SINe function

[JPL]

on page 61 of Diablo16 Internal function Manual , section 2.3.5 SIN(angle) is example:

var myvar, angle;
angle := 133;
myvar := SIN(angle);
This example returns 92 in variable myvar.

OK, I assume, the variables myvar and angle are integers.
That's a problem because sin (133) is 0.7341 and that is not an integer.
Beside it, sin (133) is not 92 ....

My question: purpose of this function ?

[JPL]

The same is on next page of the manual for COSine:

var myvar, angle;
angle := 133;
myvar := COS(angle);
This example returns -86 in variable myvar.

Cos (133) is not -86 .... that's -0.682 and that is not integer ! If I try to use float variable, I get an error message.

Any idea?

[John Kevin]

Hi,

As stated on the Diablo16 Internal Functions:

"The returned value range is from 127 to -127 which is a more useful representation for graphics work. The real sine values vary from 1.0 to -1.0 so appropriate scaling must be done in user code as required."

Since the result will be easier to plot on the display. Can I ask how do you want to process the data?

Perhaps, you might want to use the flt_SIN(&result, &floatval). Please refer to Section 2.21 Floating Point Functions of the Manual.

Best Regards,
Kevin

[JPL]

Hi Kevin,
I wish you and your company successful year 2020.
Yes, in my project I use the float sine function.
Just, not only understand the Sine/Cos functions on pages 61/62 ...

angle := 133;
myvar := COS(angle);
This example returns -86 in variable myvar.

What is -86 in this example?
Why range -127 to +127? Why not range -180 to +180 ?

[John Kevin]

Hi,

Thank you for your greetings and your kind words.
The range of -127 to 127 comes from a signed byte representation (one's complement).
The -86 is the value mapped on the given range.

Best Regards,
Kevin

[JPL]

Kevin,
I understand range <-127, +127>. That is < -2E7, +2E7 >. But I don't understand how you get expression

-86 = cos (133 )

Please, can you write me in mathematical form the function

angle := 133;
myvar := COS(angle);
This example returns -86 in variable myvar.

Thanks

Jiri

[John Kevin]

Hi Jiri,

I think that there is some misunderstanding. The -86 is the return value of the given function ranging from 127 to -127. This is not the real value for the cosine function. The real value ranges from 1 to -1. If you desire the real cosine values, you need to map the return value so you can scale it accordingly.

I hope this helps.

Best Regards,
Kevin