From 838d5dd5d68afafbf3f1b27dae96188bec3131bf Mon Sep 17 00:00:00 2001
From: Saxon <saxon@ausocean.org>
Date: Wed, 28 Aug 2019 10:09:27 +0930
Subject: [PATCH] codec/h264/h264dec: added level_prefix parsing process and
 test

---
 codec/h264/h264dec/cavlc.go      | 46 ++++++++++++++++++++++++++
 codec/h264/h264dec/cavlc_test.go | 55 ++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 codec/h264/h264dec/cavlc.go
 create mode 100644 codec/h264/h264dec/cavlc_test.go

diff --git a/codec/h264/h264dec/cavlc.go b/codec/h264/h264dec/cavlc.go
new file mode 100644
index 00000000..c477a490
--- /dev/null
+++ b/codec/h264/h264dec/cavlc.go
@@ -0,0 +1,46 @@
+/*
+DESCRIPTION
+  cavlc.go provides utilities for context-adaptive variable-length coding
+  for the parsing of H.264 syntax structure fields.
+
+AUTHORS
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2019 the Australian Ocean Lab (AusOcean).
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License
+  in gpl.txt.  If not, see http://www.gnu.org/licenses.
+*/
+
+package h264dec
+
+import (
+	"fmt"
+
+	"bitbucket.org/ausocean/av/codec/h264/h264dec/bits"
+)
+
+// parseLevelPrefix parses the level_prefix variable as specified by the process
+// outlined in section 9.2.2.1 in the specifications.
+func parseLevelPrefix(br *bits.BitReader) (int, error) {
+	zeros := -1
+	for b := 0; b != 1; zeros++ {
+		_b, err := br.ReadBits(1)
+		if err != nil {
+			return -1, fmt.Errorf("could not read bit, failed with error: %v", err)
+		}
+		b = int(_b)
+	}
+	return zeros, nil
+}
diff --git a/codec/h264/h264dec/cavlc_test.go b/codec/h264/h264dec/cavlc_test.go
new file mode 100644
index 00000000..a6740858
--- /dev/null
+++ b/codec/h264/h264dec/cavlc_test.go
@@ -0,0 +1,55 @@
+/*
+DESCRIPTION
+  cavlc_test.go provides testing for functionality in cavlc.go.
+
+AUTHORS
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2019 the Australian Ocean Lab (AusOcean).
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License
+  in gpl.txt.  If not, see http://www.gnu.org/licenses.
+*/
+
+package h264dec
+
+import (
+	"bytes"
+	"testing"
+
+	"bitbucket.org/ausocean/av/codec/h264/h264dec/bits"
+)
+
+func TestParseLevelPrefix(t *testing.T) {
+	tests := []struct {
+		in   string
+		want int
+	}{
+		{in: "00001", want: 4},
+		{in: "0000001", want: 6},
+		{in: "1", want: 0},
+	}
+
+	for i, test := range tests {
+		s, _ := binToSlice(test.in)
+		l, err := parseLevelPrefix(bits.NewBitReader(bytes.NewReader(s)))
+		if err != nil {
+			t.Errorf("did not expect error: %v, for test %d", err, i)
+		}
+
+		if l != test.want {
+			t.Errorf("did not get expected result for test %d\nGot: %d\nWant: %d\n", i, l, test.want)
+		}
+	}
+}