On Tue, Dec 9, 2008 at 5:15 PM, Steve Holden steve@holdenweb.com wrote:
Is anyone aware of any implementations that use other than 64-bit floating-point? I'd be particularly interested in any that use greater precision than the usual 56-bit mantissa. Do modern 64-bit systems implement anything wider than the normal double?
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.)
Many systems have a "long double" type, which usually seems to be either 80-bit (with a 64-bit mantissa) or 128-bit. The latter is sometimes implemented as a pair of doubles, effectively giving a 106-bit mantissa, and sometimes as an IEEE extended precision type; I don't know how many bits the mantissa would have in that case, but surely not more than 117.
I asked a related question a while ago:
http://mail.python.org/pipermail/python-dev/2008-February/076680.html
Mark