Sk2x/Sk4x: add negate(), operator -()

src/core/Sk4x.h

 #ifndef Sk4x_DEFINED
 #define Sk4x_DEFINED
 
 #include "SkTypes.h"
 #include "SkNx.h"
 
 #define SK4X_PREAMBLE 1
     #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2 && !defined(SKNX_NO_SIMD)
         #include "../opts/Sk4x_sse.h"
     #elif defined(SK_ARM_HAS_NEON)                && !defined(SKNX_NO_SIMD)
@@ skipping 51 matching lines @@
     Sk4x operator *(const Sk4x& o) const { return this->multiply(o); }
     Sk4x operator /(const Sk4x& o) const { return this->divide(o); }
 
     Sk4x& operator &=(const Sk4x& o) { return (*this = *this & o); }
     Sk4x& operator |=(const Sk4x& o) { return (*this = *this | o); }
     Sk4x& operator +=(const Sk4x& o) { return (*this = *this + o); }
     Sk4x& operator -=(const Sk4x& o) { return (*this = *this - o); }
     Sk4x& operator *=(const Sk4x& o) { return (*this = *this * o); }
     Sk4x& operator /=(const Sk4x& o) { return (*this = *this / o); }
 
+    Sk4x negate() const { return Sk4x(0) - *this; }
+    Sk4x operator -() const { return this->negate(); }
+
     Sk4x rsqrt() const;   // Approximate reciprocal sqrt().
     Sk4x  sqrt() const;   // this->multiply(this->rsqrt()) may be faster, but less precise.
 
     Sk4i            equal(const Sk4x&) const;
     Sk4i         notEqual(const Sk4x&) const;
     Sk4i         lessThan(const Sk4x&) const;
     Sk4i      greaterThan(const Sk4x&) const;
     Sk4i    lessThanEqual(const Sk4x&) const;
     Sk4i greaterThanEqual(const Sk4x&) const;
 
@@ skipping 35 matching lines @@
 
 #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2 && !defined(SKNX_NO_SIMD)
     #include "../opts/Sk4x_sse.h"
 #elif defined(SK_ARM_HAS_NEON)                && !defined(SKNX_NO_SIMD)
     #include "../opts/Sk4x_neon.h"
 #else
     #include "../opts/Sk4x_none.h"
 #endif
 
 #endif//Sk4x_DEFINED