[GRASS5] r.contour crashes if step=0.5

[Markus Neteler]

Roger,

great!

On Sat, Jan 27, 2001 at 02:26:32PM +0100, Roger Bivand wrote:
> On Sat, 27 Jan 2001, Markus Neteler wrote:
> > On Sat, Jan 27, 2001 at 01:38:02PM +0100, Roger Bivand wrote:
> > > On Sat, 27 Jan 2001, Markus Neteler wrote:
> > > > On Sat, Jan 27, 2001 at 12:48:44PM +0100, Roger Bivand wrote:
> > > > > On Sat, 27 Jan 2001, Markus Neteler wrote:
> > > > > > 
> > > > > > r.contour crashes if step=0.5... Floating point exception.
> > > > > > I actually cannot see the problem. The offending line is a macro:
> > > > > > 
> > > > > >   dmax = (max->answer) ? atof (max->answer) : zmax - (int)zmax%(int)dstep;
> > > > > > 
> > > > > > dstep contains 0.5, zmax is determined my the program zmax=7.1231 here).
> > > > > 
[...]

> I think we need the fmod(x,y) function (K&R2: floating point remainder of
> x/y, same sign as x; y=0 needs to be trapped, p. 251 in my edition). So:
> 
> dmax = (max->answer) ? atof (max->answer) : zmax - (int)zmax%(int)dstep;
> 
> could be
> 
> dmax = (max->answer) ? atof (max->answer) : dstep == 0 ?
>         G_error(***) : zmax - fmod(zmax, dstep);
> 
> though I haven't tried it. 

I have rewritten the other macro accordingly:
Old:
dmin = (min->answer) ? atof (min->answer) : (int)zmin%(int)dstep?
                              zmin - (int)zmin%(int)dstep +dstep: zmin;

New:
dmin = (min->answer) ? atof (min->answer) : dstep == 0 ?
                   G_fatal_error("This step value is not allowed.") :
                   fmod(zmin,dstep) ? zmin - fmod(zmin,dstep) +dstep: zmin; 

And it seems to produce reasonable results:

Old macro with fp-exception if min/max not specified:
r.contour in=ph_upper out=ph_upper step=0.1 min=5.64 max=7.19
Reading data.
Percent complete:  100%
FPRange of data:    min =  5.647517 max = 7.195973
Minimum level will be 5.740000
Maximum level will be 7.190000
Continue?(y/n) [y]

New version:
New:
r.contour in=ph_upper out=ph_upper step=0.1
Reading data.
Percent complete:  100%
FPRange of data:    min =  5.647517 max = 7.195973
Minimum level will be 5.700000
Maximum level will be 7.100000
Continue?(y/n) [y] 

New:
r.contour in=ph_upper out=ph_upper step=0.1 min=5.64 max=7.19
Reading data.
Percent complete:  100%
FPRange of data:    min =  5.647517 max = 7.195973
Minimum level will be 5.740000
Maximum level will be 7.190000
Continue?(y/n) [y] 

r.contour in=ph_upper out=ph_upper step=0.1 min=5.647 max=7.196
Reading data.
Percent complete:  100%
FPRange of data:    min =  5.647517 max = 7.195973
Minimum level will be 5.747000
Maximum level will be 7.096000
Continue?(y/n) [y] 
Total levels:   15   Current level:        
Finished.

It's in CVS now.
Thanks Roger, many users like will me enjoy this fix.

 Markus

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