elma
and elmc
are both unsigned long
arrays. So are res1
and res2
.
unsigned long simdstore[2];
__m128i *p, simda, simdb, simdc;
p = (__m128i *) simdstore;
for (i = 0; i < _polylen; i++)
{
u1 = (elma[i] >> l) & 15;
u2 = (elmc[i] >> l) & 15;
for (k = 0; k < 20; k++)
{
//res1[i + k] ^= _mulpre1[u1][k];
//res2[i + k] ^= _mulpre2[u2][k];
simda = _mm_set_epi64x (_mulpre2[u2][k], _mulpre1[u1][k]);
simdb = _mm_set_epi64x (res2[i + k], res1[i + k]);
simdc = _mm_xor_si128 (simda, simdb);
_mm_store_si128 (p, simdc);
res1[i + k] = simdstore[0];
res2[i + k] = simdstore[1];
}
}
Within the for loop is included both the non-simd and simd version of XOR of elements. First two lines within the second for loop do the explicit XOR, whereas the rest implements the simd version of the same operation.
This loop is called from outside hundreds of times, so optimizing this loop will help bring down the total computation time.
The problem is simd code runs many times slower than the scalar code.
EDIT: Done partial unrolling
__m128i *p1, *p2, *p3, *p4;
p1 = (__m128i *) simdstore1;
p2 = (__m128i *) simdstore2;
p3 = (__m128i *) simdstore3;
p4 = (__m128i *) simdstore4;
for (i = 0; i < 20; i++)
{
u1 = (elma[i] >> l) & 15;
u2 = (elmc[i] >> l) & 15;
for (k = 0; k < 20; k = k + 4)
{
simda1 = _mm_set_epi64x (_mulpre2[u2][k], _mulpre1[u1][k]);
simda2 = _mm_set_epi64x (_mulpre2[u2][k + 1], _mulpre1[u1][k + 1]);
simda3 = _mm_set_epi64x (_mulpre2[u2][k + 2], _mulpre1[u1][k + 2]);
simda4 = _mm_set_epi64x (_mulpre2[u2][k + 3], _mulpre1[u1][k + 3]);
simdb1 = _mm_set_epi64x (res2[i + k], res1[i + k]);
simdb2 = _mm_set_epi64x (res2[i + k + 1], res1[i + k + 1]);
simdb3 = _mm_set_epi64x (res2[i + k + 2], res1[i + k + 2]);
simdb4 = _mm_set_epi64x (res2[i + k + 3], res1[i + k + 3]);
simdc1 = _mm_xor_si128 (simda1, simdb1);
simdc2 = _mm_xor_si128 (simda2, simdb2);
simdc3 = _mm_xor_si128 (simda3, simdb3);
simdc4 = _mm_xor_si128 (simda4, simdb4);
_mm_store_si128 (p1, simdc1);
_mm_store_si128 (p2, simdc2);
_mm_store_si128 (p3, simdc3);
_mm_store_si128 (p4, simdc4);
res1[i + k]= simdstore1[0];
res2[i + k]= simdstore1[1];
res1[i + k + 1]= simdstore2[0];
res2[i + k + 1]= simdstore2[1];
res1[i + k + 2]= simdstore3[0];
res2[i + k + 2]= simdstore3[1];
res1[i + k + 3]= simdstore4[0];
res2[i + k + 3]= simdstore4[1];
}
}
But, the result does not change much; it still takes twice as long as scalar code.