[Proj] Re: Re: Proj4 Bug (rtodms)
Gerald I. Evenden
gerald.evenden at verizon.mail
Thu Nov 9 13:47:07 EST 2006
On Thursday 09 November 2006 1:40 am, Glynn Clements wrote:
> cp wrote:
> > The numbers have effectively right and exact representations in ten-bytes
> > format, but the compiler instead of making r/60 makes r * 1/60 so it
> > changes a little thing. I precise that this is done without any
> > optimization (force no optimization) and with option "don't correct FDIV
> > flaw" (for old processors) and "no quick floating points".
> In that case, the Borland compiler is entirely useless for any code
> which makes non-trivial use of floating-point arithmetic.
> Even if this particular issue can be worked around, you are likely to
> encounter similar issues time and time again.
> Any compiler written by someone who doesn't understand that x/y and
> x*(1/y) aren't equivalent simply isn't worth the disk space it
That argument does not hold too well. I altered the origin problem as
static int res1,res2;
// double tmp = 1./60.;
double tmp = 0.016666666666666666666666666666666666666;
// res1 = r / 60.;
res1 = r * tmp;
res2 = floor(r / 60.);
printf("%s\n",(res1==res2) ? "OK!" : "NOT OK!");
printf("res1: %d res2: %d\n", res1, res2);
Both cases (1/60., 0.01666--) run as:
res1: 4 res2: 4
using a temporary value for "1/60." a la Borland and in both cases the
procedure ran "OK."
I am still suspicious of the setting of the FPU's rounding flag.
This does raise in my mind: what should the default state of the rounding flag
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
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