> On Wed, Sep 17, 2008 at 10:53 PM, Maciej Stachowiak <[EMAIL PROTECTED]> wrote: > I think it is a tenable position that 1.5m === 1.5000m based on the > "cohort" concept, since performing the same operation on both will > give answers that are in the same "cohort" equivalence class. But 1. > 5 / 10.0 != 1.5m / 10.0, and indeed, the answers would not even be > in the same cohort. A notion of 'cohort' equivalence class based on > correspondence in the abstract to the same real number but divorced > from the actual semantics of the programming language strikes me as > incoherent. I think such a notion of equivalence class only makes > sense if performing identical operations on members of the same > cohort gives answers which are in the same cohort. > > Are -0 and 0 in the same cohort?
In IEEE 754, no: 2.1.10 cohort: The set of all floating-point representations that represent a given floating-point number in a given floating-point format. In this context ?0 and +0 are considered distinct and are in different cohorts. (+0 and -0 are distinguishable in binary FP as well as in decimal FP; in fact this is the only case in binary where two finite numbers have the same value but different representations and encodings.) Mike Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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