#include "Benchmark.h"
#include "SkPMFloat.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) {}

    const char* onGetName() SK_OVERRIDE { return fClamp ? "SkPMFloat_clamp" : "SkPMFloat_get"; }
    bool isSuitableFor(Backend backend) SK_OVERRIDE { return backend == kNonRendering_Backend; }

    void onDraw(const int loops, SkCanvas* canvas) SK_OVERRIDE {
        // 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++) {
        #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();
            junk ^= back;
        }
        blackhole ^= junk;
    }

    bool fClamp;
};
DEF_BENCH(return new PMFloatBench( true);)
DEF_BENCH(return new PMFloatBench(false);)

#include "Benchmark.h"
#include "SkPMFloat.h"
#include "SkRandom.h"

struct PMFloatBench : public Benchmark {
    explicit PMFloatBench(bool clamp) : fClamp(clamp) {}

    const char* onGetName() SK_OVERRIDE { return fClamp ? "SkPMFloat_clamp" : "SkPMFloat_get"; }
    bool isSuitableFor(Backend backend) SK_OVERRIDE { return backend == kNonRendering_Backend; }

    void onDraw(const int loops, SkCanvas* canvas) SK_OVERRIDE {
        SkRandom rand;
        for (int i = 0; i < loops; i++) {
            SkPMColor c = SkPreMultiplyColor(rand.nextU());
            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.
        }
    }

    bool fClamp;
};
DEF_BENCH(return new PMFloatBench( true);)
DEF_BENCH(return new PMFloatBench(false);)

--- 
+++ 
@@ -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;
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
