Why are the Math functions so insanely slow?

programming flash
1 

import flash.utils.getTimer;
var n:Number = 1.5;
var st:Number = getTimer();
var test:int;

function divT():void {    
    st = getTimer();
    for(var i:int=0;i<10000000;i++) {
        test = Math.floor(n);
    }
    trace("Time spent calculating with Math.Floor: " +(getTimer()-st)+ " ms");
}

function divB():void {    
    st = getTimer();
    for(var i:int=0;i<10000000;i++) {
        test = int(1.5);
    }
    trace("Time spent calculating with conversion to int: " +(getTimer()-st)+ " ms");
}

divT();
divB();

Whereas I see and understand the results, I don’t get why the built in floor function is so incredibly slow compared to int conversion.

Can anyone shed some light on this?

2

For those that don’t feel like trying it, this is what it traces out for me;


Time spent calculating with Math.Floor: 721 ms
Time spent calculating with conversion to int: 34 ms
3

I believe this is the code (it’s not AS, obviously) used for [FONT=“Courier New”]Math.floor()[/FONT]:


#include "fdlibm.h"

#ifdef __STDC__
static const double really_big = 1.0e300;
#else
static double really_big = 1.0e300;
#endif

#ifdef __STDC__
	double fd_floor(double x)
#else
	double fd_floor(x)
	double x;
#endif
{
        fd_twoints u;
	int i0,i1,j0;
	unsigned i,j;
        u.d = x;
	i0 =  __HI(u);
	i1 =  __LO(u);
	j0 = ((i0>>20)&0x7ff)-0x3ff;
	if(j0<20) {
	    if(j0<0) { 	/* raise inexact if x != 0 */
		if(really_big+x>0.0) {/* return 0*sign(x) if |x|<1 */
		    if(i0>=0) {i0=i1=0;} 
		    else if(((i0&0x7fffffff)|i1)!=0)
			{ i0=0xbff00000;i1=0;}
		}
	    } else {
		i = (0x000fffff)>>j0;
		if(((i0&i)|i1)==0) return x; /* x is integral */
		if(really_big+x>0.0) {	/* raise inexact flag */
		    if(i0<0) i0 += (0x00100000)>>j0;
		    i0 &= (~i); i1=0;
		}
	    }
	} else if (j0>51) {
	    if(j0==0x400) return x+x;	/* inf or NaN */
	    else return x;		/* x is integral */
	} else {
	    i = ((unsigned)(0xffffffff))>>(j0-20);
	    if((i1&i)==0) return x;	/* x is integral */
	    if(really_big+x>0.0) { 		/* raise inexact flag */
		if(i0<0) {
		    if(j0==20) i0+=1; 
		    else {
			j = i1+(1<<(52-j0));
			if((int)j<i1) i0 +=1 ; 	/* got a carry */
			i1=j;
		    }
		}
		i1 &= (~i);
	    }
	}
        u.d = x;
	__HI(u) = i0;
	__LO(u) = i1;
        x = u.d;
	return x;
}

With that much manipulation and evaluation it’s no surprise that it takes a while. All the [FONT=“Courier New”]int() [/FONT]function does is return the number before the ‘.’ - that can’t be a very complex function. (Try [FONT=“Courier New”]trace(int(1.999));[/FONT] for example, it still returns ‘1’.)

4

Well… try trace(Math.floor(1.9999));

:wink:

5 

trace(int(-1.5)); //traces -1
trace(Math.floor(-1.5)); //traces -2

:slight_smile: