Add sqrt() and rsqrt() to Sk4f.

tests/Sk4xTest.cpp

 #include "Test.h"
 #include "Sk4x.h"
 
 #define ASSERT_EQ(a, b) REPORTER_ASSERT(r, a.equal(b).allTrue())
 #define ASSERT_NE(a, b) REPORTER_ASSERT(r, a.notEqual(b).allTrue())
 
 DEF_TEST(Sk4x_Construction, r) {
     Sk4f uninitialized;
     Sk4f zero(0,0,0,0);
     Sk4f foo(1,2,3,4),
@@ skipping 69 matching lines @@
 
     ASSERT_EQ(Sk4i(4,6,8,10),    Sk4i(1,2,3,4).add(Sk4i(3,4,5,6)));
     ASSERT_EQ(Sk4i(-2,-2,-2,-2), Sk4i(1,2,3,4).subtract(Sk4i(3,4,5,6)));
     ASSERT_EQ(Sk4i(3,8,15,24),   Sk4i(1,2,3,4).multiply(Sk4i(3,4,5,6)));
 }
 
 DEF_TEST(Sk4x_ImplicitPromotion, r) {
     ASSERT_EQ(Sk4f(2,4,6,8), Sk4f(1,2,3,4).multiply(2.0f));
 }
 
+DEF_TEST(Sk4x_Sqrt, r) {
+    Sk4f squares(4, 16, 25, 121),
+           roots(2,  4,  5,  11);
+    // .sqrt() should be pretty precise.
+    ASSERT_EQ(roots, squares.sqrt());
+
+    // .rsqrt() isn't so precise, but should be pretty close.
+    Sk4f error = roots.subtract(squares.multiply(squares.rsqrt()));
+    REPORTER_ASSERT(r, error.greaterThan(0.0f).allTrue());
+    REPORTER_ASSERT(r, error.lessThan(0.01f).allTrue());
+}
+
 DEF_TEST(Sk4x_Comparison, r) {
     ASSERT_EQ(Sk4f(1,2,3,4), Sk4f(1,2,3,4));
     ASSERT_NE(Sk4f(4,3,2,1), Sk4f(1,2,3,4));
 
     ASSERT_EQ(Sk4i(-1,-1,0,-1), Sk4f(1,2,5,4).equal(Sk4f(1,2,3,4)));
 
     ASSERT_EQ(Sk4i(-1,-1,-1,-1), Sk4f(1,2,3,4).lessThan(Sk4f(2,3,4,5)));
     ASSERT_EQ(Sk4i(-1,-1,-1,-1), Sk4f(1,2,3,4).lessThanEqual(Sk4f(2,3,4,5)));
     ASSERT_EQ(Sk4i(0,0,0,0),     Sk4f(1,2,3,4).greaterThan(Sk4f(2,3,4,5)));
     ASSERT_EQ(Sk4i(0,0,0,0),     Sk4f(1,2,3,4).greaterThanEqual(Sk4f(2,3,4,5)));
@@ skipping 17 matching lines @@
 }
 
 DEF_TEST(Sk4x_Swizzle, r) {
     ASSERT_EQ(Sk4f(3,4,1,2), Sk4f(1,2,3,4).zwxy());
     ASSERT_EQ(Sk4f(1,2,5,6), Sk4f::XYAB(Sk4f(1,2,3,4), Sk4f(5,6,7,8)));
     ASSERT_EQ(Sk4f(3,4,7,8), Sk4f::ZWCD(Sk4f(1,2,3,4), Sk4f(5,6,7,8)));
     ASSERT_EQ(Sk4i(3,4,1,2), Sk4i(1,2,3,4).zwxy());
     ASSERT_EQ(Sk4i(1,2,5,6), Sk4i::XYAB(Sk4i(1,2,3,4), Sk4i(5,6,7,8)));
     ASSERT_EQ(Sk4i(3,4,7,8), Sk4i::ZWCD(Sk4i(1,2,3,4), Sk4i(5,6,7,8)));
 }