Several fixes for fp 16 rendering:

dm/DM.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "CrashHandler.h"
 #include "DMJsonWriter.h"
 #include "DMSrcSink.h"
@@ skipping 940 matching lines @@
         }
 
     } else if (bitmap.colorType() == kRGBA_F16_SkColorType) {
         // These are premul linear half-float pixels in RGBA order.
         // We want unpremul sRGB 8-bit pixels in RGBA order.  We'll get there via floats.
         bitmap.lockPixels();
         auto px = (const uint64_t*)bitmap.getPixels();
         if (!px) {
             return false;
         }
+        const Sk4f vecZero(0);
+        const Sk4f vecOne(1);
         for (int i = 0; i < w*h; i++) {
-            Sk4f fs = SkHalfToFloat_01(px[i]);    // Convert up to linear floats.

[mtklein, 2016/04/14 19:20:13]

FYI folks, I do intend to replace SkHalfToFloat_01() with
SkHalfToFloat_finite(), which should let us get back to something short here.

+            // Convert up to linear floats.
+            Sk4f fs(SkHalfToFloat(static_cast<SkHalf>(px[i] >> (0 * 16))),
+                    SkHalfToFloat(static_cast<SkHalf>(px[i] >> (1 * 16))),
+                    SkHalfToFloat(static_cast<SkHalf>(px[i] >> (2 * 16))),
+                    SkHalfToFloat(static_cast<SkHalf>(px[i] >> (3 * 16))));
+            fs = Sk4f::Min(Sk4f::Max(fs, vecZero), vecOne);  // Clamp

[mtklein, 2016/04/14 19:20:13]

I like to write this as

   fs = Sk4f::Max(0.0f, Sk4f::Min(fs, 1.0f));

It puts the value visually between its min and max.

(You can use scalars and literals with Sk4f.  I think even Sk4f::Max(0,
Sk4f::Min(fs, 1)) is fine here.)

             float invA = 1.0f / fs[3];
             fs = fs * Sk4f(invA, invA, invA, 1);  // Unpremultiply.
             rgba[i] = Sk4f_toS32(fs);             // Pack down to sRGB bytes.
         }
 
 
     } else {
         // We "should" gamma correct in here but we don't.
         // We want Gold to show exactly what our clients are seeing, broken gamma.
 
@@ skipping 492 matching lines @@
 #endif
 }
 } // namespace skiatest
 
 #if !defined(SK_BUILD_FOR_IOS)
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return dm_main();
 }
 #endif