Suzy and her division results

[pwwit1]

Hello,

 

I'm really starting to like programming the Lynx, what a great little platform!

Recently I started to play around with doing simple divides with suzi, and they mostly work. Except when I have a remainder :\

 

So here is my little program that I test by inspecting the accumulator it reads the result in a debugger.

It takes the decimal value 15 and divides it by 20.

 

DCBA return 0, as expected

ML, the remainder, returns 15 - which I find weird. I would expect the remainder would be .75 in 16bit fixed point (7FFF or something similar). Am I reading the remainder correctly? Code is below

 

; Divisor
	lda #20
	sta SUZI_MATHP 
	stz SUZI_MATHN 

	; LSB of numerator
	lda #15
	sta SUZI_MATHH
	stz SUZI_MATHG
	stz SUZI_MATHF
	stz SUZI_MATHE

	SYS_SUZY_MATH_WAIT

	; result
	lda SUZI_MATHD   ; 0
	lda SUZI_MATHC   ; 0
	lda SUZI_MATHB   ; 0
	lda SUZI_MATHA   ; 0

	; remainder
	lda SUZI_MATHM   ; Remainder is 15?!
	lda SUZI_MATHL	 ; 0

My question is is there any simple way to divide two numbers that give a fractional result (say 0.5) and use that to multiply another number? Something like 20 / 40 * 100 = 50.

It seems so cumbersome using remainders to do this, I must be missing something.

 

Any suggestions are welcome

 

[42bs]

The remainder of 15 is correct (15 modulo 20 = 15).

 

SUZY does integer only. So if you want fixed point, you need to shift the input value accordingly.

 

So divide (15*100) by 20 and you get 75 (which is .75).

 

See apfel_2a.asm in new_bll.

 

 

 

[42bs]

BTW: No need to clear the high byte despite SUZI_MATHE which starts SUZY.

[pwwit1]

Cheers thankyou! Interestingly if I don't clear the high byte, in the emulator the math results always return 0xff. Using Handy

[42bs]

4 hours ago, pwwit1 said:

nterestingly if I don't clear the high byte, in the emulator the math results always return 0xff. Using Handy

Well, no my version (else my 128/256 byte intros would not work). But what you pay attention for is that the emulator does not use the same number of cycles for multiplication/division.