— Macro: GSL_IS_ODD (n)

This macro evaluates to 1 if n is odd and 0 if n is even. The argument n must be of integer type.

— Macro: GSL_IS_EVEN (n)

This macro is the opposite of GSL_IS_ODD(n). It evaluates to 1 if n is even and 0 if n is odd. The argument n must be of integer type.