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Re: converting numbers to strings in arbitrary base (up to 36)
From: |
Mirko |
Subject: |
Re: converting numbers to strings in arbitrary base (up to 36) |
Date: |
Tue, 15 Mar 2011 13:57:48 -0700 (PDT) |
User-agent: |
G2/1.0 |
On Tuesday, March 15, 2011 3:15:23 PM UTC-4, Pascal J. Bourguignon wrote:
> Mirko <address@hidden> writes:
>
> > This is an elisp question:
> >
> > I can specify integers in base 2-36 using #xyr..., and I can read them from
> > a file.
> >
> > But is there a way to write an integer in arbitrary base (again, 2-36) to a
> > file?
> >
> > I looked at string-to-number, format, and calc
> >
> > In greater detail,
> >
> > I have a file where I want to keep a counter (in base 36).
> > When needed, I want to open the file, read the number.
> > Occasionally, I want to increment the number, and write it back out.
> >
> > I can handle reading and writing :-). It is writing the base 36 that
> > I don't know how to handle.
>
>
> For bases eight, ten, and sixteen, you can use format:
>
> (format "#8r%o #10r%d #16r%x" 42 42 42)
> --> "#8r52 #10r42 #16r2a"
>
>
>
> For the other bases, you must implement it yourself, or use
> integer-to-base (from
> http://git.informatimago.com/viewgit/index.php?a=viewblob&p=public/emacs&h=94650b080e8a38e9620687b9abd3fcb3e24c6561&hb=e57067965e5def38d5fa18dab0aa75cff3d049b9&f=pjb-utilities.el
> )
>
>
> (loop for b from 2 to 36
> collect (format "#%dr%s" b (integer-to-base 42 b)))
>
>
> --> ("#2r101010" "#3r1120" "#4r222" "#5r132" "#6r110" "#7r60" "#8r52"
> "#9r46" "#10r42" "#11r39" "#12r36" "#13r33" "#14r30" "#15r2C"
> "#16r2A" "#17r28" "#18r26" "#19r24" "#20r22" "#21r20" "#22r1K"
> "#23r1J" "#24r1I" "#25r1H" "#26r1G" "#27r1F" "#28r1E" "#29r1D"
> "#30r1C" "#31r1B" "#32r1A" "#33r19" "#34r18" "#35r17" "#36r16")
>
>
>
>
> (defun integer-to-base (decimal base &optional width padchar
> commachar comma-interval)
> "
> DO: Convert a decimal value into a string contening the
> same value expressed into the given base. 1<base<37.
> The optional WIDTH specifies the minimum length of the returned
> string (0-left-filled), not counting a '-' sign.
> SEE-ALSO:float-to-base."
> ;;TODO: Implement commachar, comma-interval
> (cond
> ((not (integerp base)) (error "Invalid base (%S)." base))
> ((or (< base 2) (< 36 base)) (error "Invalid base (%d)." base))
> ((not (integerp decimal))
> (error "For now, I only convert integer values.")))
> (let ((digits "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ")
> (buffer (make-string 32 ?0))
> (b 31)
> (sign "")
> )
> (if (< decimal 0)
> (setq sign "-"
> decimal (abs decimal)))
> (while (< 0 decimal)
> (let ((digit (% decimal base)))
> (aset buffer b (aref digits digit))
> (setq decimal (/ (- decimal digit) base)
> b (- b 1))))
> (if width (if (< 32 width)
> (setq sign (concat sign (make-string (- width 32) padchar))
> width 32)))
> (concat sign
> (if (and width (< (- 32 width) (+ 1 b) ))
> (substring buffer (- 32 width))
> (if (= b 31) "0" (substring buffer (+ 1 b)))))))
>
>
>
>
>
>
> --
> __Pascal Bourguignon__ http://www.informatimago.com/
> A bad day in () is better than a good day in {}.
Thanks to everyone
Mirko