Invalid C++ Code Prevents Compilation With Clang (Bug #3191)

The file dpstereo.cpp contains some invalid C++ code and will not compile on newer versions of Clang. Although most compilers will not flag the error, the code is clearly not correct.

The specific problem occurs when the macros

#define CV_IMAX3(a,b,c) ((temp3 = (a) >= (b) ? (a) : (b)),(temp3 >= (c) ? temp3 : (c)))
#define CV_IMIN3(a,b,c) ((temp3 = (a) <= (b) ? (a) : (b)),(temp3 <= (c) ? temp3 : (c)))

are used in expressions like

CV_IMAX3( srcdata1[j-3], srcdata1[j-2], srcdata1[j-1] ) - CV_IMIN3( srcdata1[j-3], srcdata1[j-2], srcdata1[j-1] )

Macros do not have local variables, and CV_IMIN3 and CV_IMAX3 both use the variable temp3. Because the subtraction of primitive types does not establish a sequenced-before relation, the expressions substituted for CV_IMIN3 and CV_IMAX3 can be evaluated in either order. This would allow temp3 to be assigned different values depending on how the compiler evaluated the expression. To prevent this problem, C++ prohibits this "unsequenced" assignment.