Improve naive SkColorXform to half floats

tests/Float16Test.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #include "SkAutoPixmapStorage.h"
 #include "SkColor.h"
@@ skipping 55 matching lines @@
         float f = SkHalfToFloat(h);
         if (isfinite(f)) {
             float got = SkHalfToFloat_finite(h)[0];
             if (got != f) {
                 SkDebugf("0x%04x -> 0x%08x (%g), want 0x%08x (%g)\n",
                         h,
                         u(got), got,
                         u(f), f);
             }
             REPORTER_ASSERT(r, SkHalfToFloat_finite(h)[0] == f);
-            REPORTER_ASSERT(r, SkFloatToHalf_finite(SkHalfToFloat_finite(h)) == h);
+            uint64_t result;
+            SkFloatToHalf_finite(SkHalfToFloat_finite(h)).store(&result);
+            REPORTER_ASSERT(r, result == h);
         }
     }
 }
 
 DEF_TEST(FloatToHalf_finite, r) {
 #if 0
     for (uint64_t bits = 0; bits <= 0xffffffff; bits++) {
 #else
     SkRandom rand;
     for (int i = 0; i < 1000000; i++) {
         uint32_t bits = rand.nextU();
 #endif
         float f;
         memcpy(&f, &bits, 4);
         if (isfinite(f) && isfinite(SkHalfToFloat(SkFloatToHalf(f)))) {
-            uint16_t h1 = (uint16_t)SkFloatToHalf_finite(Sk4f(f,0,0,0)),
+            uint16_t h1 = SkFloatToHalf_finite(Sk4f(f,0,0,0))[0],
                      h2 = SkFloatToHalf(f);
             bool ok = (h1 == h2 || h1 == h2-1);
             REPORTER_ASSERT(r, ok);
             if (!ok) {
                 SkDebugf("%08x (%g) -> %04x, want %04x (%g)\n",
                          bits, f, h1, h2, SkHalfToFloat(h2));
                 break;
             }
         }
     }
 }