-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Chad Nelson Sent: Friday, April 02, 2010 8:10 PM To: boost@lists.boost.org Subject: Re: [boost] New Boost.XInt Library, request preliminary review
- ----------------8<---------------- Forgive any mathematical terminology errors, I'm only an armchair mathematician. But in the domain of natural numbers, zero, by definition, has no sign. It's neither positive nor negative (or if you prefer, it's both). Signed zero seems to be an invention of computer science, where it represents a fraction that's so small that the inexact computer representation is indistinguishable from zero, but where the number itself isn't necessarily true zero. - ----------------8<----------------
As such, there's no real need for it in XInt.
Is it possible to simply be agnostic to the sign bit when the mantissa is 0?
Isn't that the same as saying that -0 is identical to +0?
IMO this is computing - whatever mathematicians feel about it. 1 There *really is a sign bit*, so either we should ensure that it is never set with zero (which *might* involve some runtime cost - if we negate a value, so we have to check for zero?) or just accept acknowledge that it is there ? 2 Is it relevant that that floating point types have sign and copysign functions that might be applied by some generic code to this 'user-defined' type? Would be simplest for these to be provided and to do the obvious thing? Or are we saying that this can't be used in this way? 3 Likewise there *really is a limit to the size of this infinite sized integer*, and many users will want to place an arbitrary limit on its size (and to know that that is). "Calculate Fib numbers, but don't use more than 1 Mbyte for it". 4 Some users may also want to limit the size to some chosen fixed arbitrary maximum number that is much smaller in order to mimic some of the fixed big integers about (128 bit, 256 bit, 100 decimal digits like NTL ZZ type etc). Would it be logical to provide the std::numeric_limits<integer>::max() function for this? And what about the std::numeric_limits digits and digits10()? All these decisions seem to me arbitrary and pragmatic. Perhaps we should leave the author to make a full proposal with some use case and provide a rationale and pros and cons. Paul --- Paul A. Bristow Prizet Farmhouse Kendal, UK LA8 8AB +44 1539 561830, mobile +44 7714330204 pbristow@hetp.u-net.com