(in-package :cl-user)

(defun single-float-uint32 (x)
  (rlet ((a :single-float x))
    (%get-unsigned-long a 0)))

(defun uint32-single-float (x)
  (rlet ((a (:unsigned 32) x))
    (%get-single-float a 0)))

(defun rsqrt (number)
  (let ((x/2 (* number 0.5f0))
        (y (uint32-single-float (- #x5f3759df (ash (single-float-uint32 number) -1)))))
    (setf y (* y (- 1.5f0 (* x/2 y y))))
    ;; (setf y (* y (- 1.5f0 (* x/2 y y))))
    y))