Re: [OT] GNU bc base conversion

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]



On Mon, Aug 31, 2015 at 1:06 PM, Warren Young <wyml@xxxxxxxxxxx> wrote:

> On Aug 31, 2015, at 10:05 AM, Mike - st257 <silvertip257@xxxxxxxxx> wrote:
> >
> > On Mon, Aug 31, 2015 at 11:15 AM, Warren Young <wyml@xxxxxxxxxxx> wrote:
> >
> >> ibase=A and obase=A
> >
> > Not sure how this helps me with my most recent example of bin_to_hex
> where
> > the ibase within the define clause wasn't honored.
>
> That’s because your bin_to_hex function is erroneously assuming that its
> input is just a string of digits that has no base interpretation, so that
> it can set ibase *after* bc has already seen the value, and that this will
> change the meaning of the prior input.
>

Explains the behavior.


>
> That’s just plain wrong: the prior input has already been interpreted.
> You can’t wind back the clock like that.  That sort of thinking only works
> in a string-based language like shell or Tcl, where a numeric string
> doesn’t take a meaning until you assign one.
>
> The correct form is:
>
>     ibase=A   /* needed only if ibase might not be 10 at this point */
>     obase=A   /* ditto */
>     obase=16  /* means 16-base-10 here */
>     ibase=2   /* no possibility of confusion */
>     10101011
>
> Result: AB, as expected.
>

Thank you.
We're in agreement, your solution _does_ work when piped or interactively.
Any order does not work from a definition stanza since base10 is
(apparently) not capable of being overrode with definitions.

tmp]$ grep bin_to_hex ~/.bcrc
#define bin_to_hex(b) { obase=16; ibase=2; return b; }
define bin_to_hex(b) { ibase=A; obase=A; obase=16; ibase=2; return b; }

tmp]$ echo "bin_to_hex(10101011)" | bc
9A2113
tmp]$ echo "ibase=A; obase=A; obase=16; ibase=2; 10101011" | bc
AB
tmp]$ echo "obase=16; ibase=2; 10101011" | bc
AB


>
> The tricky bit is that you can’t swap the second pair of ibase and obase
> settings, since that would cause bc(1) to interpret obase=16 in base 2:
> bc(1) will clamp “16” to 11, which in base 2 is 3-base-10.


Agreed.
Thank you, Warren.


I don't believe bc is the tool for this job since define stanzas don't
replicate the behavior as seen when used via piping or interactively. :-/

-- 
---~~.~~---
Mike
//  SilverTip257  //
_______________________________________________
CentOS mailing list
CentOS@xxxxxxxxxx
https://lists.centos.org/mailman/listinfo/centos




[Index of Archives]     [CentOS]     [CentOS Announce]     [CentOS Development]     [CentOS ARM Devel]     [CentOS Docs]     [CentOS Virtualization]     [Carrier Grade Linux]     [Linux Media]     [Asterisk]     [DCCP]     [Netdev]     [Xorg]     [Linux USB]
  Powered by Linux