Re: [vcf-midatlantic] Fwd: Floating point math in FORTRAN IV on PDP-8
On Sat, Sep 22, 2018 at 11:38 AM David Gesswein via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
On Sat, Sep 22, 2018 at 10:40:34AM -0500, Kyle Owen via vcf-midatlantic wrote:
I sent this over to cctalk and haven't found a taker to try out my FORTRAN code on another PDP-8 yet. Might any of you be able to try this out?
Should be able to next week if nobody else does first.
Thank you!
I tried running a simple program to print some natural logs and square roots, which ran quite well with the FPP8/A in place.
Without the FPP8/A...all of the results were wrong. Significantly. Negative numbers in many cases. No clear pattern as to what it's doing.
Are you are recompiling each time and not using a save file? The save file is only valid for the configuration it was built on.
Yes, recompiling each time.
Would anyone be able to try my program on some other real hardware (or another emulator) to verify? With and without EAE would also be desirable. I'm not sure how to disable the EAE in SIMH, else I'd try that too.
set cpu noeae
Ahh...excellent. Thanks! Kyle
Overflow resulting in negative numbers? How long is a float on a stock PDP-8? On Sat, Sep 22, 2018 at 12:48 PM Kyle Owen via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
On Sat, Sep 22, 2018 at 11:38 AM David Gesswein via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
On Sat, Sep 22, 2018 at 10:40:34AM -0500, Kyle Owen via vcf-midatlantic wrote:
I sent this over to cctalk and haven't found a taker to try out my FORTRAN code on another PDP-8 yet. Might any of you be able to try this out?
Should be able to next week if nobody else does first.
Thank you!
I tried running a simple program to print some natural logs and square roots, which ran quite well with the FPP8/A in place.
Without the FPP8/A...all of the results were wrong. Significantly. Negative numbers in many cases. No clear pattern as to what it's doing.
Are you are recompiling each time and not using a save file? The save
file
is only valid for the configuration it was built on.
Yes, recompiling each time.
Would anyone be able to try my program on some other real hardware (or another emulator) to verify? With and without EAE would also be desirable. I'm not sure how to disable the EAE in SIMH, else I'd try that too.
set cpu noeae
Ahh...excellent. Thanks!
Kyle
On Sat, Sep 22, 2018, 13:54 Dean Notarnicola <dnotarnicola@gmail.com> wrote:
Overflow resulting in negative numbers? How long is a float on a stock PDP-8?
The results seemed very random, so I'm not sure if it was overflow or something else. I need to get my system back together to test again. A float, as I recall, is stored in three 12-bit words with a 27 bit mantissa and a 9 bit exponent, each including their respective sign bits. Kyle
I did some testing with your program. Since it was without EAE you were having problems I used SIMH for testing so I didn't have to pull the cards out of my PDP-8. With the image you had problems with I see the same symptom. With http://www.pdp8online.com/pdp8cgi/os8_html?act=dir;fn=images/os8/hume.rk05;s... it seems to work ok. Note that one uses RKA0 and RKA1 for the two partitions. It also works if you copy this F4 distribution tape onto the image you were using. http://www.pdp8online.com/pdp8cgi/os8_html?act=dir;fn=images/misc_dectapes/D... Looks like the PDP-12 images I have don't work properly on a normal 8.
On Thu, Sep 27, 2018 at 1:47 PM David Gesswein via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
I did some testing with your program. Since it was without EAE you were having problems I used SIMH for testing so I didn't have to pull the cards out of my PDP-8. With the image you had problems with I see the same symptom. With
http://www.pdp8online.com/pdp8cgi/os8_html?act=dir;fn=images/os8/hume.rk05;s... it seems to work ok. Note that one uses RKA0 and RKA1 for the two partitions.
It also works if you copy this F4 distribution tape onto the image you were using.
http://www.pdp8online.com/pdp8cgi/os8_html?act=dir;fn=images/misc_dectapes/D...
Looks like the PDP-12 images I have don't work properly on a normal 8.
Very interesting; thanks for testing. Seems like there are certainly some bugs in certain FORTRAN versions. I'll stick with the working version you tested! Thanks again, Kyle
participants (3)
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David Gesswein -
Dean Notarnicola -
Kyle Owen