Create FP16 LUTs when needed

ui/gfx/half_float_unittest.cc

+// Copyright (c) 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <math.h>
+
+#include "base/macros.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "ui/gfx/half_float.h"
+
+namespace gfx {
+
+class HalfFloatTest : public testing::Test {
+ public:
+  union FloatUIntUnion {
+    // this must come first for the initializations below to work
+    uint32_t fUInt;
+    float fFloat;
+  };
+
+  // Convert an IEEE 754 half-float to a float value
+  // that we can do math on.
+  float FromHalfFloat(HalfFloat half_float) {
+    int sign = (half_float & 0x8000) ? -1 : 1;
+    int exponent = (half_float >> 10) & 0x1F;
+    int fraction = half_float & 0x3FF;
+    if (exponent == 0) {
+      return powf(2.0f, -24.0f) * fraction;
+    } else if (exponent == 0x1F) {
+      return sign * 1000000000000.0f;
+    } else {
+      return pow(2.0f, exponent - 25) * (0x400 + fraction);
+    }
+  }
+
+  HalfFloat ConvertTruth(float f) {
+    if (f < 0.0)
+      return 0x8000 | ConvertTruth(-f);
+    int max = 0x8000;
+    int min = 0;
+    while (max - min > 1) {
+      int mid = (min + max) >> 1;
+      if (FromHalfFloat(mid) > f) {
+        max = mid;
+      } else {
+        min = mid;
+      }
+    }
+    float low = FromHalfFloat(min);
+    float high = FromHalfFloat(min + 1);
+    if (f - low <= high - f) {
+      return min;
+    } else {
+      return min + 1;
+    }
+  }
+
+  HalfFloat Convert(float f) {
+    HalfFloat ret;
+    FloatToHalfFloat(&f, &ret, 1);
+    return ret;
+  }
+};
+
+TEST_F(HalfFloatTest, NoCrashTest) {
+  Convert(nanf(""));
+  Convert(1.0E30f);
+  Convert(-1.0E30f);
+  Convert(1.0E-30f);
+  Convert(-1.0E-30f);
+}
+
+TEST_F(HalfFloatTest, SimpleTest) {
+  static float test[] = {
+      0.0f,    1.0f,    10.0f,    1000.0f,  65503.0f,
+      1.0E-3f, 1.0E-6f, 1.0E-20f, 1.0E-44f,
+  };
+  for (size_t i = 0; i < arraysize(test); i++) {
+    EXPECT_EQ(ConvertTruth(test[i]), Convert(test[i])) << " float = "
+                                                       << test[i];
+    if (test[i] != 0.0) {
+      EXPECT_EQ(ConvertTruth(-test[i]), Convert(-test[i])) << " float = "
+                                                           << -test[i];
+    }
+  }
+}
+
+}  // namespace