Merged 0.0 changes from revision 3234 to 3317 to trunk.

1 files changed, 24 insertions, 0 deletions

diff --git a/src/utils/fastsqrt.h b/src/utils/fastsqrt.h
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+/* A very fast function to calculate the approximate inverse square root of a

+ * floating point value and a helper function that uses it for getting the

+ * normal squareroot. For an explanation of the inverse squareroot function

+ * read:

+ * http://www.math.purdue.edu/~clomont/Math/Papers/2003/InvSqrt.pdf

+ *

+ * Unfortunately the original creator of this function seems to be unknown.

+ */

+

+float fastInvSqrt(float x)

+{

+    union { int i; float x; } tmp;

+    float xhalf = 0.5f * x;

+    tmp.x = x;

+    tmp.i = 0x5f375a86 - (tmp.i >> 1);

+    x = tmp.x;

+    x = x * (1.5f - xhalf * x * x);

+    return x;

+}

+

+float fastSqrt(float x)

+{

+    return 1.0f / fastInvSqrt(x);

+}