[Python-Dev] Floating-point implementations

Mark Dickinson dickinsm at gmail.com
Wed Dec 10 11:42:10 CET 2008


On Tue, Dec 9, 2008 at 5:24 PM, Mark Dickinson <dickinsm at gmail.com> wrote:
> I don't know of any.  There are certainly places in the codebase that
> assume 56 bits are enough.  (I seem to recall it's something like
> 56 bits for IBM, 53 bits for IEEE 754, 48 for Cray, and 52 or 56 for VAX.)

Quick correction, after actually bothering to look things up rather
than relying on my poor memory:  VAX doubles have either *53*
(not 52) or 56 bit mantissas.  More precisely, the VAX G_floating
format has a 53-bit mantissa (52 bits stored directly, one implicit
'hidden' bit), while the (now rare) D_floating format has a 56-bit
mantissa (again, including the implicit 'hidden' bit).

Mark


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