On 5/17/19 9:47 AM, Richard Henderson wrote:
> first_equal = n;
> first_zero = n;
> for (i = n - 1; i >= 0; --i) {
> if (data1 == data2) {
> first_equal = i;
> }
> if (data1 == 0) {
> first_zero = i;
> }
> }
>
> // As an aside, there are bit tricks for the above,
> // but let's stay simple(r) for now.
What the hell, it's not /that/ tricky.
/*
* Returns a bit set in the MSB of each element that is zero,
* as defined by the mask M.
*/
static inline uint64_t zero_search(uint64_t a, uint64_t m)
{
return ~(((a & m) + m) | a | m);
}
/*
* Returns the byte offset for the first match, or 16 for no match.
*/
static inline int match_index(uint64_t c0, uint64_t c1)
{
return (c0 ? clz64(c0) : clz64(c1) + 64) >> 3;
}
Use
dup_const(MO_8, 0x7f)
dup_const(MO_16, 0x7fff)
dup_const(MO_32, 0x7fffffff)
for the M parameter for the different element sizes.
uint64_t a0, a1, b0, b1, e0, e1, z0, z1;
a0 = s390_vec_read_element64(v2, 0);
a1 = s390_vec_read_element64(v2, 1);
b0 = s390_vec_read_element64(v3, 0);
b1 = s390_vec_read_element64(v3, 1);
e0 = zero_search(a0 ^ b0, m);
e1 = zero_search(a1 ^ b1, m);
first_equal = match_index(e0, e1);
if (zs) {
z0 = zero_search(a0, m);
z1 = zero_search(a1, m);
first_zero = match_index(z0, z1);
...
r~
