Re: How to implement float min(float x, ...) ?
Re: How to implement float min(float x, ...) ?
- Subject: Re: How to implement float min(float x, ...) ?
- From: Kirk Kerekes <email@hidden>
- Date: Mon, 17 Nov 2008 12:21:49 -0600
How to implement float min(float x, ...) ?
I suggest you not use var_arg functions if you can avoid them.
So I propose a different path.
As a jumping-off point, here is a category method on NSData that
assumes that "self" (the NSData instance) is an array of floats:
(The -floats category method merely casts NSData's -bytes to return a
pointer-to-float, and the -floatlength category method divides -length
by sizeof(float).)
Note that this makes the NSData the memory equivalent of a C array/
vector, so you can now pass it to the Accelerate framework.
Any setup overhead is likely compensated for by the hardware accel of
vDSP (when available).
- (float) floatMinValueAndIndex:(int *) outIndex
{
float minValue = 0;
vDSP_minvi((void *)[self floats], 1, &minValue, outIndex, [self
floatLength]);
return minValue;
}
The following NSData class category method will convert an arbitrary
float array to the NSData required for the above:
+ (NSData *) floatsWithBlock: (float *) block count: (unsigned)
count // count of floats
{
NSData * result = [[self class] dataWithBytes: block length: (count *
sizeof(float))];
return result;
}
- (const float *) floats
{
return (const float *) [self bytes];
}
- (unsigned) count
{
return [self floatLength];
}
- (unsigned) floatLength
{
return [self length]/sizeof(float);
}
If performance is less of an issue than clarity, I would convert the
floats to an NSArray of NSNumbers, and then just sort the array using
the -sortedArrayUsing... methods. You get more information back -- not
just min, but max and next-to-min, and next-to-max, etc.
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