tvl-depot/users/wpcarro/emacs/.emacs.d/wpc/bytes.el

;;; bytes.el --- Working with byte values -*- lexical-binding: t -*-

;; Author: William Carroll <wpcarro@gmail.com>
;; Version: 0.0.1
;; Package-Requires: ((emacs "24.3"))

;;; Commentary:
;; Functions to help with human-readable representations of byte values.
;;
;; Usage:
;; See the test cases for example usage.  Or better yet, I should use a type of
;; structured documentation that would allow me to expose a view into the test
;; suite here.  Is this currently possible in Elisp?
;;
;; API:
;; - serialize :: Integer -> String
;;
;; Wish list:
;; - Rounding: e.g. (bytes (* 1024 1.7)) => "2KB"

;;; Code:

;; TODO: Support -ibabyte variants like Gibibyte (GiB).

;; Ranges:
;;  B: [   0,  1e3)
;; KB: [ 1e3,  1e6)
;; MB: [ 1e6,  1e6)
;; GB: [ 1e9, 1e12)
;; TB: [1e12, 1e15)
;; PB: [1e15, 1e18)
;;
;; Note: I'm currently not support exabytes because that causes the integer to
;;  overflow.  I imagine a larger integer type may exist, but for now, I'll
;;  treat this as a YAGNI.

(require 'prelude)
(require 'tuple)
(require 'math)
(require 'number)

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;; Constants
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(defconst bytes-kb (math-exp 2 10)
  "Number of bytes in a kilobyte.")

(defconst bytes-mb (math-exp 2 20)
  "Number of bytes in a megabytes.")

(defconst bytes-gb (math-exp 2 30)
  "Number of bytes in a gigabyte.")

(defconst bytes-tb (math-exp 2 40)
  "Number of bytes in a terabyte.")

(defconst bytes-pb (math-exp 2 50)
  "Number of bytes in a petabyte.")

(defconst bytes-eb (math-exp 2 60)
  "Number of bytes in an exabyte.")

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;; Functions
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(defun bytes-classify (x)
  "Return unit that closest fits byte count, X."
  (prelude-assert (number-whole? x))
  (cond
   ((and (>= x 0)        (< x bytes-kb))     'byte)
   ((and (>= x bytes-kb) (< x bytes-mb)) 'kilobyte)
   ((and (>= x bytes-mb) (< x bytes-gb)) 'megabyte)
   ((and (>= x bytes-gb) (< x bytes-tb)) 'gigabyte)
   ((and (>= x bytes-tb) (< x bytes-pb)) 'terabyte)
   ((and (>= x bytes-pb) (< x bytes-eb)) 'petabyte)))

(defun bytes-to-string (x)
  "Convert integer X into a human-readable string."
  (let ((base-and-unit
         (pcase (bytes-classify x)
           ('byte     (tuple/from        1 "B"))
           ('kilobyte (tuple/from bytes-kb "KB"))
           ('megabyte (tuple/from bytes-mb "MB"))
           ('gigabyte (tuple/from bytes-gb "GB"))
           ('terabyte (tuple/from bytes-tb "TB"))
           ('petabyte (tuple/from bytes-pb "PB")))))
    (string-format "%d%s"
                   (round x (tuple/first base-and-unit))
                   (tuple/second base-and-unit))))

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;; Tests
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(progn
  (prelude-assert
   (equal "1000B" (bytes-to-string 1000)))
  (prelude-assert
   (equal "2KB" (bytes-to-string (* 2 bytes-kb))))
  (prelude-assert
   (equal "17MB" (bytes-to-string (* 17 bytes-mb))))
  (prelude-assert
   (equal "419GB" (bytes-to-string (* 419 bytes-gb))))
  (prelude-assert
   (equal "999TB" (bytes-to-string (* 999 bytes-tb))))
  (prelude-assert
   (equal "2PB" (bytes-to-string (* 2 bytes-pb)))))

(provide 'bytes)
;;; bytes.el ends here