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improve performances comparing image pixels

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This patch contains a bit of small optimizations.
It avoid boolean	 operations which could involve branches replacing
with binary operations (equal/all_ident -> some_differences).
The other optimization avoids the use of ABS. First the way the macro
was used (with a large expression) was not easy to optimize by the
compiler.
Then instead of using ABS a much simpler range check is used so instead
of (ABS(n) >= k) a ((n) <= -k || (n) >= k) is used. This looks small
but modern compilers can translate this not in range check in a couple
of machine instructions (and a single compare).

Using operf on same samples (using spice-server-replay) and trying 2 runs
I got

run             1       2
-------------------------
before    104441   106267
after      92387    91083

So the performance increase is about 13%.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Jonathon Jongsma <jjongsma@redhat.com>
This commit is contained in:
Frediano Ziglio 2015-09-04 11:00:18 +01:00
parent 39be1c448c
commit 1804b8bb85
1 changed files with 23 additions and 24 deletions
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47
server/red_bitmap_utils.h
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@ -49,6 +49,7 @@
#else
#define CONTRAST_TH 8
#endif
#define CONTRASTING(n) ((n) <= -CONTRAST_TH || (n) >= CONTRAST_TH)
#define SAMPLE_JUMP 15
@ -62,29 +63,27 @@ static const double FNAME(PIX_PAIR_SCORE)[] = {
// return 0 - equal, 1 - for contrast, 2 for no contrast (PIX_PAIR_SCORE is defined accordingly)
static inline int FNAME(pixelcmp)(PIXEL p1, PIXEL p2)
{
int diff = ABS(GET_r(p1) - GET_r(p2));
int equal;
int diff, any_different;
if (diff >= CONTRAST_TH) {
return 1;
}
equal = !diff;
diff = ABS(GET_g(p1) - GET_g(p2));
if (diff >= CONTRAST_TH) {
diff = GET_r(p1) - GET_r(p2);
any_different = diff;
if (CONTRASTING(diff)) {
return 1;
}
equal = equal && !diff;
diff = ABS(GET_b(p1) - GET_b(p2));
if (diff >= CONTRAST_TH) {
diff = GET_g(p1) - GET_g(p2);
any_different |= diff;
if (CONTRASTING(diff)) {
return 1;
}
equal = equal && !diff;
if (equal) {
diff = GET_b(p1) - GET_b(p2);
any_different |= diff;
if (CONTRASTING(diff)) {
return 1;
}
if (!any_different) {
return 0;
} else {
return 2;
@ -93,22 +92,22 @@ static inline int FNAME(pixelcmp)(PIXEL p1, PIXEL p2)
static inline double FNAME(pixels_square_score)(PIXEL *line1, PIXEL *line2)
{
double ret = 0.0;
int all_ident = TRUE;
double ret;
int any_different = 0;
int cmp_res;
cmp_res = FNAME(pixelcmp)(*line1, line1[1]);
all_ident = all_ident && (!cmp_res);
ret += FNAME(PIX_PAIR_SCORE)[cmp_res];
any_different |= cmp_res;
ret = FNAME(PIX_PAIR_SCORE)[cmp_res];
cmp_res = FNAME(pixelcmp)(*line1, *line2);
all_ident = all_ident && (!cmp_res);
any_different |= cmp_res;
ret += FNAME(PIX_PAIR_SCORE)[cmp_res];
cmp_res = FNAME(pixelcmp)(*line1, line2[1]);
all_ident = all_ident && (!cmp_res);
any_different |= cmp_res;
ret += FNAME(PIX_PAIR_SCORE)[cmp_res];
// ignore squares where all pixels are identical
if (all_ident) {
ret -= (FNAME(PIX_PAIR_SCORE)[0]) * 3;
if (!any_different) {
ret = 0;
}
return ret;