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

Hans-Peter Diettrich <DrDiettrich1@netscape.net>
Wed, 8 Feb 2023 15:24:55 +0100

          From comp.compilers
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From: Hans-Peter Diettrich <DrDiettrich1@netscape.net>
Newsgroups: comp.compilers
Date: Wed, 8 Feb 2023 15:24:55 +0100
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="12088"; mail-complaints-to="abuse@iecc.com"
Keywords: arithmetic
Posted-Date: 08 Feb 2023 11:50:16 EST
In-Reply-To: 23-02-029

On 2/7/23 2:31 PM, 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.
>
> DoDi
> [I presume the sign-magnitude is to enable the hidden bit trick,
> which doesn't apply in unscaled integers. -John]


That's correct, the inprecise representation of FP numbers allows for
such tricks. The hidden bit trick can be used again with the FP
exponents, as I outlined in my Dynamic Floating Point Exponents proposal
<https://figshare.com/articles/preprint/Dynamic_Exponents_for_Floating_Point_Numbers-2022-04-07_pdf/19548187>.


DoDi

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