",
+ 'H': "1111",
+ }
+
+ encoded := []byte(nil)
+ encBits := uint32(0)
+ encNBits := uint32(0)
+ for _, s := range src {
+ for _, c := range codes[s] {
+ if c == ' ' {
+ continue
+ }
+
+ if c == '1' {
+ encBits |= 1 << encNBits
+ }
+ encNBits++
+
+ if encNBits == 8 {
+ encoded = append(encoded, uint8(encBits))
+ encBits = 0
+ encNBits = 0
+ }
+ }
+ }
+ if encNBits > 0 {
+ encoded = append(encoded, uint8(encBits))
+ }
+
+ h := huffman{
+ counts: [maxCodeBits + 1]uint32{
+ 2: 1, 3: 5, 4: 2,
+ },
+ symbols: [maxNumCodes]int32{
+ 0: 'F', 1: 'A', 2: 'B', 3: 'C', 4: 'D', 5: 'E', 6: 'G', 7: 'H',
+ },
+ }
+
+ b := &bitstream{
+ bytes: encoded,
+ }
+
+ decoded := []byte(nil)
+ for _ = range src {
+ c := h.decode(b)
+ if c < 0 {
+ decoded = append(decoded, '!')
+ break
+ }
+ decoded = append(decoded, uint8(c))
+ }
+
+ if got, want := string(decoded), src; got != want {
+ t.Fatalf("got %q, want %q", got, want)
+ }
+}
