Represent integer byte values in a human readable format.

bytes.el

;;; bytes.el --- Working with byte values -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>

;;; 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)

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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 mb.")

(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.")

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;; Functions
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(defun bytes/classify (x)
  "Return unit that closest fits byte count, X."
  (prelude/assert (number/positive? 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