From: Chad Perrin <code@...>
Date: 2012-01-30T14:56:52+09:00
Subject: Re: Microrant on Ruy's Math Skills

On Mon, Jan 30, 2012 at 10:03:04AM +0900, Gary Wright wrote:
> 
> On Jan 29, 2012, at 2:26 AM, Jon Lambert wrote:
> 
> > On Jan 27, 2012, at 3:26 PM, Gary Wright wrote:
> >> What 'value' do you expect for this expression:
> >> 
> >> BigDecimal("1.0") / BigDecimal("3.0")
> > 
> > Decimal math operations need use a default rounding context or require one to set a
> > rounding context before performing an operation.
> > 
> > Do you round towards +infinity, -infinity,
> > towards 0, away from 0,
> > to nearest (and if equidistant, round down),
> > to nearest (and if equidistant, round up), or
> > to nearest (and if equidistant, round so that the last digit is even) aka. bankers rounding?
> > 
> > Only then can you know what to expect.
> 
> Agree 100%.  I was just trying to illustrate that even if you have some
> wonderfully crafted big decimal literal syntax, you still need to address
> the context issues you just listed.
> 
> 	1.0D / 3.0D
> 
> Might be easier to type but it is only part (perhaps a small part) of the puzzle.

The point of offering something other than "all you get is floats and
libraries", of course, is that a simple set of such rules is a lot easier
to deal with than the floating point mess that is common now.  It's a lot
easier to deal with "it truncates decimals past the Nth place" or any
other such simple rule than "Uh . . . it's probably going to do some
weird shit when you start doing math -- weird shit that requires you to
do binary math to predict the outcome.  You really just shouldn't use
it.  Use some verbose library syntax instead.  You like typing -- right?"

-- 
Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]