[Info-vax] VMS Software Q1 '23 Update

[Johnny Billquist]

On 2023-01-29 15:51, Simon Clubley wrote:
> On 2023-01-29, Arne Vajhøj <arne at vajhoej.dk> wrote:
>> On 1/29/2023 1:21 AM, Dave Froble wrote:
>>> On 1/28/2023 10:44 PM, Arne Vajhøj wrote:
>>>> On 1/28/2023 10:39 PM, Dave Froble wrote:
>>>>> On 1/28/2023 8:28 PM, Scott Dorsey wrote:
>>>>>> One of the absolute FIRST things that I was told about floating point
>>>>>> variables in my first programming class was to NEVER use them to
>>>>>> represent
>>>>>> money.
>>>>>
>>>>> What if you didn't have a choice?
>>>>>
>>>>> RSTS/E V04b
>>>>>
>>>>> Signed word integers
>>>>> Strings
>>>>> Single and double D-float
>>>>>
>>>>> That's all there was ...
>>>>
>>>> There is always integers and implied decimal.
>>>>
>>>> Not fun though.
>>>>
>>>> And one need an integer with enough bits ...
>>>>
>>>> Could PDP-11 do 32 bit integers?
>>>
>>> What part of "signed word integers" didn't you understand?  As in 16
>>> bits. -32768 to 32767.
>>
>> I sort of had guessed that word was the same as on VAX,
>> but I don't understand how it can't have a 32 bit integer.
>>
>> How does one work with file sizes and file position
>> in bytes on PDP-11?
>>
> 
> The same way as it's done with a block-based filesystem (ODS-2) on VMS.

If you look at the QIO functions to F11ACP in RSX, the block number take 
two parameters, in order to be 32 bits. Fields in RMS structures are 
simply just 32 bits where needed, if you deal at it at that level.

> In general, the 16-bit nature of the PDP-11 is reflected in the API.

Not sure which API you are referring to here. The QIO interface 
obviously have just 16-bit wide arguments, so something like the block 
number needs to parameter values for the full 32 bits.
Most other APIs (such as FCS or RMS) just define 32-bit values where needed.

> Ever worked with real-mode MS-DOS at assembly language level ?
> 
> It's the same kind of thing.

No. Not at all comparable. The PDP-11 is rather different than the x86. 
There was never far pointers, segment registers, or all the weird stuff 
of MS-DOS.

>> I know you don't do C, but I believe C was invented on
>> PDP-11.
>>
> 
> What makes you think that "int" in C is _always_ at least 32 bits ? :-)
> 
> There's a reason why both int and long int have always existed in C.
> 
> And on architectures that do not support 32-bit ints, then long int is
> a library/RTL feature implemented by the language in the same way as
> 64-bit long long int is implemented by the language RTL on 32-bit
> architectures.

Um. Not necessarily. The compiler can just know how to do 32-bit 
operations on a 16-bit machine, and generate the code straight off, even 
if it's a bit more complex than simple 16-bit operations.

And that is what I see for PDP-11 C for example.

> Also, most languages on RSTS/E intended for commercial data processing
> also supported a decimal datatype, which was implemented by the language's
> RTL. It seems early RSTS/E Basic wasn't one of them however, based on
> what David is saying.

You could definitely argue that the numeric strings are a decimal data type.

   Johnny