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

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

Wed, 8 Feb 2023 01:10:49 -0800 (PST)

*From comp.compilers*

Related articles |

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) |

Re: C arithmetic, was Software proofs, was Are there different *DrDiettrich1@netscape.net (Hans-Peter Diettrich)* (2023-02-08) |

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) |

Re: C arithmetic, was Software proofs, was Are there different *DrDiettrich1@netscape.net (Hans-Peter Diettrich)* (2023-02-10) |

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

[3 later articles] |

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

**Newsgroups: ** | comp.compilers |

**Date: ** | Wed, 8 Feb 2023 01:10:49 -0800 (PST) |

**Organization: ** | Compilers Central |

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

**Injection-Info: ** | gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="11349"; mail-complaints-to="abuse@iecc.com" |

**Keywords: ** | arithmetic |

**Posted-Date: ** | 08 Feb 2023 11:48:20 EST |

**In-Reply-To: ** | 23-02-029 |

On Tuesday, February 7, 2023 at 6:30:40 PM UTC-8, Hans-Peter Diettrich wrote:

*> On 2/6/23 10:26 PM, gah4 wrote:*

*> > Too bad for those CDC computers, and Unisys computers.*

*> > Last I know of sign-magnitude is the IBM 7090 and 7094.*

*> AFAIK use IEEE-754 floating point numbers still sign-magnitude*

*> representation.*

*> Then the same representation of integral numbers may have advantages in*

*> computations.*

*> [I presume the sign-magnitude is to enable the hidden bit trick,*

*> which doesn't apply in unscaled integers. -John]*

Yes, I meant integer representation.

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.

As for floating point, the PDP-10 uses a two's complement

floating point format. It does two's complement on the

whole 36 bit word. The result is that fixed point compare

instructions work on floating point values.

[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]

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