Revert of de-proc sk_float_rsqrt

src/opts/SkFloatingPoint_opts.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 SkFloatingPoint_opts_DEFINED
+#define SkFloatingPoint_opts_DEFINED
+
+#include "SkFloatingPoint.h"
+
+namespace SK_OPTS_NS {
+
+#if defined(SK_ARM_HAS_NEON)
+    static float rsqrt(float x) {
+        return sk_float_rsqrt(x);  // This sk_float_rsqrt copy will take the NEON compile-time path.
+    }
+#else
+    static float rsqrt(float x) {
+        // Get initial estimate.
+        int i = *SkTCast<int*>(&x);
+        i = 0x5F1FFFF9 - (i>>1);
+        float estimate = *SkTCast<float*>(&i);
+
+        // One step of Newton's method to refine.
+        const float estimate_sq = estimate*estimate;
+        estimate *= 0.703952253f*(2.38924456f-x*estimate_sq);
+        return estimate;
+    }
+#endif
+
+}  // namespace SK_OPTS_NS
+
+#endif//SkFloatingPoint_opts_DEFINED