Add sqrt() and rsqrt() to Sk4f.

src/core/Sk4x_portable.h

Index: src/core/Sk4x_portable.h
diff --git a/src/core/Sk4x_portable.h b/src/core/Sk4x_portable.h
index bd056c777eef682dc8b01df1fec6c9f16fcf7976..440e91faaa581b87a0d5441256bc62c0fe88538f 100644
--- a/src/core/Sk4x_portable.h
+++ b/src/core/Sk4x_portable.h
@@ -2,6 +2,8 @@
 // This file will be intentionally included three times.
 
 #if defined(SK4X_PREAMBLE)
+    #include "SkFloatingPoint.h"
+    #include <math.h>
 
 #elif defined(SK4X_PRIVATE)
     typedef T Type;
@@ -60,6 +62,20 @@ M(Sk4x<T>) multiply(const Sk4x<T>& other) const { return Sk4x(BINOP(*)); }
 M(Sk4x<T>)   divide(const Sk4x<T>& other) const { return Sk4x(BINOP(/)); }
 #undef BINOP
 
+template<> inline Sk4f Sk4f::rsqrt() const {
+    return Sk4f(sk_float_rsqrt(fVec[0]),
+                sk_float_rsqrt(fVec[1]),
+                sk_float_rsqrt(fVec[2]),
+                sk_float_rsqrt(fVec[3]));
+}
+
+template<> inline Sk4f Sk4f::sqrt() const {
+    return Sk4f(sqrtf(fVec[0]),
+                sqrtf(fVec[1]),
+                sqrtf(fVec[2]),
+                sqrtf(fVec[3]));
+}
+
 #define BOOL_BINOP(op) fVec[0] op other.fVec[0] ? -1 : 0, \
                        fVec[1] op other.fVec[1] ? -1 : 0, \
                        fVec[2] op other.fVec[2] ? -1 : 0, \