On 1/26/2018 5:04 AM, Pavan Nikhilesh wrote:
> Currently, rte_reciprocal only supports unsigned 32bit divisors. This
> commit adds support for unsigned 64bit divisors.
>
> Signed-off-by: Pavan Nikhilesh <pbhagavat...@caviumnetworks.com>
<...>
> +static uint64_t
> +divide_128_div_64_to_64(uint64_t u1, uint64_t u0, uint64_t v, uint64_t *r)
> +{
> + const uint64_t b = (1ULL << 32); /* Number base (16 bits). */
> + uint64_t un1, un0, /* Norm. dividend LSD's. */
> + vn1, vn0, /* Norm. divisor digits. */
> + q1, q0, /* Quotient digits. */
> + un64, un21, un10, /* Dividend digit pairs. */
> + rhat; /* A remainder. */
> + int s; /* Shift amount for norm. */
> +
> + /* If overflow, set rem. to an impossible value. */
> + if (u1 >= v) {
> + if (r != NULL)
> + *r = (uint64_t) -1;
> + return (uint64_t) -1;
> + }
> +
> + /* Count leading zeros. */
> + s = __builtin_clzll(v);
> + if (s > 0) {
> + v = v << s;
> + un64 = (u1 << s) | ((u0 >> (64 - s)) & (-s >> 31));
Hi Pavan,
This is causing a cppcheck warning [1]. s is `int` and we know here s > 0,
so `-s >> 31` should be 0xffffffff right, what is the point of this operation
instead of using hardcoded value?
[1]
(error) Shifting signed 32-bit value by 31 bits is undefined behaviour
