Sketch SkPMFloat

src/opts/SkPMFloat_SSE2.h

+#include "SkColorPriv.h"
+#include "SkPMFloat.h"
+#include <emmintrin.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.
+// _mm_packus_epi16() gives us clamping for free while narrowing.
+
+inline void SkPMFloat::set(SkPMColor c) {
+    SkPMColorAssert(c);
+    __m128i fix8    = _mm_set_epi32(0,0,0,c),
+            fix8_16 = _mm_unpacklo_epi8 (fix8,    _mm_setzero_si128()),
+            fix8_32 = _mm_unpacklo_epi16(fix8_16, _mm_setzero_si128());
+    __m128  scaled  = _mm_cvtepi32_ps(fix8_32);
+    _mm_store_ps(fColor, _mm_mul_ps(scaled, _mm_set1_ps(1.0f/255.0f)));
+    SkASSERT(this->isValid());
+}
+
+inline SkPMColor SkPMFloat::get() const {
+    SkASSERT(this->isValid());
+    return this->clamped();  // At the moment, we don't know anything faster.
+}
+
+inline SkPMColor SkPMFloat::clamped() const {
+    __m128  scaled  = _mm_mul_ps(_mm_load_ps(fColor), _mm_set1_ps(255.0f));
+    __m128i fix8_32 = _mm_cvtps_epi32(scaled),
+            fix8_16 = _mm_packus_epi16(fix8_32, fix8_32),
+            fix8    = _mm_packus_epi16(fix8_16, fix8_16);
+    SkPMColor c = _mm_cvtsi128_si32(fix8);
+    SkPMColorAssert(c);
+    return c;
+}