Enable same buffer for in and out on ARM A-32 (GH #683)

1 files changed, 14 insertions, 13 deletions

diff --git a/strciphr.cpp b/strciphr.cpp
index 7d33af15..b84f2c60 100644
--- a/strciphr.cpp
+++ b/strciphr.cpp
@@ -203,12 +203,18 @@ void CFB_CipherTemplate<BASE>::ProcessData(byte *outString, const byte *inString
 	//

 	//       Also see https://github.com/weidai11/cryptopp/issues/683.

 	//

-#if !defined(__arm__)

-	unsigned int alignment = policy.GetAlignment();

-	if (policy.CanIterate() && length >= bytesPerIteration && IsAlignedOn(outString, alignment))

+	// UPDATE: It appears the issue is related to alignment checks. When we made

+	//       the alignment check result volatile GCC and Clang stopped

+	//       short-circuiting the transform, which is what we wanted. I suspect

+	//       there's a little more to the issue, but we can enable the block again.

+

+	const unsigned int alignment = policy.GetAlignment();

+	volatile bool isAligned = IsAlignedOn(outString, alignment);

+	if (policy.CanIterate() && length >= bytesPerIteration && isAligned)

 	{

+		isAligned &= IsAlignedOn(inString, alignment);

 		const CipherDir cipherDir = GetCipherDir(*this);

-		if (IsAlignedOn(inString, alignment))

+		if (isAligned)

 			policy.Iterate(outString, inString, cipherDir, length / bytesPerIteration);

 		else

 		{

@@ -226,11 +232,6 @@ void CFB_CipherTemplate<BASE>::ProcessData(byte *outString, const byte *inString
 			// to use ptrdiff_t when subtracting pointers. We believe the relevant code paths

 			// are clean.

 			//

-			// There are two remaining open questions. The first is aliasing rules. Char-types

-			// are not bound by aliasing rules so we are OK. The second is array const-ness.

-			// The arrays are created in datatest.cpp and they are non-const. Since the original

-			// objects are non-const we are OK casting const-ness away as buffers are twiddled.

-			//

 			// One workaround is a distinct and aligned temporary buffer. It [mostly] works

 			// as expected but requires an extra allocation (casts not shown):

 			//

@@ -241,11 +242,11 @@ void CFB_CipherTemplate<BASE>::ProcessData(byte *outString, const byte *inString
 			memcpy(outString, inString, length);

 			policy.Iterate(outString, outString, cipherDir, length / bytesPerIteration);

 		}

-		inString = PtrAdd(inString, length - length % bytesPerIteration);

-		outString = PtrAdd(outString, length - length % bytesPerIteration);

-		length %= bytesPerIteration;

+		const size_t remainder = length % bytesPerIteration;

+		inString = PtrAdd(inString, length - remainder);

+		outString = PtrAdd(outString, length - remainder);

+		length = remainder;

 	}

-#endif

 

 	while (length >= bytesPerIteration)

 	{