Subject: Fix sha256 assembly problem with signed address comparison.
Author: Ken Raeburn
Bug: http://sourceforge.net/apps/trac/cryptopp/ticket/2

A message straddling memory address 0x80000000 (e.g., starting at
0x7ffffff0 with length 32) on 32-bit x86 with the asm support enabled
gets hashed incorrectly, because signed comparisons are done on
addresses, so the ending address looks "less than" the starting
address.  (On some OSes, you can't get such an address range, or you
may need a special kernel configuration.)  It's probably safer to
assume that messages won't straddle address 0.

Index: libcrypto++/sha.cpp
===================================================================
--- libcrypto++.orig/sha.cpp	2010-06-15 23:26:51.000000000 +0200
+++ libcrypto++/sha.cpp	2010-06-15 23:28:31.000000000 +0200
@@ -374,7 +374,7 @@
 	AS2(	movdqa	[AS_REG_7+1*16], xmm1)
 	AS2(	movdqa	[AS_REG_7+0*16], xmm0)
 	AS2(	cmp		WORD_REG(dx), DATA_END)
-	ASJ(	jl,		0, b)
+	ASJ(	jb,		0, b)
 #endif
 
 #if CRYPTOPP_BOOL_X86
@@ -398,7 +398,7 @@
 	AS2(	add		[AS_REG_7+7*4], ecx)
 	AS2(	mov		ecx, AS_REG_7d)
 	AS2(	cmp		WORD_REG(dx), DATA_END)
-	ASJ(	jl,		2, b)
+	ASJ(	jb,		2, b)
 #if CRYPTOPP_BOOL_SSE2_ASM_AVAILABLE
 	ASL(5)
 #endif