Promote some value to an unsigned integer type

promote.h

/*
uint32_t a = (...);
uint32_t b = a << 31;

When uint32_t is defined as a short type, then both operands of the
shift will get promoted to int. Thus above code is then equivalent to:

unsigned short a = (...);
unsigned short b = (unsigned short)((int)a << 31);

THIS IS UNDEFINED BEHAVIOUR, though. (Shifting a negative value)

Solution: Promote to an unsigned type before shifting:

uint32_t b = PROMOTE_AT_LEAST_UNSIGNED(a) << 31;

Source: http://stackoverflow.com/q/39964651/1116364
*/
#define PROMOTE_AT_LEAST_UNSIGNED(x) ((x) + 0u)