I am working on a rotation function that updates player's pitch and yaw based on the location of a block or entity near the player. I understand how to compute the angular change, theta, required from the players current look vector to the desired look vector using 2d or 3d vectors yada yada yada...

 

All that being said when I am reviewing rotation functions that others have coded I see something like:

                final double d0 = x - mc.thePlayer.posX;
	final double d1 = z - mc.thePlayer.posZ;
	final double d2 = y - mc.thePlayer.posY - mc.thePlayer.getEyeHeight();
	final double d3 = d0 * d0 + d2 * d2 + d1 * d1;

	if (d3 < 2.500000277905201E-7D) {
		return 0;
	}
                //DoStuff

 

So my question is what is the significance of the number 2.500000277905201E-7? I haven't been able to find useful posts about it.

 

 

First of all, that number is really just 2.5^-10 (or 0.00000025). The small part at the end is a rounding error, watch

for some background.

 

What this code does is just clamp some value that probably gets progressively smaller to 0 at some very small value. This is to remove weird things caused by smaller and smaller values that are still not 0.

 

I understood the number itself and how floating point conversions are lossy (btw 2.5x10^-7 == 0.00000025 != 2.5^-10). I was only curious why it was being used there. It makes sense to clamp off the number at some small value though.

 

Thanks! I appreciate your explanation!

First of all, that number is really just 2.5^-10 (or 0.00000025)

 

These are not the same thing.

2.5^-10 is 0.0001048576

I think you meant 2.5 * 10^-10

 

Also, you probably meant -7, not -10.

First of all, that number is really just 2.5^-10 (or 0.00000025)

 

These are not the same thing.

2.5^-10 is 0.0001048576

I think you meant 2.5 * 10^-10

 

Also, you probably meant -7, not -10.

yup. I caught that too. easy mistake to make sometimes.

I was tired, ok?

 

I'm mostly teasing. I made that post right after having a conversation involving Knuth's Up-Arrow Notation and an idle/clicker game.

(And the number 5.6↑↑3)

Oh god, not

...

 

5.6↑↑3 is only about 1 * 10²⁴

(It's less now that I plug it into a calculator, but I was working backwards and just wanted something close; 5.65 is better)

I know it's not that big. I just remember those weird arrows from that video

 

Yup!  Two arrows and a small number on the end is rather reasonable. It's when you get 4+ that things go stupid.

 

(Windows calculator gives up at 5.65↑↑7)

I know it's not that big. I just remember those weird arrows from that video

 

Yup!  Two arrows and a small number on the end is rather reasonable. It's when you get 4+ that things go stupid.

 

(Windows calculator gives up at 5.65↑↑7)

What do these arrows even mean and how to write them on a PC?