SkPx: new approach to fixed-point SIMD

src/core/SkPx.h

Index: src/core/SkPx.h
diff --git a/src/core/SkPx.h b/src/core/SkPx.h
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPx_DEFINED
+#define SkPx_DEFINED
+
+#include "SkTypes.h"
+#include "SkColorPriv.h"
+
+// We'll include one of src/opts/SkPx_{sse,neon,none}.h to define a type SkPx.
+//
+// SkPx represents up to SkPx::N 8888 pixels.  It's agnostic to whether these
+// are SkColors or SkPMColors; it only assumes that alpha is the high byte.
+static_assert(SK_A32_SHIFT == 24, "For both SkColor and SkPMColor, alpha is always the high byte.");
+//
+// SkPx::Alpha represents up to SkPx::N 8-bit values, usually coverage or alpha.
+// SkPx::Wide represents up to SkPx::N pixels with 16 bits per component.
+//
+// SkPx supports the following methods:
+//    static SkPx Dup(uint32_t);
+//    static SkPx Load(const uint32_t*);
+//    static SkPx Load(const uint32_t*, int n);  // where 0<n<SkPx::N
+//    void store(uint32_t*) const;
+//    void store(uint32_t*, int n) const;        // where 0<n<SkPx::N
+//
+//    Alpha alpha() const;    // argb -> a
+//    Wide widenLo() const;   // argb -> 0a0r0g0b
+//    Wide widenHi() const;   // argb -> a0r0g0b0
+//    Wide widenLoHi() const; // argb -> aarrggbb
+//
+//    SkPx    operator+(const SkPx&) const;
+//    SkPx    operator-(const SkPx&) const;
+//    SkPx saturatedAdd(const SkPx&) const;
+//
+//    Wide operator*(const Alpha&) const;  // argb * A -> (a*A)(r*A)(g*A)(b*A)
+//
+//    // Fast approximate (px*a+127)/255.
+//    // Never off by more than 1, and always correct when px or a is 0 or 255.
+//    // We use the approximation (px*a+px)/256.
+//    SkPx approxMulDiv255(const Alpha&) const;
+//
+//    SkPx addAlpha(const Alpha&) const;  // argb + A -> (a+A)rgb
+//
+// SkPx::Alpha supports the following methods:
+//    static Alpha Dup(uint8_t);
+//    static Alpha Load(const uint8_t*);
+//    static Alpha Load(const uint8_t*, int n);  // where 0<n<SkPx::N
+//
+//    Alpha inv() const;  // a -> 255-a
+//
+// SkPx::Wide supports the following methods:
+//    Wide operator+(const Wide&);
+//    Wide operator-(const Wide&);
+//    Wide shl<int bits>();
+//    Wide shr<int bits>();
+//
+//    // Return the high byte of each component of (*this + o.widenLo()).
+//    SkPx addNarrowHi(const SkPx& o);
+//
+// Methods left unwritten, but certainly to come:
+//    SkPx SkPx::operator<(const SkPx&) const;
+//    SkPx SkPx::thenElse(const SkPx& then, const SkPx& else) const;
+//    Wide Wide::operator<(const Wide&) const;
+//    Wide Wide::thenElse(const Wide& then, const Wide& else) const;
+//
+//    SkPx Wide::div255() const;  // Rounds, think (*this + 127) / 255.
+//
+//  The different implementations of SkPx have complete freedom to choose
+//  SkPx::N and how they represent SkPx, SkPx::Alpha, and SkPx::Wide.
+//
+//  All observable math must remain identical.
+
+#if defined(SKNX_NO_SIMD)
+    #include "../opts/SkPx_none.h"
+#else
+    #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
+        #include "../opts/SkPx_sse.h"
+    #elif defined(SK_ARM_HAS_NEON)
+        #include "../opts/SkPx_neon.h"
+    #else
+        #include "../opts/SkPx_none.h"
+    #endif
+#endif
+
+#endif//SkPx_DEFINED