Templatize SkPMFloat to support both 1 and 255 biases.

bench/PMFloatBench.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #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;
 }
 
-// I'm having better luck getting these to constant-propagate away as template parameters.
+template <int kBias>
 struct PMFloatRoundtripBench : public Benchmark {
-    PMFloatRoundtripBench() {}
+    SkString fName;
+    PMFloatRoundtripBench() {
+        fName.appendf("SkPMFloat<%d>_roundtrip", kBias);
+    }
 
-    const char* onGetName() override { return "SkPMFloat_roundtrip"; }
+    const char* onGetName() override { return fName.c_str(); }
     bool isSuitableFor(Backend backend) override { return backend == kNonRendering_Backend; }
 
     void onDraw(const int loops, SkCanvas* canvas) 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++) {
+        for (int i = 0; i < 1000*loops; i++) {
             SkPMColor color;
         #ifdef SK_DEBUG
             // Our SkASSERTs will remind us that it's technically required that we premultiply.
             color = SkPreMultiplyColor(lcg_rand(&seed));
         #else
             // But it's a lot faster not to, and this code won't really mind the non-PM colors.
             color = lcg_rand(&seed);
         #endif
 
-            auto f = SkPMFloat::FromPMColor(color);
+            auto f = SkPMFloat<kBias>::FromPMColor(color);
             SkPMColor back = f.round();
             junk ^= back;
         }
         blackhole ^= junk;
     }
 };
-DEF_BENCH(return new PMFloatRoundtripBench;)
+DEF_BENCH(return new PMFloatRoundtripBench<1>;)
+DEF_BENCH(return new PMFloatRoundtripBench<255>;)
 
 struct PMFloatGradientBench : public Benchmark {
     const char* onGetName() override { return "PMFloat_gradient"; }
     bool isSuitableFor(Backend backend) override { return backend == kNonRendering_Backend; }
 
     SkPMColor fDevice[100];
     void onDraw(const int loops, SkCanvas*) override {
-        Sk4f c0 = SkPMFloat::FromARGB(1, 1, 0, 0),
-             c1 = SkPMFloat::FromARGB(1, 0, 0, 1),
+        Sk4f c0 = SkPMFloat<1>::FromARGB(1, 1, 0, 0),
+             c1 = SkPMFloat<1>::FromARGB(1, 0, 0, 1),
              dc = c1 - c0,
              fx(0.1f),
              dx(0.002f),
              dcdx(dc*dx),
              dcdx4(dcdx+dcdx+dcdx+dcdx);
 
         for (int n = 0; n < loops; n++) {
             Sk4f a = c0 + dc*fx,
                  b = a + dcdx,
                  c = b + dcdx,
                  d = c + dcdx;
             for (size_t i = 0; i < SK_ARRAY_COUNT(fDevice); i += 4) {
-                fDevice[i+0] = SkPMFloat(a).round();
-                fDevice[i+1] = SkPMFloat(b).round();
-                fDevice[i+2] = SkPMFloat(c).round();
-                fDevice[i+3] = SkPMFloat(d).round();
+                fDevice[i+0] = SkPMFloat<1>(a).round();
+                fDevice[i+1] = SkPMFloat<1>(b).round();
+                fDevice[i+2] = SkPMFloat<1>(c).round();
+                fDevice[i+3] = SkPMFloat<1>(d).round();
                 a = a + dcdx4;
                 b = b + dcdx4;
                 c = c + dcdx4;
                 d = d + dcdx4;
             }
         }
     }
 };
 
 DEF_BENCH(return new PMFloatGradientBench;)