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comp.lang.lisp

Re: Converting numbers into sequences of bytes

William James

8/8/2015 5:16:00 AM

Bjorn Lindberg wrote:

> Here is a function to turn an integer into an array of high-to-low
> order bytes:
>
> (defun integer->bytes (n)
> (loop for i = n then quot
> for (quot rem) = (multiple-value-list (floor i 256))
> collect rem into result
> while (> quot 0)
> finally (return (make-array (length result)
> :element-type '(unsigned-byte 8)
> :initial-contents (nreverse result)))))
>
> (integer->bytes (expt 2 32))
> ==> #(1 0 0 0 0)
> (integer->bytes (1- (expt 2 32)))
> ==> #(255 255 255 255)

Gauche Scheme:

(use srfi-1 :only (unfold-right))

(define (integer->bytes n)
(list->vector
(unfold-right zero? (cut mod <> 256) (cut div <> 256) n)))


(integer->bytes (expt 2 32))
===>
#(1 0 0 0 0)

(integer->bytes (- (expt 2 32) 1))
===>
#(255 255 255 255)

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