Re: COBOL myth busted, index versus subscript (MF on HP)

On Wed, 17 Oct 2007 12:24:09 -0700, Vivian <vsaegesser@xxxxxxxxxxx> wrote:

Very interesting test. For comparison purposes, I ran Robert's code
on our ancient mainframe (it's a very old slow box). Since I too was
curious about an array without an index defined, I created another
iteration of the test, to do the same 2 tests with an non-indexed
array. Here's my results:

NULL TEST 77
INDEX 93
SUBSCRIPT 150
SUBSCRIPT COMP-5 184
INDEX 1 52
SUBSCRIPT 1 118
SUBSCRIPT 1 COMP-5 154
NON-INDX 1 108
NON-INDEXED COMP-5 149

So it would appear on my box that an aligned index is fastest. But
interestingly, simply defining an index slows you down if you intend
to use a subscript. At least that's what happens on an MP3000.

So, Question, what is exit perform cycle? It gave me a compiler error
so I commented it out. Would that effect the results?

When I first ran the test, the null loop was empty. Micro Focus' optimizer was smart
enough to optimize it down to zero time. As a result, I had no measurement of loop
overhead to subtract. Exit perform cycle was added to make it go around the null loop
repeat-factor times. Since it was in the null loop's time, I had to add it to all the
other loops.

In your case, exit perform cycle was not necessary, so deleting it did not affect the
results.

I don't understand how defining an unused index could affect the speed of a subscripted
access. Can you compare generated code to see what the extra instruction does? What is
comp-5 and why is it slower?
.

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