codec/h264: added decode folder, decode/parse.go and first function in parse.go.

Added decode folder which will contain the h264 decoder and utilities. Added first file parse.go, which contains parsing
processes for syntax elements.

codec/h264/decode/parse.go

@@ -0,0 +1,53 @@
+/*
+NAME
+  parse.go
+
+DESCRIPTION
+  parse.go provides parsing processes for syntax elements of different
+  descriptors specified in 7.2 of ITU-T H.264.
+
+AUTHOR
+  Saxon Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2017 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
+  along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
+*/
+
+package decode
+
+import (
+	"math"
+
+	"github.com/icza/bitio"
+)
+
+// readUe parses a syntax element of ue(v) descriptor, i.e. an unsigned integer
+// Exp-Golomb-coded element. This process is specified in 9.1.
+func readUe(r bitio.Reader) (int, error) {
+	nZeros := -1
+	var err error
+	for b := uint64(0); b == 0; nZeros++ {
+		b, err = r.ReadBits(1)
+		if err != nil {
+			return 0, err
+		}
+	}
+	rem, err := r.ReadBits(byte(nZeros))
+	if err != nil {
+		return 0, err
+	}
+	return int(math.Pow(float64(2), float64(nZeros)) - 1 + float64(rem)), nil
+}