stagefright: allow ABitReader to fail gracefully (3be85f90) · Commits · e / os / android_frameworks_av

include/media/stagefright/foundation/ABitReader.h

+24 −3

Original line number	Diff line number	Diff line
		@@ -30,23 +30,44 @@ public:
		ABitReader(const uint8_t *data, size_t size);
		virtual ~ABitReader();

		// Tries to get \|n\| bits. If not successful, returns \|fallback\|. Otherwise, returns result.
		// Reading 0 bits will always succeed and return 0.
		uint32_t getBitsWithFallback(size_t n, uint32_t fallback);

		// Tries to get \|n\| bits. If not successful, returns false. Otherwise, stores result in \|out\|
		// and returns true. Use !overRead() to determine if this call was successful. Reading 0 bits
		// will always succeed and write 0 in \|out\|.
		bool getBitsGraceful(size_t n, uint32_t *out);

		// Gets \|n\| bits and returns result. ABORTS if unsuccessful. Reading 0 bits will always
		// succeed.
		uint32_t getBits(size_t n);
		void skipBits(size_t n);

		// Tries to skip \|n\| bits. Returns true iff successful. Skipping 0 bits will always succeed.
		bool skipBits(size_t n);

		// "Puts" \|n\| bits with the value \|x\| back virtually into the bit stream. The put-back bits
		// are not actually written into the data, but are tracked in a separate buffer that can
		// store at most 32 bits. This is a no-op if the stream has already been over-read.
		void putBits(uint32_t x, size_t n);

		size_t numBitsLeft() const;

		const uint8_t *data() const;

		// Returns true iff the stream was over-read (e.g. any getBits operation has been unsuccessful
		// due to overread (and not trying to read >32 bits).)
		bool overRead() const { return mOverRead; }

		protected:
		const uint8_t *mData;
		size_t mSize;

		uint32_t mReservoir; // left-aligned bits
		size_t mNumBitsLeft;
		bool mOverRead;

		virtual void fillReservoir();
		virtual bool fillReservoir();

		DISALLOW_EVIL_CONSTRUCTORS(ABitReader);
		};
		@@ -60,7 +81,7 @@ public:
		private:
		int32_t mNumZeros;

		virtual void fillReservoir();
		virtual bool fillReservoir();

		DISALLOW_EVIL_CONSTRUCTORS(NALBitReader);
		};

media/libstagefright/foundation/ABitReader.cpp

+45 −11

Original line number	Diff line number	Diff line
		@@ -24,14 +24,18 @@ ABitReader::ABitReader(const uint8_t *data, size_t size)
		: mData(data),
		mSize(size),
		mReservoir(0),
		mNumBitsLeft(0) {
		mNumBitsLeft(0),
		mOverRead(false) {
		}

		ABitReader::~ABitReader() {
		}

		void ABitReader::fillReservoir() {
		CHECK_GT(mSize, 0u);
		bool ABitReader::fillReservoir() {
		if (mSize == 0) {
		mOverRead = true;
		return false;
		}

		mReservoir = 0;
		size_t i;
		@@ -44,15 +48,32 @@ void ABitReader::fillReservoir() {

		mNumBitsLeft = 8 * i;
		mReservoir <<= 32 - mNumBitsLeft;
		return true;
		}

		uint32_t ABitReader::getBits(size_t n) {
		CHECK_LE(n, 32u);
		uint32_t ret;
		CHECK(getBitsGraceful(n, &ret));
		return ret;
		}

		uint32_t ABitReader::getBitsWithFallback(size_t n, uint32_t fallback) {
		uint32_t ret = fallback;
		(void)getBitsGraceful(n, &ret);
		return ret;
		}

		bool ABitReader::getBitsGraceful(size_t n, uint32_t *out) {
		if (n > 32) {
		return false;
		}

		uint32_t result = 0;
		while (n > 0) {
		if (mNumBitsLeft == 0) {
		fillReservoir();
		if (!fillReservoir()) {
		return false;
		}
		}

		size_t m = n;
		@@ -67,21 +88,30 @@ uint32_t ABitReader::getBits(size_t n) {
		n -= m;
		}

		return result;
		*out = result;
		return true;
		}

		void ABitReader::skipBits(size_t n) {
		bool ABitReader::skipBits(size_t n) {
		uint32_t dummy;
		while (n > 32) {
		getBits(32);
		if (!getBitsGraceful(32, &dummy)) {
		return false;
		}
		n -= 32;
		}

		if (n > 0) {
		getBits(n);
		return getBitsGraceful(n, &dummy);
		}
		return true;
		}

		void ABitReader::putBits(uint32_t x, size_t n) {
		if (mOverRead) {
		return;
		}

		CHECK_LE(n, 32u);

		while (mNumBitsLeft + n > 32) {
		@@ -139,8 +169,11 @@ bool NALBitReader::atLeastNumBitsLeft(size_t n) const {
		return (numBitsRemaining <= 0);
		}

		void NALBitReader::fillReservoir() {
		CHECK_GT(mSize, 0u);
		bool NALBitReader::fillReservoir() {
		if (mSize == 0) {
		mOverRead = true;
		return false;
		}

		mReservoir = 0;
		size_t i = 0;
		@@ -165,6 +198,7 @@ void NALBitReader::fillReservoir() {

		mNumBitsLeft = 8 * i;
		mReservoir <<= 32 - mNumBitsLeft;
		return true;
		}

		} // namespace android