SkPx: new approach to fixed-point SIMD

src/opts/SkPx_neon.h

Index: src/opts/SkPx_neon.h
diff --git a/src/opts/SkPx_neon.h b/src/opts/SkPx_neon.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_neon_DEFINED
+#define SkPx_neon_DEFINED
+
+// When we have NEON, we like to work 8 pixels at a time.
+// This lets us exploit vld4/vst4 and represent SkPx as planar uint8x8x4_t,
+// Wide as planar uint16x8x4_t, and Alpha as a single uint8x8_t plane.
+
+struct SkPx_neon {
+    static const int N = 8;
+
+    uint8x8x4_t fVec;
+    SkPx_neon(uint8x8x4_t vec) : fVec(vec) {}
+
+    static SkPx_neon Dup(uint32_t px) { return vld4_dup_u8((const uint8_t*)&px); }
+    static SkPx_neon Load(const uint32_t* px) { return vld4_u8((const uint8_t*)px); }
+    static SkPx_neon Load(const uint32_t* px, int n) {
+        SkASSERT(0 < n && n < 8);
+        uint8x8x4_t v = vld4_dup_u8((const uint8_t*)px);  // n>=1, so start all lanes with pixel 0.
+        switch (n) {
+            case 7: v = vld4_lane_u8((const uint8_t*)(px+6), v, 6);  // fall through
+            case 6: v = vld4_lane_u8((const uint8_t*)(px+5), v, 5);  // fall through
+            case 5: v = vld4_lane_u8((const uint8_t*)(px+4), v, 4);  // fall through
+            case 4: v = vld4_lane_u8((const uint8_t*)(px+3), v, 3);  // fall through
+            case 3: v = vld4_lane_u8((const uint8_t*)(px+2), v, 2);  // fall through
+            case 2: v = vld4_lane_u8((const uint8_t*)(px+1), v, 1);
+        }
+        return v;
+    }
+
+    void store(uint32_t* px) const { vst4_u8((uint8_t*)px, fVec); }
+    void store(uint32_t* px, int n) const {
+        SkASSERT(0 < n && n < 8);
+        switch (n) {
+            case 7: vst4_lane_u8((uint8_t*)(px+6), fVec, 6);
+            case 6: vst4_lane_u8((uint8_t*)(px+5), fVec, 5);
+            case 5: vst4_lane_u8((uint8_t*)(px+4), fVec, 4);
+            case 4: vst4_lane_u8((uint8_t*)(px+3), fVec, 3);
+            case 3: vst4_lane_u8((uint8_t*)(px+2), fVec, 2);
+            case 2: vst4_lane_u8((uint8_t*)(px+1), fVec, 1);
+            case 1: vst4_lane_u8((uint8_t*)(px+0), fVec, 0);
+        }
+    }
+
+    struct Alpha {
+        uint8x8_t fA;
+        Alpha(uint8x8_t a) : fA(a) {}
+
+        static Alpha Dup(uint8_t a) { return vdup_n_u8(a); }
+        static Alpha Load(const uint8_t* a) { return vld1_u8(a); }
+        static Alpha Load(const uint8_t* a, int n) {
+            SkASSERT(0 < n && n < 8);
+            uint8x8_t v = vld1_dup_u8(a);  // n>=1, so start all lanes with alpha 0.
+            switch (n) {
+                case 7: v = vld1_lane_u8(a+6, v, 6);  // fall through
+                case 6: v = vld1_lane_u8(a+5, v, 5);  // fall through
+                case 5: v = vld1_lane_u8(a+4, v, 4);  // fall through
+                case 4: v = vld1_lane_u8(a+3, v, 3);  // fall through
+                case 3: v = vld1_lane_u8(a+2, v, 2);  // fall through
+                case 2: v = vld1_lane_u8(a+1, v, 1);
+            }
+            return v;
+        }
+        Alpha inv() const { return vsub_u8(vdup_n_u8(255), fA); }
+    };
+
+    struct Wide {
+        uint16x8x4_t fVec;
+        Wide(uint16x8x4_t vec) : fVec(vec) {}
+
+        Wide operator+(const Wide& o) const {
+            return (uint16x8x4_t) {{
+                vaddq_u16(fVec.val[0], o.fVec.val[0]),
+                vaddq_u16(fVec.val[1], o.fVec.val[1]),
+                vaddq_u16(fVec.val[2], o.fVec.val[2]),
+                vaddq_u16(fVec.val[3], o.fVec.val[3]),
+            }};
+        }
+        Wide operator-(const Wide& o) const {
+            return (uint16x8x4_t) {{
+                vsubq_u16(fVec.val[0], o.fVec.val[0]),
+                vsubq_u16(fVec.val[1], o.fVec.val[1]),
+                vsubq_u16(fVec.val[2], o.fVec.val[2]),
+                vsubq_u16(fVec.val[3], o.fVec.val[3]),
+            }};
+        }
+
+        template <int bits> Wide shl() const {
+            return (uint16x8x4_t) {{
+                vshlq_n_u16(fVec.val[0], bits),
+                vshlq_n_u16(fVec.val[1], bits),
+                vshlq_n_u16(fVec.val[2], bits),
+                vshlq_n_u16(fVec.val[3], bits),
+            }};
+        }
+        template <int bits> Wide shr() const {
+            return (uint16x8x4_t) {{
+                vshrq_n_u16(fVec.val[0], bits),
+                vshrq_n_u16(fVec.val[1], bits),
+                vshrq_n_u16(fVec.val[2], bits),
+                vshrq_n_u16(fVec.val[3], bits),
+            }};
+        }
+
+        SkPx_neon addNarrowHi(const SkPx_neon& o) const {
+            return (uint8x8x4_t) {{
+                vshrn_n_u16(vaddw_u8(fVec.val[0], o.fVec.val[0]), 8),
+                vshrn_n_u16(vaddw_u8(fVec.val[1], o.fVec.val[1]), 8),
+                vshrn_n_u16(vaddw_u8(fVec.val[2], o.fVec.val[2]), 8),
+                vshrn_n_u16(vaddw_u8(fVec.val[3], o.fVec.val[3]), 8),
+            }};
+        }
+    };
+
+    Alpha alpha() const { return fVec.val[3]; }
+
+    Wide widenLo() const {
+        return (uint16x8x4_t) {{
+            vmovl_u8(fVec.val[0]),
+            vmovl_u8(fVec.val[1]),
+            vmovl_u8(fVec.val[2]),
+            vmovl_u8(fVec.val[3]),
+        }};
+    }
+    // TODO: these two can probably be done faster.
+    Wide widenHi() const { return this->widenLo().shl<8>(); }
+    Wide widenLoHi() const { return this->widenLo() + this->widenHi(); }
+
+    SkPx_neon operator+(const SkPx_neon& o) const {
+        return (uint8x8x4_t) {{
+            vadd_u8(fVec.val[0], o.fVec.val[0]),
+            vadd_u8(fVec.val[1], o.fVec.val[1]),
+            vadd_u8(fVec.val[2], o.fVec.val[2]),
+            vadd_u8(fVec.val[3], o.fVec.val[3]),
+        }};
+    }
+    SkPx_neon operator-(const SkPx_neon& o) const {
+        return (uint8x8x4_t) {{
+            vsub_u8(fVec.val[0], o.fVec.val[0]),
+            vsub_u8(fVec.val[1], o.fVec.val[1]),
+            vsub_u8(fVec.val[2], o.fVec.val[2]),
+            vsub_u8(fVec.val[3], o.fVec.val[3]),
+        }};
+    }
+    SkPx_neon saturatedAdd(const SkPx_neon& o) const {
+        return (uint8x8x4_t) {{
+            vqadd_u8(fVec.val[0], o.fVec.val[0]),
+            vqadd_u8(fVec.val[1], o.fVec.val[1]),
+            vqadd_u8(fVec.val[2], o.fVec.val[2]),
+            vqadd_u8(fVec.val[3], o.fVec.val[3]),
+        }};
+    }
+
+    Wide operator*(const Alpha& a) const {
+        return (uint16x8x4_t) {{
+            vmull_u8(fVec.val[0], a.fA),
+            vmull_u8(fVec.val[1], a.fA),
+            vmull_u8(fVec.val[2], a.fA),
+            vmull_u8(fVec.val[3], a.fA),
+        }};
+    }
+    SkPx_neon approxMulDiv255(const Alpha& a) const {
+        return (*this * a).addNarrowHi(*this);
+    }
+
+    SkPx_neon addAlpha(const Alpha& a) const {
+        return (uint8x8x4_t) {{
+            fVec.val[0],
+            fVec.val[1],
+            fVec.val[2],
+            vadd_u8(fVec.val[3], a.fA),
+        }};
+    }
+};
+typedef SkPx_neon SkPx;
+
+#endif//SkPx_neon_DEFINED