1 files changed, 116 insertions, 0 deletions
diff --git a/gpr/source/lib/vc5_decoder/syntax.c b/gpr/source/lib/vc5_decoder/syntax.c
new file mode 100755
index 0000000..f0c4b58
--- /dev/null
+++ b/gpr/source/lib/vc5_decoder/syntax.c
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+/*! @file syntax.c
+ *
+ *  @brief Implementation of functions for parsing the bitstream syntax of encoded samples.
+ *
+ *  (C) Copyright 2018 GoPro Inc (http://gopro.com/).
+ *
+ *  Licensed under either:
+ *  - Apache License, Version 2.0, http://www.apache.org/licenses/LICENSE-2.0
+ *  - MIT license, http://opensource.org/licenses/MIT
+ *  at your option.
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#include "headers.h"
+
+//! Size of a tag or value (in bits)
+#define BITSTREAM_TAG_SIZE				16
+
+/*!
+	@brief Read the next tag-valie pair from the bitstream.
+
+	The next tag is read from the bitstream and the next value that
+	immediately follows the tag in the bitstreeam are read from the
+	bitstream.
+
+	The value may be the length of the payload in bytes or the value
+	may be a single scalar.  This routine only reads the next tag and
+	value and does not intepret the tag or value and does not read any
+	data that may follow the segment in the bitstream.
+
+	The tag and value are interpreted by @ref UpdateCodecState and that
+	routine may read additional information from the bitstream.
+
+	If the value is the length of the payload then it encodes the number
+	of bytes in the segment payload, not counting the segment header.
+*/
+TAGVALUE GetSegment(BITSTREAM *stream)
+{
+	TAGVALUE segment;
+	segment.tuple.tag = (TAGWORD)GetBits(stream, 16);
+	segment.tuple.value = (TAGWORD)GetBits(stream, 16);
+	return segment;
+}
+
+/*!
+	@brief Read the specified tag from the bitstream and return the value
+*/
+TAGWORD GetValue(BITSTREAM *stream, int tag)
+{
+	TAGVALUE segment = GetTagValue(stream);
+
+	assert(stream->error == BITSTREAM_ERROR_OKAY);
+	if (stream->error == BITSTREAM_ERROR_OKAY) {
+		assert(segment.tuple.tag == tag);
+		if (segment.tuple.tag == tag) {
+			return segment.tuple.value;
+		}
+		else {
+			stream->error = BITSTREAM_ERROR_BADTAG;
+		}
+	}
+
+	// An error has occurred so return zero (error code was set above)
+	return 0;
+}
+
+/*!
+	@brief Read the next tag value pair from the bitstream
+*/
+TAGVALUE GetTagValue(BITSTREAM *stream)
+{
+	TAGVALUE segment = GetSegment(stream);
+	while (segment.tuple.tag < 0) {
+		segment = GetSegment(stream);
+	}
+
+	return segment;
+}
+
+/*!
+	@brief Return true if the tag is optional
+*/
+bool IsTagOptional(TAGWORD tag)
+{
+	return (tag < 0);
+}
+
+/*!
+	@brief Return true if the tag is required
+*/
+bool IsTagRequired(TAGWORD tag)
+{
+	return (tag >= 0);
+}
+
+/*!
+	@brief Return true if a valid tag read from the bitstream
+*/
+bool IsValidSegment(BITSTREAM *stream, TAGVALUE segment, TAGWORD tag)
+{
+	return (stream->error == BITSTREAM_ERROR_OKAY &&
+			segment.tuple.tag == tag);
+}
+
+/*!
+	@brief Return true if the tag value pair has the specified tag and value
+*/
+bool IsTagValue(TAGVALUE segment, int tag, TAGWORD value)
+{
+	return (segment.tuple.tag == tag && segment.tuple.value == value);
+}