Re: g++ 3.4.2 strange behavior

[John Max Skaller]

On Mon, 01 Nov 2004 20:42:13 +0100, Paul Schneider wrote:

This:

(1000.0 - 0.00) / 0.01

is an 'arithmetic constant expression' whereas this:

(b-a)/c

is not (see ISO C++ 5.19/3). So I think what is happening
is that the first case is evaluated at compile time,
and the second at run time. It seems that the
evaluations produce different results.

Try this option:

       -ffloat-store
           Do not store floating point variables in registers, and inhibit
           other options that might change whether a floating point value is
           taken from a register or memory.
                                                                                
           This option prevents undesirable excess precision on machines such
           as the 68000 where the floating registers (of the 68881) keep more
           precision than a "double" is supposed to have.  Similarly for the
           x86 architecture.  For most programs, the excess precision does
           only good, but a few programs rely on the precise definition of
           IEEE floating point.  Use -ffloat-store for such programs, after
           modifying them to store all pertinent intermediate computations
           into variables.