SKPMFloat: we can beat the naive loops when clamping

src/opts/SkPMFloat_SSE2.h

 #include "SkColorPriv.h"
 #include <emmintrin.h>
 
 // For SkPMFloat(SkPMColor), 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), and finally convert those to floats.
 
 // get() and clamped() do the opposite, working from floats 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 SkPMFloat::SkPMFloat(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());
     _mm_store_ps(fColor, _mm_cvtepi32_ps(fix8_32));
     SkASSERT(this->isValid());
 }
 
 inline SkPMColor SkPMFloat::get() const {
     SkASSERT(this->isValid());
-    return this->clamped();  // At the moment, we don't know anything faster.
+    return this->clamped();  // Haven't beaten this yet.
 }
 
 inline SkPMColor SkPMFloat::clamped() const {
     __m128i fix8_32 = _mm_cvtps_epi32(_mm_load_ps(fColor)),  // _mm_cvtps_epi32 rounds for us!
             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;
 }
+
+inline void SkPMFloat::From4PMColors(SkPMFloat floats[4], const SkPMColor colors[4]) {
+    // Haven't beaten this yet.
+    for (int i = 0; i < 4; i++) { floats[i] = FromPMColor(colors[i]); }
+}
+
+inline void SkPMFloat::To4PMColors(SkPMColor colors[4], const SkPMFloat floats[4]) {
+    SkASSERT(floats[0].isValid() && floats[1].isValid()
+          && floats[2].isValid() && floats[3].isValid());
+    // Haven't beaten this yet.
+    ClampTo4PMColors(colors, floats);
+}
+
+inline void SkPMFloat::ClampTo4PMColors(SkPMColor colors[4], const SkPMFloat floats[4]) {
+    // Same as _SSSE3.h's.  We use 3 _mm_packus_epi16() where the naive loop uses 8.
+    __m128i c0 = _mm_cvtps_epi32(_mm_load_ps(floats[0].fColor)),  // _mm_cvtps_epi32 rounds for us!
+            c1 = _mm_cvtps_epi32(_mm_load_ps(floats[1].fColor)),
+            c2 = _mm_cvtps_epi32(_mm_load_ps(floats[2].fColor)),
+            c3 = _mm_cvtps_epi32(_mm_load_ps(floats[3].fColor));
+    __m128i c3210 = _mm_packus_epi16(_mm_packus_epi16(c0, c1),
+                                     _mm_packus_epi16(c2, c3));
+    _mm_storeu_si128((__m128i*)colors, c3210);
+    SkPMColorAssert(colors[0]);
+    SkPMColorAssert(colors[1]);
+    SkPMColorAssert(colors[2]);
+    SkPMColorAssert(colors[3]);
+}