On 8/28/2022 12:26 AM, gah4 wrote:
> On Saturday, August 27, 2022 at 3:13:09 PM UTC-7, Thomas Koenig wrote:
>> gah4 <ga...@u.washington.edu> schrieb:
>>> On Saturday, August 27, 2022 at 2:30:15 AM UTC-7, Thomas Koenig wrote:
> (snip)
>>>> Really? You mean that
>
>>>> DO 10 I=0,1
>
>>>> would not be allowed?
>
>>> Yes, not allowed.
>
>> I have the Fortran 66 standard before me, and I find no such
>> restriction in 7.1.2.8 (nor would it make sense at all).
>
>> Which part of the standard are you referring to?
>
> Yes 7.1.2.8.
>
> "At time of execution of the DO statement, m1, m2, and m3 must be greater than zero."

What ? Our code has negative indexes dating back to F66 days. I am
assuming that this is:

DO 10 I = ncp, 1, -1

Lynn

Lynn McGuire <lynnmcguire5@gmail.com> schrieb:
> On 8/28/2022 12:26 AM, gah4 wrote:
>> On Saturday, August 27, 2022 at 3:13:09 PM UTC-7, Thomas Koenig wrote:
>>> gah4 <ga...@u.washington.edu> schrieb:
>>>> On Saturday, August 27, 2022 at 2:30:15 AM UTC-7, Thomas Koenig wrote:
>> (snip)
>>>>> Really? You mean that
>>
>>>>> DO 10 I=0,1
>>
>>>>> would not be allowed?
>>
>>>> Yes, not allowed.
>>
>>> I have the Fortran 66 standard before me, and I find no such
>>> restriction in 7.1.2.8 (nor would it make sense at all).
>>
>>> Which part of the standard are you referring to?
>>
>> Yes 7.1.2.8.
>>
>> "At time of execution of the DO statement, m1, m2, and m3 must be greater than zero."
>
> What ? Our code has negative indexes dating back to F66 days. I am
> assuming that this is:
>
> DO 10 I = ncp, 1, -1

Hm. Seems like this was carried over from the very first FORTRAN.
The 1956 Programmer's Reference Manual restricted them to unsigned
fixed point constants.

Looking at the Fortran IV language at
http://www.bitsavers.org/pdf/ibm/360/fortran/C28-6515-6_FORTRAN_IV_Language_1966.pdf
we have the same restriction.

So, seems like an extension at the time (a very useful one, too).

On Sunday, August 28, 2022 at 11:42:28 AM UTC-7, Lynn McGuire wrote:
> On 8/28/2022 12:26 AM, gah4 wrote:

(snip, I wrote)

> > "At time of execution of the DO statement, m1, m2, and m3 must be greater than zero."

> What ? Our code has negative indexes dating back to F66 days. I am
> assuming that this is:
> DO 10 I = ncp, 1, -1
Many systems had extensions to Fortran 66, and that might not have been unusual.

Those competing with IBM needed a way to make there systems look better,
and such extensions were one way to do it. DEC had a lot of extensions like that.

On the other hand, IBM was careful with theirs. The had some big extensions
where there was no way around them. END= on READ was very useful!

But DO look changes that were easy to make with a temporary variable
did not get an extension. Making m3 negative means that the test
has to be inverted. IBM Fortran IV compilers don't change the test.

As note, though, IBM Fortran IV compilers will also disallow:

DO 10 I=0,9

though if you use a variable set to 0, it works just fine.
(Unless the optimizer figures it out, and disallows it.)

Similarly,

DO 10 I = ncp, 1, -1

won't compile. If you use a variable set to -1, it will
loop until the variable wraps to a large value.

On Sunday, August 28, 2022 at 1:17:22 PM UTC-7, Thomas Koenig wrote:

(snip)

> Hm. Seems like this was carried over from the very first FORTRAN.
> The 1956 Programmer's Reference Manual restricted them to unsigned
> fixed point constants.
> Looking at the Fortran IV language at
> http://www.bitsavers.org/pdf/ibm/360/fortran/C28-6515-6_FORTRAN_IV_Language_1966.pdf
> we have the same restriction.
> So, seems like an extension at the time (a very useful one, too).

It is not so hard to do with a constant, but IBM didn't do that. It is harder
with a variable, as the test direction depends on the sign.

IBM S/360 compilers use BXLE, Branch on indeX Less than or Equal, to
increment and test, at the end of the loop.

IBM was always good at marking their extensions with gray shading in the
manuals.

On Monday, August 29, 2022 at 4:42:28 AM UTC+10, Lynn McGuire wrote:
> On 8/28/2022 12:26 AM, gah4 wrote:
> > On Saturday, August 27, 2022 at 3:13:09 PM UTC-7, Thomas Koenig wrote:
> >> gah4 <ga...@u.washington.edu> schrieb:
> >>> On Saturday, August 27, 2022 at 2:30:15 AM UTC-7, Thomas Koenig wrote:
> > (snip)
> >>>> Really? You mean that
> >
> >>>> DO 10 I=0,1
> >
> >>>> would not be allowed?
> >
> >>> Yes, not allowed.
> >
> >> I have the Fortran 66 standard before me, and I find no such
> >> restriction in 7.1.2.8 (nor would it make sense at all).
> >
> >> Which part of the standard are you referring to?
> >
> > Yes 7.1.2.8.
> >
> > "At time of execution of the DO statement, m1, m2, and m3 must be greater than zero."
> What ? Our code has negative indexes dating back to F66 days. I am
> assuming that this is:
>
> DO 10 I = ncp, 1, -1
..
All of these were valid in PL/I from the beginning (1966) --
negative increments, initial values starting at zero or even negative.
..
As well, a PL/I loop could be executed 0 times (inlike FORTRAN
which, at that time, insisted in executing a loop at least once,
even if the initial value was greater than the final value).

On Monday, August 29, 2022 at 7:05:08 AM UTC+10, gah4 wrote:
> On Sunday, August 28, 2022 at 11:42:28 AM UTC-7, Lynn McGuire wrote:
> > On 8/28/2022 12:26 AM, gah4 wrote:
> (snip, I wrote)
> > > "At time of execution of the DO statement, m1, m2, and m3 must be greater than zero."
>
> > What ? Our code has negative indexes dating back to F66 days. I am
> > assuming that this is:
>
> > DO 10 I = ncp, 1, -1
> Many systems had extensions to Fortran 66, and that might not have been unusual.
>
> Those competing with IBM needed a way to make there systems look better,
> and such extensions were one way to do it. DEC had a lot of extensions like that.
>
> On the other hand, IBM was careful with theirs. The had some big extensions
> where there was no way around them. END= on READ was very useful!
>
> But DO look changes that were easy to make with a temporary variable
> did not get an extension. Making m3 negative means that the test
> has to be inverted. IBM Fortran IV compilers don't change the test.
>
> As note, though, IBM Fortran IV compilers will also disallow:
>
> DO 10 I=0,9
>
> though if you use a variable set to 0, it works just fine.
> (Unless the optimizer figures it out, and disallows it.)
>
> Similarly,
> DO 10 I = ncp, 1, -1
> won't compile. If you use a variable set to -1, it will
> loop until the variable wraps to a large value.
..
You might have to wait a long time for that to happen.