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.
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.
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.
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