FW: Interesting article on Slashdot! Undertanding the Technology

["Michael S Hines" <mshines () purdue edu>]

Interesting discussion on ASSEMBLER-LIST (IBM Assembler) - regarding how
knowing how a machine works (in Assembler Language) makes one a better
coder.

Interesting aside...   Noted below.  An attempt at optimization fails, due
to not providing the level of service expected of the instruction (setting a
return code or not).

Someone working at a high level of code (say COBOL) would never detect the
change - except to note perhaps that code that worked now fails...   Even if
that line of code wasn't touched.

I think it's called the Law of Unintended Consequences....

M.

-----------------------------------
Michael S Hines
[EMAIL PROTECTED]

-----Original Message-----
From: IBM Mainframe Assembler List [mailto:[EMAIL PROTECTED]
On Behalf Of Bob Rutledge
Sent: Friday, February 06, 2004 12:56 PM
To: [EMAIL PROTECTED]
Subject: Re: Interesting article on Slashdot!


Ray Mullins wrote:

...

> The blurb on the page has it exactly right - the best programmers are the
> ones that understand the architecture of the box they're dealing with.

And that on the day I got this:

<quote, slightly edited>
It was found that at the xxx yyy level, an "XR R15,R15"
instruction was replaced with an "SLR R15,R15" instruction
to improve instruction performance.  However, this rather
innocuous change had negative ramifications for other xxx
processes which relied on the instruction return code that is
set correctly with the XR instruction, but is not set
correctly with the SLR instruction.
</quote)

Yup.  Total grasp and understanding.  On both counts.

Bob