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Add MandatoryBlockSize to last block test 

CC optimizes things best when isSpecial uses the two predicates. If the 'm_cipher.MandatoryBlockSize() > 0' is removed, then some block ciphers and modes lose up to 0.2 cpb. Apparently GCC can optimize away the second predicate easier than the first predicate.
pull/484/merge
Jeffrey Walton 2017-10-03 15:46:51 -04:00
parent aaeda3a57d
commit 84390ee1e1
No known key found for this signature in database
GPG Key ID: B36AB348921B1838
1 changed files with 32 additions and 18 deletions
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50
filters.cpp
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@ -687,15 +687,18 @@ void StreamTransformationFilter::LastPut(const byte *inString, size_t length)
{
byte *space = NULLPTR;
#if 1
// This block is new to StreamTransformationFilter. It somewhat of a hack and was added
// for OCB mode; see GitHub Issue 515. The rub with OCB is, its a block cipher and the
// last block size can be 0. However, its not the 0 predacted in the original code. In
// the orginal code 0 means "nothing special" so DEFAULT_PADDING is applied. OCB's 0
// literally means a final block size can be 0 or non-0; and no padding is needed in
// either case because OCB has its own scheme (see handling of P_* and A_*).
// last block size can be 0. However, "last block = 0" is not the 0 predacted in the
// original code. In the orginal code 0 means "nothing special" so DEFAULT_PADDING is
// applied. OCB's 0 literally means a final block size can be 0 or non-0; and no padding
// is needed in either case because OCB has its own scheme (see handling of P_* and A_*).
// Stream ciphers have policy objects to convey how to operate the cipher. The Crypto++
// framework operates well when MinLastBlockSize() is 1. However, it did not appear to
// cover the OCB case either because we can't stream OCB. It needs full block sizes.
// cover the OCB case either because we can't stream OCB. It needs full block sizes. In
// response we hacked a IsLastBlockSpecial(). When true StreamTransformationFilter
// defers to the mode for processing of the last block.
// The behavior supplied when IsLastBlockSpecial() will likely have to evolve to capture
// more complex beahviors of different authenc modes. I suspect it will have to change
// from a simple bool to something that conveys more information, like "last block
@ -704,33 +707,44 @@ void StreamTransformationFilter::LastPut(const byte *inString, size_t length)
// calculates the checksum on the cipher text at the same time, so we don't need the
// disjoint behavior of calling "EncryptBlock" followed by a separate "AuthenticateBlock".
// Additional information may allow us to avoid the two spearate calls.
if (m_cipher.IsLastBlockSpecial() && m_cipher.MandatoryBlockSize() > 1)
// Finally, GCC optimizes things best when isSpecial uses the two predicates. If the
// 'm_cipher.MandatoryBlockSize() > 0' is removed, then some block ciphers and modes
// lose up to 0.2 cpb. Apparently GCC can optimize away the second predicate easier
// than the first predicate.
const bool isSpecial = m_cipher.IsLastBlockSpecial() && m_cipher.MandatoryBlockSize() != 0;
if (isSpecial)
{
const size_t blocks = length / m_cipher.MandatoryBlockSize();
if (blocks != 0)
const size_t mandatoryBlockSize = m_cipher.MandatoryBlockSize();
const size_t optimalBlockSize = m_cipher.OptimalBlockSize();
const size_t leftOver = length % mandatoryBlockSize;
const size_t minReserve = STDMAX(2*mandatoryBlockSize, optimalBlockSize) + leftOver;
space = HelpCreatePutSpace(*AttachedTransformation(), DEFAULT_CHANNEL, mandatoryBlockSize, minReserve);
length -= leftOver;
if (length)
{
size_t blength = blocks * m_cipher.MandatoryBlockSize();
space = HelpCreatePutSpace(*AttachedTransformation(), DEFAULT_CHANNEL, blength, m_cipher.OptimalBlockSize());
m_cipher.ProcessData(space, inString, blength);
AttachedTransformation()->Put(space, blength);
// Process full blocks
m_cipher.ProcessData(space, inString, length);
AttachedTransformation()->Put(space, length);
inString += length;
}
const size_t leftover = length % m_cipher.MandatoryBlockSize();
const size_t reserve = 2*m_cipher.MandatoryBlockSize();
space = space ? space: HelpCreatePutSpace(*AttachedTransformation(), DEFAULT_CHANNEL, leftover+reserve);
if (leftover)
if (leftOver)
{
length = m_cipher.ProcessLastBlock(space, leftover+reserve, inString, leftover);
// Process final partial block
length = m_cipher.ProcessLastBlock(space, minReserve, inString, leftOver);
AttachedTransformation()->Put(space, length);
}
else
{
length = m_cipher.ProcessLastBlock(space, leftover+reserve, NULLPTR, 0);
// Process final empty block
length = m_cipher.ProcessLastBlock(space, minReserve, NULLPTR, 0);
AttachedTransformation()->Put(space, length);
}
return;
}
#endif
switch (m_padding)
{