Re: Undefined Behavior Optimizations in Fortran

On Thursday, January 26, 2023 at 11:00:02 AM UTC-8, gah4 wrote:


(snip)


> Now, the original subject of this thread, is the cost vs. benefit of such
> optimizations. Not so obvious the benefit, but there is a cost when people
> try to debug programs where things are optimized away.


> [Gee, it's been a while since I thought about SSP. I believe that IBM wrote
> it largely to give people code that would get reasonable numeric answers
> with the 360's funky floating point. Then there were a few odds and ends
> like RANDU. They never promised the code would work on anything other
> than IBM 360 Fortran. -John]


It seems that there is also SSP for the IBM 1130, which is 16 bit binary,
so probably also a 32 bit two's complement integer.


There is a PL/I SSP, but seems not to have RANDU.


When I was in high school, we had CALL/OS, with PL/I, and
I used the RANDU algorithm, as I didn't have any other one.


As you say, it wasn't promised to work with any other Fortran,
but others did try to stay compatible with IBM.
(But often with non-IBM extensions.)


Fortran systems that I know, are good at ignoring fixed point
overflow, though often trap or count floating point overflow.
[I took a look, RANDU on the 1130 repeated after 2^13 items.
Yow. -John]

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