Add float-to-half (binary16) conversion functions.

tests/MathTest.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorPriv.h"
 #include "SkEndian.h"
 #include "SkFloatBits.h"
 #include "SkFloatingPoint.h"
+#include "SkHalf.h"
 #include "SkMathPriv.h"
 #include "SkPoint.h"
 #include "SkRandom.h"
 #include "Test.h"
 
 static void test_clz(skiatest::Reporter* reporter) {
     REPORTER_ASSERT(reporter, 32 == SkCLZ(0));
     REPORTER_ASSERT(reporter, 31 == SkCLZ(1));
     REPORTER_ASSERT(reporter, 1 == SkCLZ(1 << 30));
     REPORTER_ASSERT(reporter, 0 == SkCLZ(~0U));
@@ skipping 297 matching lines @@
     REPORTER_ASSERT(reporter, !SkScalarIsNaN(big));
     REPORTER_ASSERT(reporter, !SkScalarIsNaN(-big));
     REPORTER_ASSERT(reporter, !SkScalarIsNaN(0));
 
     REPORTER_ASSERT(reporter, !SkScalarIsFinite(nan));
     REPORTER_ASSERT(reporter,  SkScalarIsFinite(big));
     REPORTER_ASSERT(reporter,  SkScalarIsFinite(-big));
     REPORTER_ASSERT(reporter,  SkScalarIsFinite(0));
 }
 
+static void unittest_half(skiatest::Reporter* reporter) {
+    static const float gFloats[] = {
+        0.f, 1.f, 0.5f, 0.499999f, 0.5000001f, 1.f/3,
+        -0.f, -1.f, -0.5f, -0.499999f, -0.5000001f, -1.f/3
+    };
+
+    for (size_t i = 0; i < SK_ARRAY_COUNT(gFloats); ++i) {
+        SkHalf h = SkFloatToHalf(gFloats[i]);
+        float f = SkHalfToFloat(h);
+        REPORTER_ASSERT(reporter, SkScalarNearlyEqual(f, gFloats[i]));
+    }
+
+    // check some special values
+    union FloatUnion {
+        uint32_t fU;
+        float    fF;
+    };
+
+    static const FloatUnion largestPositiveHalf = { ((142 << 23) | (1023 << 13)) };
+    SkHalf h = SkFloatToHalf(largestPositiveHalf.fF);
+    float f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(f, largestPositiveHalf.fF));
+
+    static const FloatUnion largestNegativeHalf = { (1u << 31) | (142u << 23) | (1023u << 13) };
+    h = SkFloatToHalf(largestNegativeHalf.fF);
+    f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(f, largestNegativeHalf.fF));
+
+    static const FloatUnion smallestPositiveHalf = { 102 << 23 };
+    h = SkFloatToHalf(smallestPositiveHalf.fF);
+    f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(f, smallestPositiveHalf.fF));
+
+    static const FloatUnion overflowHalf = { ((143 << 23) | (1023 << 13)) };
+    h = SkFloatToHalf(overflowHalf.fF);
+    f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, !SkScalarIsFinite(f) );
+
+    static const FloatUnion underflowHalf = { 101 << 23 };
+    h = SkFloatToHalf(underflowHalf.fF);
+    f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, f == 0.0f );
+
+    static const FloatUnion inf32 = { 255 << 23 };
+    h = SkFloatToHalf(inf32.fF);
+    f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, !SkScalarIsFinite(f) );
+
+    static const FloatUnion nan32 = { 255 << 23 | 1 };
+    h = SkFloatToHalf(nan32.fF);
+    f = SkHalfToFloat(h);
+    REPORTER_ASSERT(reporter, SkScalarIsNaN(f) );
+
+}
+
 static void test_muldiv255(skiatest::Reporter* reporter) {
     for (int a = 0; a <= 255; a++) {
         for (int b = 0; b <= 255; b++) {
             int ab = a * b;
             float s = ab / 255.0f;
             int round = (int)floorf(s + 0.5f);
             int trunc = (int)floorf(s);
 
             int iround = SkMulDiv255Round(a, b);
             int itrunc = SkMulDiv255Trunc(a, b);
@@ skipping 118 matching lines @@
 
     {
         SkFixed result = SkFixedDiv(100, 100);
         REPORTER_ASSERT(reporter, result == SK_Fixed1);
         result = SkFixedDiv(1, SK_Fixed1);
         REPORTER_ASSERT(reporter, result == 1);
     }
 
     unittest_fastfloat(reporter);
     unittest_isfinite(reporter);
+    unittest_half(reporter);
 
     for (i = 0; i < 10000; i++) {
         SkFixed numer = rand.nextS();
         SkFixed denom = rand.nextS();
         SkFixed result = SkFixedDiv(numer, denom);
         int64_t check = ((int64_t)numer << 16) / denom;
 
         (void)SkCLZ(numer);
         (void)SkCLZ(denom);
 
@@ skipping 117 matching lines @@
     test_divmod<int16_t>(r);
 }
 
 DEF_TEST(divmod_s32, r) {
     test_divmod<int32_t>(r);
 }
 
 DEF_TEST(divmod_s64, r) {
     test_divmod<int64_t>(r);
 }