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Avoid overreads in the bitstream reader

This commit is contained in:
Martin Storsjo 2018-09-01 00:18:58 +03:00
parent 36a85bf987
commit 3aa26e273e
1 changed files with 20 additions and 7 deletions
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27
libFDK/include/FDK_bitstream.h
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@ -196,6 +196,23 @@ FDK_INLINE void FDKdeleteBitStream(HANDLE_FDK_BITSTREAM hBitStream) {
FDKfree(hBitStream);
}
FDK_INLINE void FDKrefillCache(HANDLE_FDK_BITSTREAM hBitStream,
INT missingBits) {
INT validBits = FDK_getValidBits(&hBitStream->hBitBuf);
if (validBits >= CACHE_BITS) {
hBitStream->CacheWord = FDK_get32(&hBitStream->hBitBuf);
hBitStream->BitsInCache += CACHE_BITS;
return;
}
hBitStream->CacheWord <<= validBits;
hBitStream->CacheWord |= FDK_get(&hBitStream->hBitBuf, validBits);
hBitStream->BitsInCache += validBits;
if (missingBits > validBits) {
hBitStream->CacheWord <<= missingBits - validBits;
hBitStream->BitsInCache += missingBits - validBits;
}
}
/**
* \brief ReadBits Function (forward). This function returns a number of
* sequential bits from the input bitstream.
@ -215,8 +232,7 @@ FDK_INLINE UINT FDKreadBits(HANDLE_FDK_BITSTREAM hBitStream,
FDK_ASSERT(numberOfBits <= 32);
if (missingBits > 0) {
if (missingBits != 32) bits = hBitStream->CacheWord << missingBits;
hBitStream->CacheWord = FDK_get32(&hBitStream->hBitBuf);
hBitStream->BitsInCache += CACHE_BITS;
FDKrefillCache(hBitStream, missingBits);
}
hBitStream->BitsInCache -= numberOfBits;
@ -227,9 +243,7 @@ FDK_INLINE UINT FDKreadBits(HANDLE_FDK_BITSTREAM hBitStream,
FDK_INLINE UINT FDKreadBit(HANDLE_FDK_BITSTREAM hBitStream) {
if (!hBitStream->BitsInCache) {
hBitStream->CacheWord = FDK_get32(&hBitStream->hBitBuf);
hBitStream->BitsInCache = CACHE_BITS - 1;
return hBitStream->CacheWord >> 31;
FDKrefillCache(hBitStream, 1);
}
hBitStream->BitsInCache--;
@ -254,8 +268,7 @@ FDK_INLINE UINT FDKread2Bits(HANDLE_FDK_BITSTREAM hBitStream) {
INT missingBits = 2 - (INT)hBitStream->BitsInCache;
if (missingBits > 0) {
bits = hBitStream->CacheWord << missingBits;
hBitStream->CacheWord = FDK_get32(&hBitStream->hBitBuf);
hBitStream->BitsInCache += CACHE_BITS;
FDKrefillCache(hBitStream, 2);
}
hBitStream->BitsInCache -= 2;