Branchless sorting network for a 6 element array

sort6-branchless.c

/**
 * Swap two positive 32-bit integers, to sorted order (ascending).
 *
 * @param   int32_t a
 * @param   int32_t b
 * @return  int32_t
 **/
static inline void _pswap32a(int32_t *input, size_t i1, size_t i2)
{
    int32_t a, b, c1, c2,
            v1 = input[i1],
            v2 = input[i2];

    // Subtract value2 from value1, and grab sign bit.
    c1 = (v1 - v2) >> 31 & 1;

    // Inverse of sign bit.
    c2 = c1 ^ 1;

    // Calculate min of value1 and value2.
    a = (v1 * c1) + (v2 * c2);

    // Calculate max of value1 and value2.
    b = (v1 * c2) + (v2 * c1);

    // Swap.
    input[i1] = a;
    input[i2] = b;
}

/**
 * Sorting network, to sort an array of 6 elements. The swap function
 * this uses does not branch.
 *
 * @param   int32_t[6]
 */
void sort6(int32_t array[6])
{
    _pswap32a(array, 1, 2);
    _pswap32a(array, 0, 2);
    _pswap32a(array, 0, 1);
    _pswap32a(array, 4, 5);
    _pswap32a(array, 3, 5);
    _pswap32a(array, 3, 4);
    _pswap32a(array, 0, 3);
    _pswap32a(array, 1, 4);
    _pswap32a(array, 2, 5);
    _pswap32a(array, 2, 4);
    _pswap32a(array, 1, 3);
    _pswap32a(array, 2, 3);
}