start again on Sk4x with portable version and unit tests

src/core/Sk4x.h

Index: src/core/Sk4x.h
diff --git a/src/core/Sk4x.h b/src/core/Sk4x.h
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+++ b/src/core/Sk4x.h
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+#ifndef Sk4x_DEFINED
+#define Sk4x_DEFINED
+
+#include "SkTypes.h"
+
+#define SK4X_PREAMBLE 1
+    #include "Sk4x_portable.h"
+#undef SK4X_PREAMBLE
+
+template <typename T> class Sk4x;
+typedef Sk4x<float>   Sk4f;
+typedef Sk4x<int32_t> Sk4i;
+
+template <typename T> class Sk4x {
+public:
+    Sk4x();  // Uninitialized; use Sk4x(0,0,0,0) for zero.
+    Sk4x(T, T, T, T);
+
+    Sk4x(const Sk4x&);
+    Sk4x& operator=(const Sk4x&);
+
+    static Sk4x Load       (const T[4]);
+    static Sk4x LoadAligned(const T[4]);
+
+    void store       (T[4]) const;
+    void storeAligned(T[4]) const;
+
+    template <typename Dst> Dst reinterpret() const;
+    template <typename Dst> Dst        cast() const;
+
+    bool allTrue() const;
+    bool anyTrue() const;
+
+    Sk4x   bitNot()            const;
+    Sk4x   bitAnd(const Sk4x&) const;
+    Sk4x    bitOr(const Sk4x&) const;
+    Sk4x      add(const Sk4x&) const;
+    Sk4x subtract(const Sk4x&) const;
+    Sk4x multiply(const Sk4x&) const;
+    Sk4x   divide(const Sk4x&) const;
+
+    Sk4i            equal(const Sk4x&) const;
+    Sk4i         notEqual(const Sk4x&) const;
+    Sk4i         lessThan(const Sk4x&) const;
+    Sk4i      greaterThan(const Sk4x&) const;
+    Sk4i    lessThanEqual(const Sk4x&) const;
+    Sk4i greaterThanEqual(const Sk4x&) const;
+
+    static Sk4x Min(const Sk4x& a, const Sk4x& b);
+    static Sk4x Max(const Sk4x& a, const Sk4x& b);
+
+    // Swizzles follow OpenCL xyzw convention.
+    Sk4x zwxy() const;
+
+    // When there's a second argument, it's abcd.
+    static Sk4x XYAB(const Sk4x& xyzw, const Sk4x& abcd);
+    static Sk4x ZWCD(const Sk4x& xyzw, const Sk4x& abcd);
+
+private:
+    // It's handy to have Sk4f and Sk4i be mutual friends.
+    template <typename S> friend class Sk4x;
+
+#define SK4X_PRIVATE 1
+    #include "Sk4x_portable.h"
+#undef SK4X_PRIVATE
+};
+
+#include "Sk4x_portable.h"
+
+#endif//Sk4x_DEFINED