Re: Strange results

["Pascal J. Bourguignon" <pjb@informatimago.com>]

Dwaddle <rmborchers@gmail.com> writes:

> Hi
>
> i've been dabbling around in elisp for a while. Made this function
>
> The issue is the byte var which 'remembers' the result from a previous calculation.
>
> (integer-bin 5)     [0 0 0 0 0 1 0 1]
> (integer-bin 3)     [0 0 0 0 0 1 1 1]
>
> To beat the critics I know it isn't very clean programmed and a loop would make it al lot shorter

Yes, use a loop!


> <code>
> (defun integer-bin (dec)
>   "Convert integer to binairy"
>   (setq 8bit [128 64 32 16 8 4 2 1])
>   (setq byte [0 0 0 0 0 0 0 0])


Instead of setq, use let to introduce local variables.


[0 0 0 0 0 0 0 0] is a literal "constant" vector.

(vector 0 0 0 0 0 0 0 0) produces a new mutable vector.

(make-vector 8 0) produces a new mutable vector with each slot
                  initialized to the same object..



(require 'cl)
         
(defun* integer-bin (integer &optional (word-size 8))
   "Convert `integer' to binary"
   (let ((word (make-vector word-size 0))) ; a new mutable vector
      (loop
        for bit-index from (1- word-size) downto 0
        for current = integer then (truncate current 2) ; or (ash current -1)
        for bit = (mod current 2)                       ; or (logand current 1)
         do (setf (aref word  bit-index) bit))
      word))

(integer-bin 42)     ; --> [0 0 1 0 1 0 1 0]
(integer-bin 42 16)  ; --> [0 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0]


(defun integer-to-base (integer base word-size)
   "Convert `integer' to base `base', over `word-size` digits."
   (let ((word (make-vector word-size 0))) ; a new mutable vector
      (loop
        for digit-index from (1- word-size) downto 0
        for current = integer then (truncate current base)
        for digit = (mod current base)
         do (setf (aref word  digit-index) digit))
      word))

(integer-to-base 42 2 8)  ; --> [0 0 1 0 1 0 1 0]
(integer-to-base 42 8 8)  ; --> [0 0 0 0 0 0 5 2]
(integer-to-base 42 24 4) ; --> [0 0 1 18]

-- 
__Pascal Bourguignon__
http://www.informatimago.com/