6502.org

Posted: **Sun Sep 08, 2019 4:46 am**

So you actually were able to measure the difference ... cool! I have a slightly different use case for my current coding exercise. It's for my new version of MSBASIC's FIN, which I cheekily renamed atof:

Code: Select all

getnxt:
      iny               ; bump the buffer pointer
gettxt:
      lda   (txtptr),y  ; grab a char from text buffer
      cmp   #' '        ;
      beq   getnxt      ; skip over any space char(s)
      eor   #'0'        ;
      cmp   #10         ; ASCII decimal digit?
      bcc   gottxt      ;   yes: CC, convert to binary
      eor   #'0'        ;   no: CS, return orig. ASCII
gottxt:
      rts               ;

Here, I assume that we're still in the land of NMOS, that the current string of interest is smaller than 256 bytes, and that scanned decimal digits will be used as binary immediately.

Posted: **Sat Oct 19, 2019 3:12 pm**

I've started looking at what changes I can make to the Commodore 64's BASIC to take advantage of the new instructions in my 65020 design (which I'm working on again, slowly).

Profiling a simple test program showed that a huge amount of time is spent in CHRGET / CHRGOT. This routine always struct me as overcomplicated. Surely you don't always need to know if the character you've fetched is a digit - why go through that lengthy test every time, only to ignore the carry flag when you return?

If you have an LDA (zp) instruction without indexing, it's possible to replace many (but not all) calls to CHRGOT with an inlined LDA (TXTPTR). There's no need to test for space and loop, because CHRGOT can never be called on a space.

So I tried that on one instance, and ... well, it does work, and it does make difference. But in the process I've discovered a latent bug. The program would crash with a "NEXT WITHOUT FOR" error, unless I followed the LDA (TXTPTR) with a NOP.

Here's the code responsible:

Code: Select all

DOPRE1	LDA OPTAB+2,Y
	PHA
	LDA OPTAB+1,Y
	PHA
	JSR PUSHF1
	LDA OPMASK
	JMP LPOPER
SNERR5	JMP SNERR
PUSHF1	LDA FACSGN
	LDX OPTAB,Y
PUSHF	TAY
	PLA
	STA INDEX1
	INC INDEX1
	PLA
	STA INDEX1+1
	TYA
	PHA

The JSR PUSHF1 pushes the address of (one byte before) the next instruction. PUSHF then pops this address, increments it, and stores it in INDEX1. Later on there's a JMP (INDEX1). Can you see the problem?

It's only incrementing the low byte of INDEX1. My changes placed the instruction after JSR PUSHF1 at the start of a page, so the address pushed to the stack ended in $ff. Increment just the low byte of that, and JMP (INDEX1) will take you 256 bytes from where you should be.

It's not a problem in the Commodore 64, because that instruction is normally nowhere near the start of a page. I just got very, very unlucky.

Posted: **Thu Oct 24, 2019 3:23 pm**

Quote:

Funny thing..., the only Microsoft software to ever run on Apple computers were MS Basic and MS Office.. Or am I wrong?

They also published Olympic Decathalon for the Apple ][...

Posted: **Thu Oct 24, 2019 7:28 pm**

TomC wrote:

Quote:

Funny thing..., the only Microsoft software to ever run on Apple computers were MS Basic and MS Office.. Or am I wrong?

They also published Olympic Decathalon for the Apple ][...

And also Multiplan, a pretty good spreadsheet program.

Posted: **Fri Oct 25, 2019 5:42 pm**

Let's not forget their CP/M card for the Apple II. That was a big seller for them for a while.
I'm sure it had custom ROM code at the very least.

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Microsoft Basic listing from 1978

Re: Microsoft Basic listing from 1978

Re: Microsoft Basic listing from 1978

Re: Microsoft Basic listing from 1978

Re: Microsoft Basic listing from 1978

Re: Microsoft Basic listing from 1978