Re: C arithmetic, was Software proofs, was Are there different

On Wednesday, February 8, 2023 at 8:48:23 AM UTC-8, gah4 wrote:


(snip)


> Well, I have been wondering for years when we get a C compiler
> for the 7090 so we can test out sign-magnitude integers.


> I think the 7090 does 16 bit integers, at least that is what
> its Fortran compilers did, stored in 36 bit words.


  (snip)


> [The 704x/709x series did 36 bit sign-magnitude arithmetic. Fortran
> integers were limited to 15 bits plus a sign, probably because that
> was the size of addresses, and they expected integer arithmetic to
> be used only for counting and subscripts. In 709 Fortran II they
> expanded them to 17 bits, in 7090 Fortran IV they were finally a
> full word. -John]


OK, so 7090 C can use all 36 bits. When we get one.


I just remembered that the S/360 emulation to develop
OS/360 was done on the 7090. 36 bits would help!


It was the 15 bit integers on the 704 that gave us five digit
statement numbers in Fortran, originally 1 to 32767, and
(not much) later extended to 99999.


And over 60 years later, we still have 99999.


But also, the 704 Fortran, and I believe still the 7090,
indexes arrays from the end of memory toward the beginning.
[It did because for reasons I have never been able to figure out,
the 70x series subtracted rather than added the contents of
an index register to get the effective address. -John]

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