common lisp - how to implement CCL::DOUBLE-FLOAT-FROM-BITS function -


i want use cl-olefs package.but found cantains plantform dependent function double-float-from-bits.

so want write function double-float-from-bits can run on plantform independently. have no idea how implment it.

or there independent functions double-float-from-bits can replaced into
cl-olefs package.

something along these lines. not terribly efficient, should quite portable.

(defun double-float-from-bits (high low)   (let* ((negative (not (zerop (logand high #x80000000))))          (mant (+ low (* #x100000000 (logand high #xfffff))))          (exbits (logand (ash high -20) #x7ff))          (ex (coerce (expt 2 (- exbits 1075)) 'double-float))          (base (coerce (+ #x10000000000000 mant) 'double-float)))     (cond ((and (zerop exbits)                 (zerop mant))            (if negative -0.0 0.0))           ((zerop exbits)            'subnormal)           ((and (= #x7ff exbits)                 (zerop mant))            (if negative 'negative-infinity 'positive-infinity))           ((= #x7ff exbits)            'not-a-number)           (negative            (- (* base ex)))           (t            (* base ex)))))

note common lisp spec not require internal floating point representation of ieee 754; requirements bit less strict. additionally, there no means of portably expressing infinities or not-a-numbers, , chose not support subnormals.

also, there may small rounding errors, depending on implementation.


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