Difference between X &lt; -20 and X < (-20) in Propeller Tool

dbpage

Why does the Propeller Tool give the following logical results?

X := -1
if X<-20 ...       ' TRUE
if X<(-20) ...     ' FALSE

ErNa

<- bitwise rotate left

dbpage

As the Propeller manual states, indention (one space or more) is critical!
Thanks

msrobots

@ErNa, what?

seems I missed that one. I know of '<=' biting me again and again, but '<-'?

And the first line seems to return the correct result, but the second not.

How is X defined?

curious.

Mike

Roy Eltham

In Spin, Logical FALSE is 0, and Logical TRUE is 0xFFFFFFFF (or -1 in a LONG).

Since -1 is 0xFFFFFFFF (assuming X is a LONG) and bitwise rotating (the <- operator) doesn't change it's value, it is still -1 (0xFFFFFFFF) which is TRUE.

Also, -1 is NOT less than -20, so your assumption that the second one is incorrect is wrong. The comparison operators do not change direction around zero. Numbers that are increasingly negative are less than numbers that or less negative.

Finally, you could have but a space between the < and the - in the first example, and it would have been the same as the one with parenthesis.

dbpage

ErNa,
Thank you for your succinct comment. It was a pleasant "ah ha" moment for me.

msrobots,
X is a long.

Roy Eltham,
Yes. X<-20 does not change its value and the result is TRUE.

My code comments should be read as describing the logical test result. The logical test -1 < -20 should be FALSE, as my comment, and you, point out.

As you point out, a space between < and - would have fixed the issue. X< -20 is the same as X<(-20).

Roy Eltham

dbpage,
My comment about the second one was directed at msrobots who said :"And the first line seems to return the correct result, but the second not." I should have been more clear.