Add sk_float_rsqrt with SSE + NEON fast paths.

src/core/SkPoint.cpp

 
 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkPoint.h"
@@ skipping 145 matching lines @@
  *  doubles, which is much slower (3x in a desktop test) but will not overflow.
  */
 bool SkPoint::setLength(float x, float y, float length) {
     float mag2;
     if (isLengthNearlyZero(x, y, &mag2)) {
         return false;
     }
 
     float scale;
     if (SkScalarIsFinite(mag2)) {
-        scale = length / sk_float_sqrt(mag2);
+        scale = length * sk_float_rsqrt(mag2);

[reed1, 2013/11/07 22:28:44]

not prepared to land this, until we know more about the assumption of *all* of
our callers.

consider adding setFastLength() for now?

     } else {
         // our mag2 step overflowed to infinity, so use doubles instead.
         // much slower, but needed when x or y are very large, other wise we
         // divide by inf. and return (0,0) vector.
         double xx = x;
         double yy = y;
         scale = (float)(length / sqrt(xx * xx + yy * yy));
     }
     fX = x * scale;
     fY = y * scale;
@@ skipping 331 matching lines @@
 
     if (uDotV <= 0) {
         return v.lengthSqd();
     } else if (uDotV > uLengthSqd) {
         return b.distanceToSqd(*this);
     } else {
         SkScalar det = u.cross(v);
         return SkScalarMulDiv(det, det, uLengthSqd);
     }
 }