Trim the fat off SkPMFloat bench.
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
diff --git a/bench/PMFloatBench.cpp b/bench/PMFloatBench.cpp
index 8250c9e..1f9c291 100644
--- a/bench/PMFloatBench.cpp
+++ b/bench/PMFloatBench.cpp
@@ -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 @@
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;
