... but if Po is of an 8-bit type, then for example:

unsigned char Po;
#define ROR(a) (((a) >> 1) | ((a) << 7))
Po = ROR(0x45);

should do.

With a constant as "input parameter" this should evaluate to the "rotated" constant at compile time; however if you would attempt:

unsigned char x,y;
[some code assigning a value to x]
y = ROR(x);

the efficiency of rotation would depend on the particular compiler's ability to
"decipher" this sort of expressions.

JW