Re: Infinite loop with GCC 4.3

[Han-Wen Nienhuys]

2008/5/26 Joe Neeman <address@hidden>:
> On Mon, 2008-05-26 at 10:09 +0200, Mats Bengtsson wrote:
>> As is taught in any course on numerical methods, you should always be
>> very careful with
>> comparing numerical values. For example you should use tests of the form
>> if (abs(x-y) < epsilon)
>> instead of
>> if (x==y)
>> where epsilon is a fixed value somewhat larger than machine precisions.

As others have pointed out, this is not really the problem here, but if you see

  if (abs(x-y) < eps)

you should be very suspicious; since eps is a constant, this code
depends on x and y always having roughly the same exponent. Eg.  this
will fail erroneously if x=0.999999999e10 and y=1.0e10.  For these
computations there is no real golden rule, except to use your brain,
and do an analysis of what is appropriate


-- 
Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen