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Trim the fat off SkPMFloat bench.

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This bench was ~75% overhead, ~25% good bench.  It is now just about the
opposite: about 30% of the runtime is loop and random number overhead, and
about 70% of the time is spent doing SkPMColor <-> SkPMFloat work.

BUG=skia:

NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/968133005
This commit is contained in:
mtklein 2015-03-03 08:03:27 -08:00 committed by Commit bot
parent 60d2a32b2d
commit 60ff4582ae
1 changed files with 23 additions and 4 deletions
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27
bench/PMFloatBench.cpp
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@ -1,6 +1,16 @@
#include "Benchmark.h"
#include "SkPMFloat.h"
#include "SkRandom.h"
// Used to prevent the compiler from optimizing away the whole loop.
volatile uint32_t blackhole = 0;
// Not a great random number generator, but it's very fast.
// The code we're measuring is quite fast, so low overhead is essential.
static uint32_t lcg_rand(uint32_t* seed) {
*seed *= 1664525;
*seed += 1013904223;
return *seed;
}
struct PMFloatBench : public Benchmark {
explicit PMFloatBench(bool clamp) : fClamp(clamp) {}
@ -9,14 +19,23 @@ struct PMFloatBench : public Benchmark {
bool isSuitableFor(Backend backend) SK_OVERRIDE { return backend == kNonRendering_Backend; }
void onDraw(const int loops, SkCanvas* canvas) SK_OVERRIDE {
SkRandom rand;
// Unlike blackhole, junk can and probably will be a register.
uint32_t junk = 0;
uint32_t seed = 0;
for (int i = 0; i < loops; i++) {
SkPMColor c = SkPreMultiplyColor(rand.nextU());
#ifdef SK_DEBUG
// Our SkASSERTs will remind us that it's technically required that we premultiply.
SkPMColor c = SkPreMultiplyColor(lcg_rand(&seed));
#else
// But it's a lot faster not to, and this code won't really mind the non-PM colors.
SkPMColor c = lcg_rand(&seed);
#endif
SkPMFloat pmf;
pmf.set(c);
SkPMColor back = fClamp ? pmf.clamped() : pmf.get();
if (c != back) { SkFAIL("no joy"); } // This conditional makes this not compile away.
junk ^= back;
}
blackhole ^= junk;
}
bool fClamp;