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- Log ----------------------------------------------------------------- commit b1d9be467f5f44383a356a4a11a04a64f0f29402 Author: Raymond Toy toy.raymond@gmail.com Date: Wed Nov 27 09:09:50 2013 -0800

Add implementation for tan(x) using duplication.

Includes Lentz' algorithm for evaluating continued fractions and updates the timing test to include tan(x) using duplication. Tests show this is much slower than existing algorithms.

diff --git a/qd-extra.lisp b/qd-extra.lisp index 61ce7e4..3670be5 100644 --- a/qd-extra.lisp +++ b/qd-extra.lisp @@ -993,6 +993,66 @@ y (add-qd (mul-qd y ct) (mul-qd x st))) (div-qd y x))))

+(defvar *debug-cf-eval* nil) +(defvar *max-cf-iterations* 10000) + +(defun lentz-qd (bf af) + (let ((tiny-value-count 0)) + (flet ((value-or-tiny (v) + (cond ((zerop-qd v) + (incf tiny-value-count) + (make-qd-d (sqrt least-positive-normalized-double-float))) + (t + v)))) + (let* ((f (value-or-tiny (funcall bf 0))) + (c f) + (d (make-qd-d 0d0)) + (eps +qd-eps+)) + (loop + for j from 1 upto *max-cf-iterations* + for an = (funcall af j) + for bn = (funcall bf j) + do (progn + (setf d (value-or-tiny (add-qd bn (mul-qd an d)))) + (setf c (value-or-tiny (add-qd bn (div-qd an c)))) + (when *debug-cf-eval* + (format t "~&j = ~d~%" j) + (format t " an = ~s~%" an) + (format t " bn = ~s~%" bn) + (format t " c = ~s~%" c) + (format t " d = ~s~%" d)) + (let ((delta (div-qd c d))) + (setf d (div-qd +qd-one+ d)) + (setf f (mul-qd f delta)) + (when *debug-cf-eval* + (format t " dl= ~S (|dl - 1| = ~S)~%" delta (abs (1- delta))) + (format t " f = ~S~%" f)) + (when (qd-<= (abs-qd (sub-qd-d delta 1d0)) eps) + (return-from lentz-qd (values f j tiny-value-count))))) + finally + (error 'simple-error + :format-control "~<Continued fraction failed to converge after ~D iterations.~% Delta = ~S~>" + :format-arguments (list *max-cf-iterations* (/ c d)))))))) + +(defun tan-qd/duplication (x) + ;; tan(x) = 2*tan(x/2)/(1-tan(x/2)^2) + (cond ((< (abs (qd-0 x)) 1d-4) + ;; Continued fraction for tan(x) + ;; + ;; x + ;; tan(x) = ----------------------------- + ;; 1 - K(2*k+1, -z^2, k, 0, inf) + (let ((x2 (neg-qd (sqr-qd x)))) + (div-qd x + (lentz-qd #'(lambda (n) + (octi::make-qd-d (float (+ (* 2 n) 1) 1d0))) + #'(lambda (n) + (declare (ignore n)) + x2))))) + (t + (let* ((tanx/2 (tan-qd/duplication (scale-float-qd x -1)))) + (/ (mul-qd-d tanx/2 2d0) + (sub-d-qd 1d0 (sqr-qd tanx/2)))))))

(defun sin-qd/cordic (r) (declare (type %quad-double r)) @@ -1374,17 +1434,22 @@ (format t "atan2-qd/newton~%") (time (dotimes (k n) (declare (fixnum k)) - (setf y (atan2-qd/newton x one)))) + (setf y (octi::atan2-qd/newton x one)))) #+cmu (ext:gc :full t) (format t "atan2-qd/cordic~%") (time (dotimes (k n) (declare (fixnum k)) - (setf y (atan2-qd/cordic x one)))) + (setf y (octi::atan2-qd/cordic x one)))) #+cmu (ext:gc :full t) (format t "atan-qd/duplication~%") (time (dotimes (k n) (declare (fixnum k)) - (setf y (atan-qd/duplication x)))) + (setf y (octi::atan-qd/duplication x)))) + #+cmu (ext:gc :full t) + (format t "atan-qd/taylor~%") + (time (dotimes (k n) + (declare (fixnum k)) + (setf y (octi::atan-qd/taylor x)))) )) ;; (time-tan #c(10w0 0) 10000)

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Summary of changes: qd-extra.lisp | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 68 insertions(+), 3 deletions(-)

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