[rrd-users] Re: RPN Tutorial with logical operators (AND/OR)?

Laurent LEVIER llevier at argosnet.com
Sun May 2 18:09:27 MEST 2004

At 17:25 02/05/2004, Hugo van der Kooij wrote:
>On Sun, 2 May 2004, Laurent LEVIER wrote:
>All of them are maths. The first * does work as the AND operator but the
>+ does not at all. I am not a RPN expert however.
Ok, so '*' means AND. That's what I was suspecting.

>You need to play the stack game and rewrite it part by part to a more
>common notation to figure this one out.
>         Compare L2:
>C2 = (in < $L2) ,in,$L1,GE,*,in,$L1,-,0,IF,in,$L2,GT,$L1,0,IF,+
>         Compare L1:
>C2 = (in < $L2) (in >= $L1) ,*,in,$L1,-,0,IF,in,$L2,GT,$L1,0,IF,+
>         Multiply these results (which equals to AND):
>C2 = ((in < $L2) * (in >= $L1)) ,in,$L1,-,0,IF,in,$L2,GT,$L1,0,IF,+
>         Lower with L1:
>C2 = ((in < $L2) * (in >= $L1)) (in - $L1) ,0,IF,in,$L2,GT,$L1,0,IF,+
>         Now rewrite in more common format:
>IF ((in < $L2) * (in >= $L1))
>THEN C2a = (in - $L1)
>ELSE C2a = 0

Ok, that's what I was thinking. I am lucky until now!

>         So where did C2a come from? Well, I needed a place holder as we
>         haven't finished yet.
>C2b = in,$L2,GT,$L1,0,IF
>C2b = (in > $L2) ,$L1,0,IF
>         In more common format:
>IF (in > $L2)
>THEN C2b = $L1
>ELSE C2b = 0
>         And finaly:
>C2 = C2a + C2b

Ok, so this '+' is really used to add the results of the 2 IF. This was my 
best assumption to the logic of this line, but I was not sure.

>The problem here lies that it only works if you use even spaced color
>intervals. But if these intervals are not equaly divided you should not
>use $L1 but ($L2 - $L1). Which would in the end result in:
>BTW: I assume here that $Lx stands for the color seperation levels.
Yes, L1...L18 are values for color range from Green to Red.
For interested people, it is simply adding 0x20 on colors:
Starting at Green: #00FF00
Towards Yellow: #FFFF40
Until Red: #FF0000

Here is the full list, I attached an example of the result. Looks like 
Arizona with grass.
    "AREA:C1#00FF00" \
   "STACK:C2#20FF08" \
   "STACK:C3#40FF10" \
   "STACK:C4#60FF18" \
   "STACK:C5#80FF20" \
   "STACK:C6#A0FF28" \
   "STACK:C7#C0FF30" \
   "STACK:C8#E0FF38" \
   "STACK:C9#FFFF40" \
   "STACK:C10#FFE038" \
   "STACK:C11#FFC030" \
   "STACK:C12#FFA028" \
   "STACK:C13#FF8020" \
   "STACK:C14#FF6018" \
   "STACK:C15#FF4010" \
   "STACK:C16#FF2008" \
   "STACK:C17#FF0000" \
   "STACK:C18#FF0000" \

The principle is basically simple. If value > upper level of color, then 
AREA (or STACK from 2nd to... layer) return upper-lower value.
Else return entry value - lower
Finally, stack it on the previous drawn layer.
After a while for the last color, simply stack the entry point - lower 
layer value

Many thanks for that explanation.
I may finally be able to draw that graphic properly.


Laurent LEVIER
Systems & Networks Security Expert, CISSP CISM

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