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

src/core/SkHalf.h

Index: src/core/SkHalf.h
diff --git a/src/core/SkHalf.h b/src/core/SkHalf.h
new file mode 100644
index 0000000000000000000000000000000000000000..3fd07793e9bfb59398dbac6651c7267e18dd6b2d
--- /dev/null
+++ b/src/core/SkHalf.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkHalf_DEFINED
+#define SkHalf_DEFINED
+
+#include "SkTypes.h"
+
+// 16-bit floating point value
+// format is 1 bit sign, 5 bits exponent, 10 bits mantissa
+// only used for storage
+typedef uint16_t SkHalf;
+
+// convert between half and single precision floating point
+float SkHalfToFloat(SkHalf h);
+SkHalf SkFloatToHalf(float f);
+
+#endif