Check for multiplication overflow in MSADPCM decodeSample

Check for multiplication overflow (using __builtin_mul_overflow
if available) in MSADPCM.cpp decodeSample and return an empty
decoded block if an error occurs.

This fixes the 00193-audiofile-signintoverflow-MSADPCM case of mpruett#41

libaudiofile/modules/BlockCodec.cpp

@@ -52,8 +52,9 @@ void BlockCodec::runPull()
 	// Decompress into m_outChunk.
 	for (int i=0; i<blocksRead; i++)
 	{
-		decodeBlock(static_cast<const uint8_t *>(m_inChunk->buffer) + i * m_bytesPerPacket,
-			static_cast<int16_t *>(m_outChunk->buffer) + i * m_framesPerPacket * m_track->f.channelCount);
+		if (decodeBlock(static_cast<const uint8_t *>(m_inChunk->buffer) + i * m_bytesPerPacket,
+			static_cast<int16_t *>(m_outChunk->buffer) + i * m_framesPerPacket * m_track->f.channelCount)==0)
+			break;
 
 		framesRead += m_framesPerPacket;
 	}

libaudiofile/modules/MSADPCM.cpp

@@ -101,24 +101,60 @@ static const int16_t adaptationTable[] =
 	768, 614, 512, 409, 307, 230, 230, 230
 };
 
+int firstBitSet(int x)
+{
+        int position=0;
+        while (x!=0)
+        {
+                x>>=1;
+                ++position;
+        }
+        return position;
+}
+
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+int multiplyCheckOverflow(int a, int b, int *result)
+{
+#if (defined __GNUC__ && __GNUC__ >= 5) || ( __clang__ && __has_builtin(__builtin_mul_overflow))
+	return __builtin_mul_overflow(a, b, result);
+#else
+	if (firstBitSet(a)+firstBitSet(b)>31) // int is signed, so we can't use 32 bits
+		return true;
+	*result = a * b;
+	return false;
+#endif
+}
+
+
 // Compute a linear PCM value from the given differential coded value.
 static int16_t decodeSample(ms_adpcm_state &state,
-	uint8_t code, const int16_t *coefficient)
+	uint8_t code, const int16_t *coefficient, bool *ok=NULL)
 {
 	int linearSample = (state.sample1 * coefficient[0] +
 		state.sample2 * coefficient[1]) >> 8;
+	int delta;
 
 	linearSample += ((code & 0x08) ? (code - 0x10) : code) * state.delta;
 
 	linearSample = clamp(linearSample, MIN_INT16, MAX_INT16);
 
-	int delta = (state.delta * adaptationTable[code]) >> 8;
+	if (multiplyCheckOverflow(state.delta, adaptationTable[code], &delta))
+	{
+                if (ok) *ok=false;
+		_af_error(AF_BAD_COMPRESSION, "Error decoding sample");
+		return 0;
+	}
+	delta >>= 8;
 	if (delta < 16)
 		delta = 16;
 
 	state.delta = delta;
 	state.sample2 = state.sample1;
 	state.sample1 = linearSample;
+	if (ok) *ok=true;
 
 	return static_cast<int16_t>(linearSample);
 }
@@ -212,13 +248,16 @@ int MSADPCM::decodeBlock(const uint8_t *encoded, int16_t *decoded)
 	{
 		uint8_t code;
 		int16_t newSample;
+		bool ok;
 
 		code = *encoded >> 4;
-		newSample = decodeSample(*state[0], code, coefficient[0]);
+		newSample = decodeSample(*state[0], code, coefficient[0], &ok);
+		if (!ok) return 0;
 		*decoded++ = newSample;
 
 		code = *encoded & 0x0f;
-		newSample = decodeSample(*state[1], code, coefficient[1]);
+		newSample = decodeSample(*state[1], code, coefficient[1], &ok);
+		if (!ok) return 0;
 		*decoded++ = newSample;
 
 		encoded++;