Add VLA extention header parser

Added VLA parser, builder and unit tests.

Author: enobufs

codecs/av1/obu/leb128.go

@@ -67,3 +67,19 @@ func ReadLeb128(in []byte) (uint, uint, error) {
 
 	return 0, 0, ErrFailedToReadLEB128
 }
+
+// WriteToLeb128 writes a uint to a LEB128 encoded byte slice.
+func WriteToLeb128(in uint) []byte {
+	b := make([]byte, 10)
+
+	for i := 0; i < len(b); i++ {
+		b[i] = byte(in & 0x7f)
+		in >>= 7
+		if in == 0 {
+			return b[:i+1]
+		}
+		b[i] |= 0x80
+	}
+
+	return b // unreachable
+}

codecs/av1/obu/leb128_test.go

@@ -4,7 +4,10 @@
 package obu
 
 import (
+	"encoding/hex"
 	"errors"
+	"fmt"
+	"math"
 	"testing"
 )
 
@@ -40,3 +43,33 @@ func TestReadLeb128(t *testing.T) {
 		t.Fatal("ReadLeb128 on a buffer with all MSB set should fail")
 	}
 }
+
+func TestWriteToLeb128(t *testing.T) {
+	type testVector struct {
+		value  uint
+		leb128 string
+	}
+	testVectors := []testVector{
+		{150, "9601"},
+		{240, "f001"},
+		{400, "9003"},
+		{720, "d005"},
+		{1200, "b009"},
+		{999999, "bf843d"},
+		{0, "00"},
+		{math.MaxUint32, "ffffffff0f"},
+	}
+
+	runTest := func(t *testing.T, v testVector) {
+		b := WriteToLeb128(v.value)
+		if v.leb128 != hex.EncodeToString(b) {
+			t.Errorf("Expected %s, got %s", v.leb128, hex.EncodeToString(b))
+		}
+	}
+
+	for _, v := range testVectors {
+		t.Run(fmt.Sprintf("encode %d", v.value), func(t *testing.T) {
+			runTest(t, v)
+		})
+	}
+}