[XOP] Set complete wave to NaN

 The following two functions can be used to set a complete wave with size entries to Nan. This is especially useful for images.
As I could not find anything in XOPSupport I created them myself. The *data pointers are returned from WaveData(waveHandle).
Tested on Windows XP 32bit.

<br />
void waveClearNaN64(double *data, long size){<br />
<br />
    long i;<br />
    for (i = 0; i < size; i++){<br />
        data[i] = DOUBLE_NAN;<br />
    }<br />
}<br />
<br />
void waveClearNaN32(float *data, long size){<br />
<br />
    long i;<br />
    for (i = 0; i < size; i++){<br />
        data[i] = SINGLE_NAN;<br />
    }<br />
}<br />
Dr. Jamie Boyd, Ph.D.
UBC In Vivo Imaging Core

If you already have a pointer to increment, why do you need i?

Incrementing two variables through a loop when one will do seems wasteful.

Maybe some c++ guru can tell us whether the compiler will optimize your code to be equivalent to the pointer arithmetic version.

September 17, 2010 at 12:48 pm - Permalink
@jamie:

Yes you have a point here. One alternative to write would be:
<br />
long i;<br />
for (i = 0; i < size; i++){<br />
    data[i] = DOUBLE_NAN;<br />
}<br />

or maybe even
<br />
void waveClearNaN64(double *data, long size){<br />
<br />
      double *lastEntry = &data[size-1];<br />
      while(data != lastEntry){<br />
        *data++ = DOUBLE_NAN;<br />
    }<br />
}<br />


I'll guess I will change it to the first version. From a speed POV I have not evaluated my solution properly I must admit.

September 20, 2010 at 12:16 pm - Permalink
I believe this:
void waveClearNaN64(double *data, long size){
 
      double *lastEntry = &data[size-1];
      while(data != lastEntry){
        *data++ = DOUBLE_NAN;
    }
}

has an off-by-one error. It does not set the last point. Change != to <=.

I think your original version was fine and probably as fast as the others. It was also straightforward and clear.

September 20, 2010 at 02:13 pm - Permalink

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