Integer overflow

[Dutch]

Hi,

Im running in an issue where I found what happens, but cant solve it. I found here in flowcode forum and on line what possible to doo but changing the local variable in an U long does not solve it.

I took a part from my flowcode project and pasted it here. I have 4 8bit data numbers I receive and need to add those for a number to work with. the maximum number I have is inbeteween 0 and 400000 where in my program I need to do all kind of calculations with. turn out the maximum is 32767 for an signed/unsigned integer. how can I use bigger numbers? any tricks or changes I need to set?

the simulation don't show a fault mssage only the display shows a negative number. of coarse making a mess out of all my further calcualtions.
when I compile the message is 'integer overflow in expression'

(help... )

[mnf]

Hi Angelo,

One problem is that the LCD Print Number routine just takes a 16 bit integer (for the display you've used)

You could use ToStrings$ to convert a 32 bit integer to a string then print that...
Note that you use .data21 / 255 is this what you intended - or are the data elements just 4 bytes of a 32 bit number?
One way to avoid any problems (though not with the display)
Use n32 = d1 (extend d1 to 32 bit)
n32 = n32 << 8 + d2 (Left shift 8 bits and add on next 8 bits)
n32 = n32 << 8 + d3
n32 = n32 << 8 + d4
(Final no = d1d2d3d4 where d1..d4 are 8 bit nos and n32 is a 32 bit unsigned number)

Martin

[Dutch]

Hi Martin!

well I don't use the display to show that large number. but I use the number later in my calculations. the print on the display only was to show what goes wrong.

yes the calculation is correct. it are four separate received (Hexadecimal) 8bit numbers. (This is still in the program you helped me big time with last year!)

in the simulation in FC I can put in any number from 0 to 256 for all four bits and the result is fine. just in real the processor does wrong calculations above 32767.

Angelo

[mnf]

This gives the result as expected.....

Note that for left shift 8 bits you need * 256 (not 255) - I'd misread the screenshot on my phone before - you have 255 but are you sure this is what you need?

Integer overflow.fcfx

(8.39 KiB) Downloaded 213 times

Martin

[Dutch]

my bad 256 indeed. my bad. I changed the numbers to 256 in your code.

wow that looks it is what I need. I really need to sit down to see/understand what you did there.

[mnf]

Glad it's worked...

Let us know how the project goes...

Martin