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libweston: Optimise matrix multiplication

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The previous version used div() to separate the column and row of the
current element, but that function is implemented as a libc call, which
prevented the compiler from vectorising the loop and made matrix
multiplication appear quite high in profiles.

With div() removed, we are down from 64 calls to vfmadd132ss acting on
one float at a time, to just 8 calls to vfmadd132ps when compiled with
AVX2 support (or 16 mulps, 16 addps with SSE2 support only), and the
function isn’t a hot spot any more.

Signed-off-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
This commit is contained in:
Emmanuel Gil Peyrot 2023-01-02 17:46:18 +01:00 committed by Derek Foreman
parent 102acac6a9
commit e13c99690b
1 changed files with 9 additions and 9 deletions
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18
shared/matrix.c
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@ -61,16 +61,16 @@ weston_matrix_multiply(struct weston_matrix *m, const struct weston_matrix *n)
{
struct weston_matrix tmp;
const float *row, *column;
div_t d;
int i, j;
int i, j, k;
for (i = 0; i < 16; i++) {
tmp.d[i] = 0;
d = div(i, 4);
row = m->d + d.quot * 4;
column = n->d + d.rem;
for (j = 0; j < 4; j++)
tmp.d[i] += row[j] * column[j * 4];
for (i = 0; i < 4; i++) {
row = m->d + i * 4;
for (j = 0; j < 4; j++) {
tmp.d[4 * i + j] = 0;
column = n->d + j;
for (k = 0; k < 4; k++)
tmp.d[4 * i + j] += row[k] * column[k * 4];
}
}
tmp.type = m->type | n->type;
memcpy(m, &tmp, sizeof tmp);