bike shifting - output decimal in percent

[Emanuel Berg]

How do I output a decimal float digit
0 <= x <= 1 into percent? ("A percentage?"
Correct English?)

I asked at #emacs@irc.freenode.net and got the
below answer, which, as you see, works fine.

But I wonder if/why-not there is/isn't
a built-in way to do it?


Context:

;; thanks to friend at #emacs
(defun percent-string (decimal)
  (concat
   (number-to-string
    (round (* 100 decimal)) ) "%") )
;; test: (percent-string 0.42857142857142855) ; "43%"

(defun bike-compute-step (from to)
  (percent-string
   (/ (- from to)
      from
      1.0) ))
;; test - should be 43% for
;; one 42t and one 24t chainring
;; according to an article in the spring 2019 issue
;; of "Bicycle Quarterly" (ISSN 1941-8809) -
;; (bike-compute-step 42 24) ; "43%"


Whole file:

  http://user.it.uu.se/~embe8573/emacs-init/bike.el

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