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 //
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