One of the most common errors while porting from 32-bit Code to a 64-bit code is in the use of Math.h
Suppose you use a call to the pow function and get an error such as "Ambiguous call to a overloaded member function" in the 64-bit compiler. The reason is that a few more overloaded functions have been added to the math.h making it ambiguous for the compiler to understand which function to call. For example, pow now has seven overloads:
long double pow(long double,int)
long double pow(long double,long double)
The straightforward solution to this problem is to call the methods with the explicit parameter typecast. So the call now looks like:
... and so on and so forth.
Modifying your existing 32-bit code for explicit parameters works with both 32-bit and 64-bit code and helps make porting a bit less painful.