Simulation - extension of byte to 32 bit.

[mnf]

A bug in the simulation engine.

The engine seems to use a 'longer than 8 bit' value in calculations and 8 bit values don't seem to be extended correctly..

sim_bug.fcfx

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Demonstrates this.

This may be by design - byte is described as 0..255 so my treating it as as signed 8 bit number might be wrong here?

Martin

[Benj]

Hi Martin,

Thanks that;s an interesting one. Does this work as expected on hardware?

[mnf]

I'll try it - I assumed it would since it would do an 8 bit comparison for a byte,,, But it might not?

Martin

[mnf]

No - doesn't work on hardware (indeed the code is optimised out to for the =-1 side of the conditonal)

I see it is defined as an unsigned char (MX_UINT8) - so I suppose this is the correct behaviour (as it should = 255 here)

Strangely if I define a variable x as (initial value) -1 then

Code: Select all

MX_UINT8 FCL_X = (0xffffffff);

is generated (some spare fs!)

I see there is a MX_SINT8 defined in the header files - but a signed byte variable isn't offered as a choice in the 'create a variable'

I think my 'cheating' and using -1 as a shorthand for 255 has led me astray here - the compiler is doing the correct thing....

Martin