2.4.1 Function Definition Example

A function called `med3' and selecting the median value over its three real argument values may be defined as:

const struct x1f4_function_type med3 = {
    "med3",
    median3,
    X1f4_E4_REAL,
    real3,
    3,
    0,
    4
};

See struct x1f4_function_type.

The name field of the function definition specifies the name of the function: `med3'.

The function field selects the routine performing the function logic, a certain median3 function.

The type field specifies that the function return type is real, hence it translates X1f4_E4_REAL.

See Symbolic Types.

The args field specifies the types of the function arguments and is assumed defined as:

int real3[] = { X1f4_E4_REAL, X1f4_E4_REAL, X1f4_E4_REAL };

The count field specifies the number of function arguments: 3.

The flags field specifies pretty much nothing in this function definition, hence is 0.

The length field specifies the function name length, 4.

The median3 function realizes the median over a set of three, i.e. it selects the value that is neither the smallest, neither the biggest.

int
median3(void *context, void *output, void **input)
{
    X1f4_E4_REAL a, b, c, o, *out;

    a = *(X1f4_E4_REAL *) input[0];
    b = *(X1f4_E4_REAL *) input[1];
    c = *(X1f4_E4_REAL *) input[2];

    if (a < b) {
	if (b < c) {
	    o = b;
	} else {
	    if (a < c) {
		o = c;
	    } else {
		o = a;
	    }
	}
    } else {
	if (a < c) {
	    o = a;
	} else {
	    if (b < c) {
		o = c;
	    } else {
		o = b;
	    }
	}
    }

    out = output;
    *out = o;

    return 0;
}

The median3 function reads its logic arguments from the addresses specified by input. Conversely, the computed value is stored at the address specified by output. The return 0 value marks successful execution.