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

## gah4 <gah4@u.washington.edu>

Thu, 9 Feb 2023 00:26:11 -0800 (PST)

*From comp.compilers*

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Re: C arithmetic, was Software proofs, was Are there different *Keith.S.Thompson+u@gmail.com (Keith Thompson)* (2023-02-05) |

Re: C arithmetic, was Software proofs, was Are there different *gah4@u.washington.edu (gah4)* (2023-02-06) |

Re: C arithmetic, was Software proofs, was Are there different *DrDiettrich1@netscape.net (Hans-Peter Diettrich)* (2023-02-07) |

Re: C arithmetic, was Software proofs, was Are there different *gah4@u.washington.edu (gah4)* (2023-02-08) |

Re: C arithmetic, was Software proofs, was Are there different *anton@mips.complang.tuwien.ac.at* (2023-02-08) |

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**Re: C arithmetic, was Software proofs, was Are there different ***gah4@u.washington.edu (gah4)* (2023-02-09) |

Re: C arithmetic, was Software proofs, was Are there different *gah4@u.washington.edu (gah4)* (2023-02-09) |

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Re: C arithmetic, was Software proofs, was Are there different *gah4@u.washington.edu (gah4)* (2023-02-10) |

Re: C arithmetic, was Software proofs, was Are there different *gah4@u.washington.edu (gah4)* (2023-02-11) |

Re: C arithmetic, was Software proofs, was Are there different *anton@mips.complang.tuwien.ac.at* (2023-02-11) |

Re: C arithmetic, was Software proofs, was Are there different *drb@ihatespam.msu.edu* (2023-02-12) |

| List of all articles for this month |

**From: ** | gah4 <gah4@u.washington.edu> |

**Newsgroups: ** | comp.compilers |

**Date: ** | Thu, 9 Feb 2023 00:26:11 -0800 (PST) |

**Organization: ** | Compilers Central |

**References: ** | 23-01-092 23-02-003 23-02-019 23-02-025 23-02-026 23-02-029 23-02-032 |

**Injection-Info: ** | gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="43799"; mail-complaints-to="abuse@iecc.com" |

**Keywords: ** | C, history, comment |

**Posted-Date: ** | 10 Feb 2023 13:15:39 EST |

**In-Reply-To: ** | 23-02-032 |

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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