gistfile1.cl

;; xyzzy の epsilon 周りがおかしい
;;
;; http://twitter.com/TwilightClover/status/26251344464
;; http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/convar_short-_tive-epsilon.html

(defconstant my-short-float-epsilon
  (do* ((fe 1.1s0 fl)
        (fl 1.0s0 (/ fl 2.0s0)))
      ((not (and (/= (+ 1.0s0 fl) 1.0s0)
                 (> fe fl)))
       fe)))
(defconstant my-short-float-negative-epsilon
  (do* ((fe 1.1s0 fl)
        (fl 1.0s0 (/ fl 2.0s0)))
      ((not (and (/= (- 1.0s0 fl) 1.0s0)
                 (> fe fl)))
       fe)))

(dolist (sym '((double-float-epsilon t)
               (double-float-negative-epsilon nil)
               (long-float-epsilon t)
               (long-float-negative-epsilon nil)
               (short-float-epsilon t)
               (short-float-negative-epsilon nil)
               (single-float-epsilon t)
               (single-float-negative-epsilon nil)
               (my-short-float-epsilon t)
               (my-short-float-negative-epsilon nil)))
  (let ((epsilon (symbol-value (car sym)))
        (positive (cadr sym)))
    (format t "~32S = ~32S test = ~S~%"
            (car sym)
            epsilon
            (if positive
                (not (= (float 1 epsilon) (+ (float 1 epsilon) epsilon)))
              (not (= (float 1 epsilon) (- (float 1 epsilon) epsilon)))))
    ))

gistfile2.txt

;; xyzzy 0.2.2.235
double-float-epsilon             = 2.220446049250313d-16            test = t
double-float-negative-epsilon    = 1.110223024625157d-16            test = t
long-float-epsilon               = 2.220446049250313d-16            test = t
long-float-negative-epsilon      = 1.110223024625157d-16            test = t
short-float-epsilon              = 2.220446e-16                     test = nil
short-float-negative-epsilon     = 1.110223e-16                     test = nil
single-float-epsilon             = 2.220446e-16                     test = nil
single-float-negative-epsilon    = 1.110223e-16                     test = nil
my-short-float-epsilon           = 1.192093e-7                      test = t
my-short-float-negative-epsilon  = 5.960464e-8                      test = t
nil