EX is a very funny instruction in the 360 series and works as follows:

 	LA	4,9		loads R4 with the constant 9
 	EX	4,COPY		executes the instruction COPY
*				OR'ing its 2nd byte with the
*				current content of R4
 	BR	14		return
COPY	MVC	TO(1),FROM	move chars from FROM to TO,
*				predefined length is zero which is
*				actually modified by EX

So one could write a self-modifying program without actually changing
the code.

Imre


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On Thu, 4 Nov 2004, Byron A Jeff wrote:

> On Wed, Nov 03, 2004 at 10:10:39AM +0100, dr. Imre Bartfai wrote:
>>
>>> On Mon, Oct 25, 2004 at 11:32:21AM -0400, Peter Johansson wrote:
>>>> Herbert Graf writes:
>
> Actually for the record, I wrote that piece of code. It's written in NPCI.
> I have a language spec here:
>
> http://www.finitesite.com/d3jsys/README-NPCI.html
>
>>>
>>> proc clearbits(copy char count, copy char start)
>>>  while (count)
>>>     portb:start = 0 // Clear the bit in PORTB referenced by start.
>>>     start = start+1
>>>     count = count-1
>>>  endwhile
>>> endproc
>>>
>>> The portb:start=0 line is a significant chunk of code because it represents
>>> a variable bit number. But the compiler gives a compact abstraction for the
>>> concept.
>>
>> Therefore I miss the EX assembly statement used in the IBM/360 (and
>> successors) architecture. Does know somebody similar on another
>> processors?
>
> I couldn't get a description from Google. What does that instruction do?
>
> BAJ
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