Sketch SkPMFloat

src/opts/SkPMFloat_neon.h

Index: src/opts/SkPMFloat_neon.h
diff --git a/src/opts/SkPMFloat_neon.h b/src/opts/SkPMFloat_neon.h
new file mode 100644
index 0000000000000000000000000000000000000000..f3d265573dd497a8943f215f7a813e390cdaf25f
--- /dev/null
+++ b/src/opts/SkPMFloat_neon.h
@@ -0,0 +1,42 @@
+#include "SkColorPriv.h"
+#include "SkPMFloat.h"
+#include <arm_neon.h>
+
+// For set(), we widen our 8 bit components (fix8) to 8-bit components in 16 bits (fix8_16),
+// then widen those to 8-bit-in-32-bits (fix8_32), convert those to floats (scaled),
+// then finally scale those down from [0.0f, 255.0f] to [0.0f, 1.0f] into fColor.
+
+// get() and clamped() do the opposite, working from [0.0f, 1.0f] floats to [0.0f, 255.0f],
+// to 8-bit-in-32-bit, to 8-bit-in-16-bit, back down to 8-bit components.
+// clamped() uses vqmovn to clamp while narrowing instead of just narrowing with vmovn.
+
+inline void SkPMFloat::set(SkPMColor c) {
+    SkPMColorAssert(c);
+    uint8x8_t   fix8    = (uint8x8_t)vdup_n_u32(c);
+    uint16x8_t  fix8_16 = vmovl_u8(fix8);
+    uint32x4_t  fix8_32 = vmovl_u16(vget_low_u16(fix8_16));
+    float32x4_t scaled  = vcvtq_f32_u32(fix8_32);
+    vst1q_f32(fColor, vmulq_f32(scaled, vdupq_n_f32(1.0f/255.0f)));
+    SkASSERT(this->isValid());
+}
+
+inline SkPMColor SkPMFloat::get() const {
+    SkASSERT(this->isValid());
+    float32x4_t scaled  = vmulq_f32(vld1q_f32(fColor), vdupq_n_f32(255.0f));
+    uint32x4_t  fix8_32 = vcvtq_u32_f32(scaled);
+    uint16x4_t  fix8_16 = vmovn_u32(fix8_32);
+    uint8x8_t   fix8    = vmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
+    SkPMColor c = vget_lane_u32((uint32x2_t)fix8, 0);
+    SkPMColorAssert(c);
+    return c;
+}
+
+inline SkPMColor SkPMFloat::clamped() const {
+    float32x4_t scaled  = vmulq_f32(vld1q_f32(fColor), vdupq_n_f32(255.0f));
+    uint32x4_t  fix8_32 = vcvtq_u32_f32(scaled);
+    uint16x4_t  fix8_16 = vqmovn_u32(fix8_32);
+    uint8x8_t   fix8    = vqmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
+    SkPMColor c = vget_lane_u32((uint32x2_t)fix8, 0);
+    SkPMColorAssert(c);
+    return c;
+}