Assembly Averaging

scotta

I have 5 numbers in 5 RES variables.

A1
A2
A3
A4
A5

How do I toss the high and low values, then average ?

Mike Green

Define new RES variables "MaxVal", "MinVal", and "Total" and do:

   mov  MaxVal,A1   ' This can be made into a loop with
   mov  MinVal,A1   ' any number of variables, but this
   mov  Total,A1   ' is simpler when only a few variables
   add   Total,A2   ' are used
   min   MaxVal,A2
   max  MinVal,A2
   add   Total,A3
   min   MaxVal,A3
   max   MinVal,A3
   add   Total,A4
   min   MaxVal,A4   ' Note that this wouldn't necessarily
   max  MinVal,A4   ' be what you want if two or more
   add   Total,A5   ' values were the high or low values
   min   MaxVal,A5
   max  MinVal,A5
   sub   Total,MaxVal   ' Toss the high and low values
   sub   Total,MinVal   ' and divide by 3 to get average
   mov  MaxVal,#3   ' Reuse MaxVal and MinVal since
   shl   MaxVal,#14   ' they're not needed further
   mov   MinVal,#16
:divide cmpsub Total,MaxVal    wc
   rcl   Total,#1   ' See document called Propeller Guts
   djnz   MinVal,#:divide   ' Result is left in "Total"

Post Edited (Mike Green) : 3/5/2007 6:49:02 PM GMT

scotta

Your brain sees problems differently than mine does. It takes me 10 minutes to read
something like this before it clicks.

Sorry I didn't get back to you on this sooner.

Thanks,

Scott

Mike Green

There are a couple of things going on there
1) Accumulating a total of the points
2) Determining the maximum of the points
3) Determining the minimum of the points
4) At the end: Divide the total by the # of points
So:
1) At the beginning, we initialize MaxVal, MinVal, and Total to the 1st value
2) For each subsequent point (A2 - A5), we add it into the Total, use the max
instruction to determine the minimum value (I know it seems backwards,
but there it is ... It does work this way ... Look carefully at the instruction
description) and the min instruction to determine the maximum value.
3) There's a simple division by a constant (the number of points). Note that
I messed up with the constant value. It should be 5, not 3.
Mike

Lord Steve

Mike Green said...
I messed up with the constant value. It should be 5, not 3.

Did I miss something?· If you have 5 values and you toss the minimum and maximum values...you have 3 left over.· So, the average of 3 values is the sum divided by...3, not 5.

Mike Green

Lord Steve,
Thanks. You're absolutely correct. I forgot about the "tossing the max and min values". Oh well, I guess I'm more confused than usual today.
Mike