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(in-package :xlisp)
(export 'rationalize)
(defun rationalize (val) ; hopefully readable conversion
(unless (typep val 'flonum)
(if (typep val 'rational)
(return-from rationalize val)
(error "~s is invalid type" val)))
(let ((fraction (abs (rem val 1.0))))
(if (zerop fraction)
(round val)
(let ((limit (expt 10 (- (+ 7 (truncate (log fraction 10)))
(max 0 (truncate (log (abs val) 10))))))
divisor)
(cond ((>= limit 10000) ; allow primes 3 3 7 11 13
(setq limit (* 9009 (/ limit 10000))))
((>= limit 1000) ; allow primes 3 3 7 11
(setq limit (* 693 (/ limit 1000))))
((>= limit 100) ; allow primes 3 3 7
(setq limit (* 63 (/ limit 100)))))
(setq divisor (round (/ limit fraction)))
(if (floatp divisor)
(round val) ; Doesn't fit
(/ (round (* val divisor)) divisor))))))
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