Sk4f: add floor()

src/opts/SkNx_sse.h

 /*
  * 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 SkNx_sse_DEFINED
 #define SkNx_sse_DEFINED
 
 // This file may assume <= SSE2, but must check SK_CPU_SSE_LEVEL for anything more recent.
 // If you do, make sure this is in a static inline function... anywhere else risks violating ODR.
 
 #define SKNX_IS_FAST
 
+// SSE 4.1 has _mm_floor_ps to floor 4 floats.  We emulate it:
+//   - round by adding (1<<23) with our sign, then subtracting it;
+//   - if that rounded value is bigger than our input, subtract 1.
+static inline __m128 sse2_mm_floor_ps(__m128 v) {
+    __m128 sign = _mm_and_ps(v, _mm_set1_ps(-0.0f));
+    __m128 bias = _mm_or_ps(sign, _mm_set1_ps(1<<23));
+    __m128 rounded = _mm_sub_ps(_mm_add_ps(v, bias), bias);
+    __m128 too_big = _mm_cmpgt_ps(rounded, v);
+    return _mm_sub_ps(rounded, _mm_and_ps(too_big, _mm_set1_ps(1.0f)));
+}
+
 template <>
 class SkNx<2, float> {
 public:
     SkNx(const __m128& vec) : fVec(vec) {}
 
     SkNx() {}
     SkNx(float val) : fVec(_mm_set1_ps(val)) {}
     static SkNx Load(const void* ptr) {
         return _mm_castsi128_ps(_mm_loadl_epi64((const __m128i*)ptr));
     }
@@ skipping 59 matching lines @@
     SkNx operator != (const SkNx& o) const { return _mm_cmpneq_ps(fVec, o.fVec); }
     SkNx operator  < (const SkNx& o) const { return _mm_cmplt_ps (fVec, o.fVec); }
     SkNx operator  > (const SkNx& o) const { return _mm_cmpgt_ps (fVec, o.fVec); }
     SkNx operator <= (const SkNx& o) const { return _mm_cmple_ps (fVec, o.fVec); }
     SkNx operator >= (const SkNx& o) const { return _mm_cmpge_ps (fVec, o.fVec); }
 
     static SkNx Min(const SkNx& l, const SkNx& r) { return _mm_min_ps(l.fVec, r.fVec); }
     static SkNx Max(const SkNx& l, const SkNx& r) { return _mm_max_ps(l.fVec, r.fVec); }
 
     SkNx abs() const { return _mm_andnot_ps(_mm_set1_ps(-0.0f), fVec); }
+    SkNx floor() const { return sse2_mm_floor_ps(fVec); }
 
     SkNx  sqrt () const { return _mm_sqrt_ps (fVec);  }
     SkNx rsqrt0() const { return _mm_rsqrt_ps(fVec); }
     SkNx rsqrt1() const { return this->rsqrt0(); }
     SkNx rsqrt2() const { return this->rsqrt1(); }
 
     SkNx       invert() const { return SkNx(1) / *this; }
     SkNx approxInvert() const { return _mm_rcp_ps(fVec); }
 
     float operator[](int k) const {
@@ skipping 231 matching lines @@
 
 template<> /*static*/ inline Sk4h SkNx_cast<uint16_t, uint8_t>(const Sk4b& src) {
     return _mm_unpacklo_epi8(src.fVec, _mm_setzero_si128());
 }
 
 template<> /*static*/ inline Sk4b SkNx_cast<uint8_t, uint16_t>(const Sk4h& src) {
     return _mm_packus_epi16(src.fVec, src.fVec);
 }
 
 #endif//SkNx_sse_DEFINED