IEFBR14 (was Re: IND$FILE)

[ben]

On 11/19/2018 5:27 PM, Eric Smith via cctalk wrote:
> On Mon, Nov 19, 2018 at 2:24 PM Sean Conner via cctalk <
> cctalk at classiccmp.org> wrote:
> 
>> I've always been amused by IEFBR14 ever since I heard about it.  I first
>> came across it by this quote:
>>          Every program has at least one bug and can be shortened by at least
>>          one instruction---from which, by induction, one can deduce that
>>          every program can be reduced to one instruction which doesn't work.
>> IEFBR14 was this program---one instruction long, and it contained a bug:
>>          http://en.wikipedia.org/wiki/IEFBR14
>>
> 
> By induction you should be able to reduce a program to zero instructions.
> On CP/M, you actually can, and the resulting program is useful, and as far
> as I know, has zarro boogs. (Which instruction could a bug be in?)
> 
That expains why you never see computers with the single instruction
Subtract and branch on condition.