Negative numbers

[sayzer]

"...Keep in mind that all of the math and comparisons in PBP are unsigned."

Will you use that negative number in a math operation or is it just for a representation on LCD or sending via a serial comm. etc?

[Darrel Taylor]

Unless it has something to do with a previous version of PBP, can't say.
But this simple program comes up with 248 (-8). PBP 2.46

 @  __CONFIG    _CONFIG1H, _OSCS_OFF_1H & _HS_OSC_1H
define OSC 20
clear

remaining var byte
rows      var byte

rows = 8
remaining = -rows

stop

Something you might try is ...

remaining = 0 - rows

[RUBiksCUbe]

I'm not using it for any math operations, just to control the start of a for loop.

for i = remaining toremaining + (rows - 1)
    if i < 0 then
        messageScroll[writePos] = $0
    endif
    if i >= 0 and i < messagelength then
        messageScroll[writePos] = message[i]
    endif
    if i >= messageLength then
        messageScroll[writepos] = $0
    endif
    writePos = writePos + 1
next i

for some reason when remaining is negative this part "crashes"

[sayzer]

Hi RUBiksCUbe,

Where do you get this "Remaining" variable into negative? Are you setting it to "negative" somewhere before this loop as you stated in the example above?


Also, here I made the same code of yours in a different look.
It seems you only need the negative value for " messageScroll[writePos] = $0 "

for i = remaining to remaining + (rows - 1)

    if i < 0 then 
        messageScroll[writePos] = $0

    else

        if i < messagelength then 
           messageScroll[writePos] = message[i]
        else
           messageScroll[writepos] = $0
        endif

    endif

    writePos = writePos + 1


next i

Also, are you setting other variables to an initial value at the beginning?






--------------------------

[RUBiksCUbe]

At the very beginning I have

rows = 8
remaining = (0 - rows)

[Darrel Taylor]

Couple problems here.

As Sayzer pointed out ... "...Keep in mind that all of the math and comparisons in PBP are unsigned."

This means that

if i < 0 then

will always evaluate to FALSE. And the FOR loop will always terminate before executing anything because -8 is really 248 in PBP math (assuming byte vars).

You'll need to find positive numbers to work with.

[mister_e]

Or testing the MSB of the variable. If 1=> negative if 0=>positive.